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CURRENT AGRICULTURAL AND ENVIRONMENTAL SITUATION IN THE BARD WATER DISTRICT: A Report Submitted to California Regional Water Quality Control Board-

Colorado River Basin Region on behalf of the Bard Unit Coalition Group

Author Charles A. Sanchez

Professor of Soil, Water, and Environmental Sciences University of Arizona

Charles Sanchez received his B.S. in Plant Science and his M.S. in Soil Science from New Mexico State University in 1980 and 1982, respectively. He received his Ph.D. in Soil Chemistry from Iowa State University in 1986. From 1986 through 1991, he served as assistant and associate professor at the University of Florida’s Everglades Research and Education Center. His work in Florida was focused on the development of “Best Management Practices” for the reduction of non-point source pollution to the Everglades. In 1991, he joined the faculty at the University of Arizona’s Yuma Agricultural Center where he served as the center’s Director and as Professor of Soil, Water, and Environmental Sciences for 15 years. In 2011, he stepped down as the center’s administrator to devote full time to his research and extension programs. His research over the past 25 years has been focused on soil and water management and non-point source pollution issues in vegetable crop production systems in the low desert. He has also worked on fate, transport, and human exposure of environmental `contaminants.

Authorization

Bard Unit Coalition Group (BUCG) Mark Stover, President

The Bard Unit Coalition Group was established by landowners or agricultural waste dischargers within the BARD Unit to administer compliance issues with the California Water Resource Control Board- Colorado River Basin.

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Table of Contents

Executive Summary 2

1. Background

1.1 Irrigated Land in the Lower Colorado River Region 3

1.2 Bard Water District 4

1.3 Cropping Systems 5

1.4 Return Flows 6

2. On Farm Management

2.1 Irrigation Management 7

2.2 Salt Management 9

2.3 Fertilizer Management 10

2.4 Pesticide Management 12

3. Water Quality Monitoring

3.1 Fertilizer Nutrients 13

3.2 Other Inorganic Constituents 13

3.3 Pesticides 15

3.4 Emerging Contaminants 16

Literature Cited 16

i. List of Tables 21 ii. List of Figures 22

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EXECUTIVE SUMMARY

The Bard Water District (BWD) delivers Colorado River Water to 7,120 acres in the Bard Unit and 7,556 acres in the Reservation Unit. The canal and drainage systems for private and native trust lands are comingled. Agricultural production and practices in the BWD are similar to districts east of the river in Arizona and are focused on winter vegetable production. The private land within the BWD represents about 5% of the total agricultural production acres and about 10% of the return flows to the Colorado River in the Yuma area.

Irrigation efficiency in the BWD, like other districts in the Yuma area, are high and are the result of research and technology transfer these past several decades. Shorter irrigation runs, optimized furrow geometry, coupled with zero slope and proper inlet flows facilitate highly efficient application efficiencies and distribution uniformities in surface irrigation scenarios. Increased use of sprinklers in this region is another factor for improved water use efficiency. Additional further improvements in irrigation efficiency maybe limited by the risks of salts.

Research and outreach activities conducted in this region have resulted in improved N and P fertilization use efficiencies and corresponding reductions in N and P fertilizer use. Efficient irrigation has been paramount to our success with N management. Monitoring of surface and ground water show nitrate-N below health standards and phosphorus concentrations below levels of concern for aquatic ecosystems. In light of these observations, monitoring crop nutrient removal at the field levels within the BWD is not justified at this time. However, continued research and outreach activities aimed at further improvements in N and P fertilizer management are recommended. Monitoring should also continue but focus toward addressing existing data gaps. Monitoring of surface water is occurring by more than one public agency and the Bard Coalition efforts should address gaps in ground water data.

Levels of Mn in the drains do exceed California’s secondary standard of 0.05 mg/L but are below the health guidance level of 0.5 mg/L. The Mn in water is due the naturally high levels of Mn in the soil and not due to Mn fertilization. Levels in the Colorado River downstream of all agricultural discharge in the Yuma area are below the secondary standard. We did not observe any other inorganic constituent of concern.

Pesticide use is highly regulated at the state and federal levels. Pesticide applications are guided by scouting and are only applied in a manner consistent with the label. The irrigation systems utilized in the BWD do not allow for runoff of water into the drainage system thereby reducing risk of water contamination. However, detectable levels of a small subset of pesticides are found in the Colorado River downstream of BWD and agricultural production in this area may be a contributor in proportion to the acreage and discharge. However, all quantifiable levels of the few pesticides detected in surface water are well below existing public health and aquatic life benchmarks. Data on pesticides in ground water is less abundant but the data that does exists also shows no health concerns within the Bard area. However, due to a few detections downstream of BWD, some focused monitoring of selected pesticides in surface and ground water within BWD is recommended.

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1. BACKGROUND

1.1 Irrigated Land in the Lower Colorado River Region near Yuma

The Bard Water District (BWD) is part of the greater Yuma Agricultural community in that most farmers and employees working within the district reside in Yuma, business headquarters are located in Yuma, most agricultural inputs (seed, fertilizers, pesticides, fuel, etc.) are purchased in Yuma, and most agricultural products are processed and shipped from Yuma. This region includes seven organized irrigation entities all diverting water from the Colorado River and irrigating a total of 166,246 acres (Figure 1).

The irrigation entities east of the Colorado River within the former flood plains in Yuma County, Arizona, include the North Gila Irrigation District (NGID) east of the Colorado River and north of the Gila River at 6,320 acres, the Yuma Irrigation District (YID) south of the Gila River at 10,600 acres, Yuma County Water Users Association (YCWUA) south to the international border at 53,000 acres, and the Wellton Mohawk Irrigation and Drainage District east along the former flood plains of the Gila River at 62,750 acres. The Gila River typically does not flow into the WMIDD and all water used in this district is a Colorado River diversion. The Gila River does run west of the WMIDD due to agricultural drainage. Outside the former flood plains or valley districts, on the Yuma Mesa, are the Unit B Irrigation District at 3,400 acres and the Yuma Mesa Irrigation and Drainage District at 15,500 acres.

The BWD serves 14,676 acres west and north of the Colorado River in the southeastern portion of Imperial County, California. Approximately, 50% of the acreage served by the district is private land and 50% is native trust land associated with the Quechan Tribe. The private land within the BWD subject to regulation by the California Water Board is less than 5% of the total irrigated acreage in the region.

We wish to note that not all these organized entities are irrigation districts in a legal sense. The BWD is a state of California Water District and YCWUA is organized as a user’s association for operating the gravity conveyance system. However, for simplicity we will refer to all these organized entities as districts. Of these districts, YCWUA, BWD, Unit B, and a subset of NGID have beneficial use water rights and their allowed diversion is technically not quantifiable. All other districts (including the larger subset of NGID) have consumptive use rights and their diversion less return flows have a limit.

There are other irrigated agricultural areas outside of these seven districts including the Gila Monster Ranch north of the NGIDD, and a few other smaller enterprises with water contracts with the United States Bureau of Reclamation (USBR). There is also an area irrigated by wells south and east of YMIDD. Further, south of the Bard Unit and east of the Reservation Unit is an area known as the Yuma Island that once was east of the river before it changed course. After the river changed course a compromise among states split the state boundary within this area between California and Arizona. Most of the land is Arizona State Trust land (including that within the state of California) with long-term land leases granted to the descendants of the original settlers but some of the land is associated with the Quechan Tribe. With the exception

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of Ranch 5, associated with the Quechan Tribe, all farmland located on the Island is irrigated by wells since they have no surface water rights.

1.2 Bard Water District

The BWD came about as part of the United States Bureau of Reclamation (USBR) “Yuma Project” authorized in 1904 (Stene, 1996). The Yuma Project included the Valley Division in Yuma County, Arizona (currently YCWUA) and the Reservation Division in Imperial County, California. The Reservation Division was further split into the Bard Unit and the Indian Unit. Land in the Bard Unit was awarded to non-native homesteaders by lottery. The private landowners organized into the BWD in 1927. Diversions for the Yuma Project were initially facilitated through Laguna Dam. After 1948, all diversions from Laguna Dam were discontinued and were made from the Imperial Diversion Dam that was constructed as part of the Boulder Canyon Projects Act of 1928. At present, most land of the Indian Unit is leased to private farmers.

The canal delivery systems and the network of drains within the Bard Unit and the Indian Unit are comingled. Further, the BWD provides service to both units. The All American Canal runs along the NW end of the area serviced by the BWD and all diversions originate from this main canal (Figure 2). From the east, these diversions include the Reservation Main, Titsink, Yaqui, Pontiac, Yuma Main, and Ypsilanti canals. All these diversions are metered with gauges operated by the United States Geological Survey (USGS). The Yuma Main runs through the BWD in a southeasterly direction where its primary function is to transport water up to a siphon under the Colorado River and into YCWUA. However, there are some small diversions off the Yuma Main into the Bard service area. While these diversions are not monitored individually, the amount diverted combined with canal seepage can be estimated by difference from USGS metering gauges at the All American outlet and before the siphon under the Colorado River. About 50% of the canal distribution system within the BWD are concrete lined. The unlined canals would contribute seepage to the ground water. Further, the All American Canal and the Yuma Main Canal are not lined within the BWD service area and represent significant sources of water seepage in the area. The USBR monitors depth to ground water quarterly and the last report posted is from 2017 (USBR 2018). In the Reservation Division (Bard and Indian Units) data was collected from 124 monitoring wells and depth to ground water ranged from 1.5 to 48.1 ft with an average of 11.5 ft.

There are also a series of open drains within the Bard and Indian Units. The Bard Unit Coalition monitoring and reporting program focused on Drain 7, carrying drainage exclusively from private land and Drain 6 at a point that largely carries drainage from private land. The Imperial Irrigation District (IID) operates a series of drains parallel to the All American Canal largely aimed at mitigating seepage. In the NE two thirds of the Bard Service area these IDD drains ultimately flow into the Reservation Main Drain (Drain No. 4) which ultimately flows back into the river. For the SW one third, the drain parallel to the All American Canal becomes the Araz (Drain 8B) which also flows into the River. These are the only two drains that directly discharge into the river. The USGS monitors these return flows with gauges and the USBR

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collects samples every month for water quality testing. The water quality data will be addressed in a latter section.

1.3 Cropping Systems

The cropping systems in the BWD are diverse and similar to those in the other valley irrigation districts (NGID, YID, YCWUA, and WMIDD) in the Lower Colorado River region near Yuma (Table 1). All valley districts in the Yuma area, including BWD, have soils derived from river sediments deposited before dams, and largely consist of loam to silty clay loam soils. These valley districts are heavily skewed toward winter vegetable production. Multiple cropping is practiced, with two or more crops grown on a given field per year. For crops with large demand, such as iceberg lettuce and broccoli, fields can range from 20 to 40 acres in size but for many crops, such as the many of the leafy greens, individual planted area can be as less than 5 acres. Crops in the sequence do not necessarily share area. For example, a 20-acre field of wheat might be followed by several small 2 to 3 acre blocks of various mixed greens.

These cropping pattern are in contrast to the two districts on the Yuma Mesa (Unit B and YMIDD) which consist of sands, and are largely focused on citrus and alfalfa production. The BWD is not similar to Palo Verde Irrigation District (PVID) to the north and the IID to the west, located in Imperial County California. Most acreage in PVID and IID is associated with full season field crops such as alfalfa, grain, and cotton. The BWD may be unique compared to other districts in the Yuma area in that a larger proportion of the acreage is in dates palms. The BWD also participates in a summer fallow program facilitated through the Las Angeles Metropolitan Water District.

This Yuma region is the main production area for produce consumed in the United States in the late fall, winter, and early spring (Table 2). The range of crops grown are largely driven by contracts with national shippers (Dole, T&A, Foxy, Fresh Express, Taylor, etc.). These shippers typically contract with more than one grower, these growers typically grow for more than one shipper, and most growers farm in two or more of the aforementioned districts. The shippers own the mature crops and ultimately the shippers determine crop removal decisions. Weather, markets, and sometimes human health advisories influence the amount of crop removed by the shippers. There are conditions where weather adversely impacts quality and shippers may forego harvest on parts or entire fields. Weather may also cause a range of planting dates to mature at the same time creating short term over supply. Weather can also affect demand. When it is extremely cold in large parts of the U.S., demand for fresh produce declines and shipments north and east can be obstructed due to road conditions. Shippers may also pass over fields if market condition are such that crop value fails to cover harvest costs. It should also be noted that growers often section off larger 40 blocks for contracts with different shippers and different market destinations, further confounding crop removal decisions in a given area.

The other factor that affects crop removal is food safety advisories. For example, in fall 2018, there was an E, Coli outbreak in romaine lettuce and the FDA and CDC could not immediately isolate the source so they issued an advisory to halt the consumption of all romaine lettuce. Even after the outbreak was traced to a source outside the Yuma region, and the advisory was lifted, the

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demand for romaine remained low. During this period, multiple fields of romaine lettuce in the Yuma area were not harvested. 1.4 Return Flows

The USGS and USBR monitors flow in all the drains (and the Gila River) of the region that discharge into the Colorado River before the Northern International Boundary (NIB). The NIB is the point at which the river is no longer exclusively within the United States but is the shared border between Arizona and Baja, Mexico. This is in contrast to the Southern International Boundary (SIB) where the river leaves the United States and is entirely within Mexico. The NIB is an important reference point because diversion into Mexico takes place at the Morelos Diversion Dam immediately south of the NIB and water quantity and quality monitoring occurs at the NIB by the USBR, USGS, and the Internal Boundary and Water Commission. The river is typically dry south of the Morelos Diversion (all remaining water is diverted) and most monitoring at the SIB occurs at the Yuma Main Drain where this water also partially meets our treaty obligated deliveries to Mexico. In addition to measured return flows, there are substantial subsurface flows that the USBR estimates using mass balance methodology (Table 3). Unmeasured return flows are estimated by the difference between measured diversions less measured return flows and less estimated crop consumptive use. Traditionally, the USBR had used reported crop acreage estimates and the Blaney-Criddle ET model to estimate crop consumptive use (USGS, 1992). This remains an active area of research for the USBR and more recently they have implemented remote sensing as a tool to get better crop acreage estimates (USBR 2004; 2005) and improved ET models (Jensen, 1998). However, there remains some uncertainty in these measurements. For the past three years, we have operated a network of eddy covariance flux towers under a project partially funded by the USBR. Eddy Covariance is a methodology that uses energy balance to estimate crop ET. Data we have collected suggests crop coefficients currently used likely underestimate ET. Thus, current water balance methodology would over estimate unmeasured return flows. For this reason, I have declined to use unmeasured return flows in a quantitative context to estimate loading. However, these data would provide a reasonable estimate on the relative contribution of the various irrigated areas to total return since over-estimates would be similar across districts. In this estimate, we would have to exclude returns from the WMIDD into the Main Outlet Drain Extension (M.O.D.E), since this saline water bypasses the river system and is transported to the Santa Clara slough north of the Sea of Cortez. It would also have to exclude flows into the Gila Gravity Main Canal since this water is reused for irrigation. I also excluded measured flows in YCWUA, which all converge on the Yuma Main Drain and this crosses the international border becoming the Sanchez Mejorada Canal. In this estimate we also assigned 50% of the comingled unassigned flows associated with the Reservation Division, as well as those directly assigned to BWD, as BWD unmeasured returns. Using these assumptions we can conclude the BWD is approximately 10% of the return flows to the river in the region. There is also likely a mixing of ground water in the subsurface saturated zone among districts east and west of the river. A high profile example of this possibility is the PG&E hexavalent chromium plume near Topock, which occurred on the California side of the river, but the contaminant is also showing up in wells on the Arizona side of the river. The extent to which mixing of ground water east and west of the river occurs in the Yuma region is unknown.

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2. ON-FARM MANAGEMENT 2.1 Irrigation Management Improvements in water use efficiency associated with irrigation districts in the Yuma region has been the focus of a couple of recent publications (Brown et al., 2015; Frisvold et al. 2018) co-authored by the author of this report. The conclusions of these reports will be briefly summarized here but readers are referred to the original reports for more detail. Before I summarize the improvements, I wish to define indices of efficiency in irrigated agriculture (Burt et al., 1979). Irrigation efficiency (IE) is broadly defined as the water used by the crop consumptively (crop evapotranspiration or ETc) relative to that applied to the crops.

IE=ETc/Water Applied

This expression can have local (field level) or global (district-wide) ramifications. For a given field irrigation event this is equivalent to application efficiency (EA), which is the depth of water required relative to the amount of water applied.

Ea=Required Depth/Water Applied

The required depth is typically the amount of water required to offset soil water depletion resulting from crop evapotranspiration (ETc), but may also include a leaching fraction for salt management. We will discuss salt management in more detail in the next sub-section. It is important to note that application efficiency usually needs to be discussed concurrently with distribution uniformity (DU) which refers to how uniformly irrigation water is applied to a field. For example, field wide application efficiency may be high but if distribution uniformity is low, large parts of the field will be under-irrigated and/or over-irrigated, thereby compromising production. An example of application efficiency and distribution uniformity for a typical furrow irrigation scenario in the Yuma region is shown in Figure 3.

Another measure of efficiency is water use efficiency (WUE) which is marketable yield (Y) relative to ETc.

WUE=Y/ETc

As shown in figure 4, water use efficiency in Yuma region has increased substantially over the past several decades.

Beyond these simple considerations of efficiency, there are beneficial uses of water that may or may not be embedded into these expressions. We already noted salt management and that issue will be discussed in more detail in the next sub section. Pre-irrigation also hastens residue decomposition (such as wheat or cotton stubble) and provides moisture for seedbed preparation. This pre-irrigation water would be considered in a calculation of district wide efficiency but would generally not be considered in a calculation of individual crop water use efficiency.

Another beneficial use is water used for microclimate modification. For example, thermodormancy inhibits germination of lettuce and other vegetable crops. Water during stand establishment is not only to moisten seedbeds but also to reduce near surface soil temperatures in

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an effort to combat thermodormancy during late summer and early fall. However, as noted below, the use of sprinklers to modify climate has also resulted in large improvements is field level and district wide efficiencies. Water is also occasionally used for frost control. Irrigation immediately before a forecasted frost will increase heat capacity and thermal conductivity of near surface soils and increase the dew point within the crop canopy, providing some protection from frost damage.

Growers in all irrigation districts of the Yuma region, including the BWD, have adopted a number of improved technologies and cultural practices to improve irrigation management and efficiency. Laser leveling is a management technology that has been adopted by growers in all irrigation districts in the Yuma region. Laser leveling was introduced into the region over three decades ago, and currently all fields used for crop production are laser leveled to zero slope at minimum once a year. All surface irrigated vegetable crops in the Yuma area utilize impounded level furrows and most field crops use impounded level basins that do not allow for runoff (Erie and Dedrick, 1979) and improve efficiency (Howell, 2003; Sanchez et al., 2008a; 2008b). In these systems, all water is forced to infiltrate into the soil and there is no overland flow into the drainage system.

Field length along the irrigation run is another factor affecting water application efficiency and uniformity. While irrigation runs of 0.5 to 0.25 miles were not uncommon in the past, present day irrigation runs for vegetable crops seldom exceed 600 ft (0.125 miles less the ditches and field roads). Furrow geometry is another management practice that has been employed to improve water management. During the first cultivation after stand establishment, grower’s press the furrows into a tight trapezoidal configuration using an implement know as a “bola”. This trapezoidal configuration reduces friction and enables rapid movement of water down furrows. Overall, short runs, optimized furrow geometry, coupled with zero slope and proper inlet flows allow for highly efficient distribution uniformities and application efficiencies in surface irrigation scenarios (Sanchez et al., 2008a).

The use of sprinklers has been a major factor contributing to improved irrigation efficiency (Zerihun et al, 2014a 2014b; 2016a; 2016b). Two decades ago, vegetable crops were principally established by “subbing”. This practice involved running water in furrows until crop emergence, which typically took 7 to 10 days. Given that typical valley soils have a steady state water intake rate of 4 to 5 inches per day, estimates of the amount of water used for “subbing” range from 18 to 37 inches. Conversely, sprinklers used for crop establishment are typically run for 36 hours almost continuously, and thereafter, 4 to 6 hours per day as needed to keep the soil surface moist. The typical solid set sprinkler system used in the region delivers about 0.125 inches of water per hour. Given that a typical sprinkler system is operated for ~72 hours during crop establishment, the water required for crop establishment is reduced to less than 6 inches, with 3 inches of establishment water remaining in the top foot of soil and available for use by the crop (Table 4). There is little leaching fraction during stand establishment.

More recently, sprinklers have been used for season-long vegetable production. This is due to an increase in vegetables produced on 84-inch beds, including spring mix (lettuce and other leafy greens), spinach, and romaine hearts, where furrow irrigation is not possible. Sprinklers also are now routinely used to establish stands in wheat resulting in additional water savings. In a previous section, it was noted that soils in these valley districts trend toward silty clay loams.

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However, there are some lighter soils and these soils do present challenges in managing water and N efficiently. Thus, growers tend to put the season long sprinkler irrigated vegetable crops on these lighter soils where improved irrigation and N fertilization efficiencies can be achieved by sprinkler irrigation and fertigation..

In conclusion, irrigation efficiencies in the Yuma region, including the BWD have increased over the past decades and are high. It has been estimated that over 150,000 less acre -acre of water are drawn from the river partially due to the improvements discussed above (Brown et al., 2015).

2.2 Salt Management

In the arid southwest, irrigation water contains dissolved salts and water must be applied to leach salts that accumulate during crop evapotranspiration to maintain agricultural sustainability (Ayers and Westcott, 1985; Watson and Knowles, 1999). The salt sensitive crop in the rotational system typically dictates the leaching required (Sanchez and Silvertooth, 1996), and in the BWD, this is lettuce.

Required leaching is estimated using simple steady state salt mass balance (Ayers and Westcott, 1985). Using steady state assumptions, the average salinity of the Colorado River at the Imperial Diversion, and the tolerance of lettuce, a leaching requirement of 23% is required for maintenance. Thus, over a cropping season, 23% more water must be applied to these fields than crop ET.

This required leaching does not have to occur every irrigation event, provided salt buildup does not reach problematic levels during the cropping period. Growers in the Yuma region have sought to largely defer the required leaching to irrigation events outside the crop production period. This is evident in Figures 5 to 7, where data show net salt accumulation during the cropping periods. Their capability for doing this is enabled by the efficient irrigation technologies and practices described in section 2.1. This approach allows growers to more efficiently manage N in-season, avoid leaching of herbicides and soil insecticides below the crop root zone where efficacy is diminished, and mitigates crop disease. For this reason, a pre-irrigation in the late summer before produce is seeded in the fall, is typically practiced to restore salt balance.

Atmospheric evaporative demand is high in summer and water moves by capillarity from the underlying layers of the soil to the surface in the fine textured soils of the valleys (Figure 8). Water that evaporates from the surface leaves behind soluble salts that must be leached below the crop root zone to preclude salt damage to sensitive vegetable crops such as lettuce. Thus, even in summer fallow systems, pre-irrigation is required for sustainability (Figure 9).

Research regarding water and salt management is ongoing with funding from the Yuma Center of Excellence in Desert Agriculture (YCEDA), the Yuma County Agriculture Water Coalition (YCAWC) the USBR, the USDA, and several commodity organizations. We also have funding from NASA Jet Propulsion Laboratory and the Godard Space Flight center to develop user-friendly water and salt management tools supported by space based sensors. However, barring

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some innovation that mitigates salt, we see limited opportunities for further large improvements in irrigation efficiencies due to the fact we are near the limits for salt balance thresholds required for sustainability.

2.2 Fertilizer Management

The primary fertilizers used in the BWD, as in other districts in the Lower Colorado River region, are nitrogen (N) and phosphorus (P). The Universities of California and Arizona do not make a recommendation for potassium (K) in this region because the mineralogy of our soils are such that they generally provide adequate K, potassium is present in Colorado River water, and field experiments in the low desert fail to show a crop response to K (Unruh et al., 1994). Further, most other macronutrients and micronutrients are naturally present in soil and irrigation water in amounts adequate for optimal crop growth. The exception is zinc (Zn) where crops occasionally respond to Zn and we make Zn fertilizer recommendations based on soil tests.

Nitrogen fertilizer is universally used on all crops, except N fixing legumes, in the region. Our challenges are not unique and are similar to the daunting challenges faced by producers and agronomists globally. N fertilizer is required to meet the demand for food nationally and globally, and required for economic sustainability locally, but N fertilizer often has adverse environmental impacts on surface and ground water (Mosier et al., 2004), and is a source of a potent greenhouse gas, nitrous oxide (Hall et al., 1996). Nitrogen is chemically and biologically active in the natural environment and exists in multiple oxidation states. There are numerous possible fates of fertilizer applied N in addition to the desired outcome of crop uptake (Sanchez and Doerge, 1996; Havlin et al., 2005). The urea and ammonium components of the N fertilizer might be lost through ammonia volatilization. The nitrate-N might be lost to leaching with irrigation water below the crop root zone possibly impairing surface and ground water (Sanchez, 2000). Nitrate might also be lost as N2 and N2O gasses via de-nitrification processes (Bronson et al, 2018) affecting air quality and climate. Furthermore, the soil microbial population might immobilize inorganic N into the organic soil fraction where availability to crops is delayed.

Improvements in N use efficiency in agriculture systems has been a major focus of agricultural research over the past four decades. This is no less the case in California where a check off administered by the Fertilizer Research and Education Program (FREP) of the California Department of Food and Agriculture was implemented in 1990 aimed at improving fertilizer management in general and N management in particular. The author of this report has been the recipient of significant FREP funding since its inception and we have used this funding to conduct research and outreach in the Yuma region, including the BWD. At present, we have FREP funding to improve N management in spring mix cropping systems in the desert. There has been recent publications concerning expressions of N use efficiency Baligar et al., 2001; Dobermann, 2005; Erisman et al., 2018). These various expressions have been discussed in detail elsewhere and we refer readers to these publications for more detail. Briefly, the appropriate expression depends on the goal being sought. As with water, typically more than one expression of efficiency is often required to capture system productivity (yields as well as N recovery) and to address varying temporal and spatial scales of interest.

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A number of N fertilizer sources are used in the region but overwhelmingly the major source is Urea Ammonium Nitrate solution (UAN32) due to cost and efficacy. The urea in this source is rapidly hydrolyzed to ammonium (NH4) and the NH4 is rapidly oxidized to nitrate (NO3). In fact, due to our generally warm soil temperatures, all fertilizer N sources used in our region are quickly converted to NO3.

Because N is mobile, our strategies for improved efficacy have been aimed at timing applications such that they are synchronized with crop N demand (Sanchez and Doerge, 1999). This, strategy is aimed at increasing crop recovery and reducing leaching below the root zone. Elements of this strategy include split applications guided by tissue and soil testing. The increased irrigation efficiencies described in the previous section have also contributed to the success of this strategy.

We have also evaluated enhanced N efficiency products such as urease and nitrification inhibitors and controlled release fertilizers. While these products have found some application in our production system, they are not universally used. One major obstacle to the more widespread use of controlled release fertilizer is costs.

Through outreach activities throughout the region, including field demonstrations, we have had success in achieving enhanced N use efficiencies and N fertilizer use has declined. As part of this report we evaluated several databases on fertilizer use. The best database was reported by the USGS where they used fertilizer sales records taken from the Association of American Plant Food Control Officials fertilizer sales data, Census of Agriculture fertilizer expenditures, and U.S. Census Bureau county population (Gronberg and Spahr, 2012). Unfortunately, they only report through 2012. I filed an information request with the state of Arizona to get records from 2008 through 2018 to fill in the gaps but I had not received this data as of the writing of this report. We used data for Yuma County, AZ since all fertilizers used in the BWD are purchased in Yuma and the range of crops are similar. The data show a reduction in N use of 44% over a 10 year period (Figure 10). These observed trends are similar to data reported by others (USDA, 2019; USEPA, 2019)

Cool season vegetable crops produced in the Yuma region also typically receive large annual applications of phosphorus (P) fertilizer for optimal yield and quality. Amounts of P applied to these systems sometimes exceed 100 kg P/ha and crop recoveries of P fertilizers are generally less than 25% within the season of application (Sanchez 2007). Phosphorus fertilizer added to the calcareous agricultural soils in this region is rapidly converted to forms less available to plants through sorption and precipitation reactions. This process is often referred to as reversion because thermodynamics directs the added P toward mineral species similar to those found in mined phosphate, (Gowariker et al., 2009), forms typically not available to plants.

Phosphorus fertilizer use has been of global and national concern because P not used by crops or tied up by the soil is potentially transported downstream having adverse ecological effects on streams, rivers, lakes, and oceans (Dodds et al., 2009). While P movement to surface and ground water is less of a concern in our region, compared to other regions (Izuno et al.,1991), due to chemical tie up noted above, we have an active research program aimed at improving P fertilizer use efficiency due to other challenges. It is projected that P fertilizer costs will continue to

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increase due to declining P mineral reserves and the geopolitical distribution of these reserves (Cordell et al. 2009; Vaccari, 2009). The global P cycle is a long-term process in geologic time whereby P mineral deposits are distributed to terrestrial habitats by weathering, cycled through flora and fauna, carried to surface water and marine habitats by runoff, and by geologic processes, including tectonic uplift, P-enriched ocean sediments are deposited on land and the process begins anew (Filippelli, 2002). Exhausted P reserves are not replaced on a time line relevant to the needs of the current human population.

Our challenges with P fertilizer are not like those with N, in that our poor efficiencies are associated with chemical tie up and immobility. P moves in the soil by diffusion and timing is not an option for improved efficiency (Sanchez, 2007). Some future innovation that could reduce soil tie up of P would have profound impacts. Some products marketed claim those effects but our research has failed to show meaningful impacts among the products we evaluated. Over the past decades management practices, such as soil testing and improved fertilizer placement have been successfully exploited as tools to improve P fertilization efficiency (Sanchez, 2007). Through ancillary outreach programs, these management practices have been implemented throughout the region, including the BWD, and like N, P fertilizer use has declined (Figure 11).

Research aimed at improving N and P fertilizer use efficiency is ongoing and we will continue to exploit emerging technologies. Growers in the Yuma region have shown they embrace economically viable practices when they are available.

2.3 Pesticide Management

Pesticide use is highly regulated at the national and state levels in terms of when, what, how much, and methods of application. California Department of Pesticide Regulation regulates pesticide use in California and like the California Water Resources Control Board; it is an agency under the California Environmental Protection Agency (CalEPA). The pest control advisors (PCAs) serving growers in the BWD operate out of Yuma, serve growers across the Yuma region, and are certified in both states. These PCAs conduct scouting and make recommendations for pesticide applications based on economic thresholds, pesticide costs, efficacy, impacts on non-target organisms (beneficial insects) and resistance management considerations. In many cases, applications are contracted to commercial applicators that may or may not be affiliated with the PCA. In other cases, they are made by the grower. In all instances, training is required by law to apply pesticides.

Data bases compiled based on pesticide use reporting are broadly grouped by county. The range of crops produced in the BWD more closely resemble those used in the valley irrigation districts east of the Colorado River in Yuma County, Arizona than those in the Imperial Valley to the west. Therefore, the data shown in Table 5 are pesticide chemistries used in Yuma County Arizona on all land area exceeding 100 acres. It should be noted that in Arizona reporting is not required for unrestricted pesticides when they are applied by the grower. Thus, this database likely underestimates total pesticides applied.

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3. WATER QAULITY MONITORING

3.1 Fertilizer Nutrients

For evaluation of inorganic contaminants in surface water, I largely used existing USBR and USGS databases. Data collected by the USBR from 2009 to 2018 were requested and compiled for the Colorado River diversion at Imperial Dam, the Reservation Main, the Araz Drain, and the Colorado River at NIB. The chemistry of Araz Drain is largely influenced by seepage from the All American Canal so we focused on the Reservation Main Drain, which includes significant agricultural drainage. The data presented in Figure 12 show nitrate-N levels in the diversion at Imperial Dam, in the Reservation Main Drain and the NIB. Levels in the Reservation Main Drain are an indicator of the combined discharge from the BWD and the Indian Unit and are elevated, relative to the diversion, but remain well below the MCL of 10 mg/L. The levels at NIB are lower than discharge at the Reservation Main Drain but higher than water diverted at Imperial Dam. The levels at NIB would be a combined signature of all the discharges in the Yuma region diluted by water releases to Mexico for diversion at Morelos Dam. The data we complied from USBR data at NIB agree closely with the USGS monitoring (USGS NAWQA 2019). I also analyzed well water collected by the Bard Unit Coalition and all wells tested had nitrate-N levels less than 1 mg/L (Table 6).

With respect to phosphorus in water, there are no existing human health standards or objectives. USEPA does have some reference guidelines related to potential water treatment impacts and aquatic biological impacts. This guideline suggests P levels below 0.1 mg/L in flowing rivers and streams. For the USBR data sets I compiled, P is usually below their reporting levels; therefore, I used USGS data collected at the NIB. All levels are well below 0.1 mg/L. We would not expect significant P transport because our irrigation systems do not allow overland flow into the drainage network and our soils have a high propensity to chemically tie-up P.

Although our efforts in improving N and P use efficiencies are a work in progress, there have been considerable gains in the past two decades. Data show N and P fertilizer use is declining. Further, N in surface and ground water and P in surface water are below thresholds of human health and ecological concerns. For these reasons, monitoring crop removal of nutrients is not recommended at this time. This would be an onerous and costly undertaking in BWD due to the complex cropping patterns, and the crop removal decisions not controlled by the growers, that are noted in section 1.3, and would have no net positive impact on the environment.

3.2 Other inorganics

There are other inorganics elements of concern to USEPA and CalEPA. California has an MCL for fluoride of 2 mg/L and a public health goal of 1 g/L. The levels in all surface waters evaluated are below 1 mg/L (Table 7). There are also several metal elements for which California has established MCLs. While I have not sampled the drains, I have sampled the river at Imperial Diversion and the NIB. All levels are below California’s MCLs and are not altered significantly by irrigation discharge (Table 8).

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There are also a number of secondary standards (Table 7). Secondary standards are not based on health concerns but set for aesthetic considerations. While these secondary standards are not enforced by USEPA, they are enforced in California. Many of the salinity related secondary standards (conductance, TDS, and sulfate) are exceeded in the river prior to diversion, and are further concentrated in the drain water (Table 7 and Figure 14). This is not surprising as a key component of our irrigation management strategies are to remove salts which concentrate in soil water due to evapotranspiration.

There are also secondary standards for Mn and Fe. All surface waters tested the below secondary standard for Fe of 0.3 mg/L. The Mn concentrations in the drains do exceed the secondary standard of 0.05 mg/L. The soils in the region have a number of metals naturally present in the parent material (Table 9). We suspect transitory anaerobic conditions during irrigation or anaerobic sites in the soil subsurface facilitate the reduction of Mn from insoluble oxide forms to more soluble reduced forms.

The potential human health impacts of Mn have been evaluated (ATSDR, 2008). Manganese is an essential nutrient but the threshold between beneficial and potential problematic intakes is narrow. There may be nutritional benefits to intakes as high as 7 mg/day but doses exceeding 10 mg/day may affect certain sub populations. A reference dose (RfD) of 0.14mg/kg-day has been established which is equivalent to the no observed adverse effect level (NOAEL). The state of California has established a drinking water health guidance level of 0.5 mg/L (10x times the secondary standard) and concentrations in the drains remain below this. It should be noted, that the measured Mn levels in the Colorado River at the NIB, a potential drinking water source in Mexico, are even below the secondary standard of 0.05 mg/L.

The California Water Boards have compiled a list of wells exceeding 0.5 mg/L and two are in Winterhaven, CA. close to Bard (CWRCB, 2019). East of the river in Yuma County AZ, Mn is also frequently found in ground water at levels exceeding 0.5 mg/L (Towne and Yu, 1998). It is our intension to provide Mn data for the 12 wells samples collected by the Bard Coalition Group shown in Table 6 for NO3-N but the analysis were not complete as of the writing of this report. Manganese is not used as a fertilizer locally because it is present in the soil in abundant amounts. There is no evidence that agriculture practices even unrelated to Mn fertilization (cultivation, irrigation, etc.) increase Mn concentrations in ground water. In fact, one study in Yuma County, AZ, included wells in undeveloped desert land and statistical analysis showed no significant trend in water quality parameters to land use (Towne and Yu, 1998). This study did provide evidence that Mn is associated with soil and minerals in that those Mn concentrations were statistically higher in the ground water below the fine-textured valley soils than the coarse textured mesa soils. Furthermore, within these areas, Mn concentrations were statistically higher in fine-grained sampling zones than the coarse grain sampling zones.

Another concern in California is perchlorate. The Colorado River is contaminated via the Las Vegas Wash, near Henderson NV, from a plant that manufactured ammonium perchlorate for the munitions and aerospace industries (Sanchez et al, 2009). Perchlorate in the river does not exceed the California MCL of 0.006 mg/L and is decreasing due to cleanup efforts on the Las Vegas Wash. Chilean nitrate fertilizer is also a known source of perchlorate. However, there is

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no history of widespread Chilean nitrate fertilizer use in the Yuma region and isotope ratio analysis confirms the perchlorate in the river is derived from the source near Henderson, NV (Bohlke et al., 2005).

3.3 Pesticides

Pesticides in surface and ground waters were evaluated using public databases. For surface water, one particular data set relevant to the BWD is a sample collection on the Reservation Main in 2002 collected by the WQRCB Surface Water Ambient Sampling Program (SWAMP). Although 16 years old, in 2002 water was tested for 37 pesticide chemistries and sediments for 10 chemistries on two dates (May 9 and October 2). Of the chemistries tested in the program, a subset are currently used by the agricultural industries in the Yuma region (Table 5). All samples were below detection limits.

The other significant surface water databases were collected by the USGS as part of their National Water Information System (NWIS) monitoring program (USGA NAWQA, 2019). These samples were collected at the NIB and any measured impacts would not exclusively apply to BWD, but reflect all discharges into the river in the Yuma region. This program included evaluation of 215 pesticide chemistries between 2008 and 2017. The data for 2018 were not posted as of the writing of this report. Of all the chemistries evaluated, 13 were at detectable levels. I wish to highlight a few observations from this data. First, atrazine and diuron were consistently detected at NIB at quantifiable levels. Interestingly, atrazine is not widely used in the Yuma area. Although wheat is a common crop in the region, the plant back restrictions for atrazine would not allow most crops we grow in rotation with wheat. One of the most widely, used herbicides in the area propyzamide, was rarely detected.

Many of the insecticides used on large acreages in the Yuma region are generally not detected. Some examples include methomyl, permethrin, bifenthrin, indoxacarb, dicamba, and malathion. Chlorpyrifos and diazinon were occasionally detected but these two pesticides also have uses outside of agriculture. It should be stressed that of the 13 chemistries detected at NIB, 11 had human health and aquatic life benchmarks and all these 11 were below these benchmarks.

One that seems to be detected with increasing frequency is imidacloprid. This observation is consistent with other reports. In 2012, one study reported finding imidacloprid in 89% of the samples collected in California, some in quantities exceeding thresholds for chronic toxicity for aquatic invertebrates of 1.05 ug/L (Starner and Kean, 2012). The levels at NIB remain an order of magnitude below this aquatic benchmark. A drinking water MCL for imidacloprid has not been established but a chronic reference dose of 0.057 mg/kg-day has. If we assume the usual reference body weight and water consumption volume assumptions, and a relative source contribution of 20%, we estimate a hypothetical guidance level of 0.4 mg/L, orders of magnitude above the highest levels ever detected at NIB. However, imidacloprid is currently on the ground water protection list and follow up sampling specifically in the BWD may be warranted.

Data for ground water is more limited. There are 14 wells in the Bard area that have been occasionally tested for pesticides over the past 25 years (Table 10). Only a subset of the chemistries are among those currently used in the Yuma region. Among this data, the most

http://water.usgs.gov/nawqa/

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current are the three wells tested by CSWRCB in 2007. A few wells were re-sampled again in 2013 for thiobencarb. Overall, with the exception of two chemistries, all samples were below detection. One notable exception is well 8706 where hexazinone was quantifiable on water collected in 1987. This broad-spectrum herbicide would not be used for the cropping systems in Bard. Further, it was found in a well within a suburban business complex. This chemistry was not detected in any other wells and was not likely related to agricultural use. There was also a detectable but not quantifiable level of prometryn in one domestic well sampled in 2007 but this was not detected in any other well and is infrequently detected at NIB. An older study conducted east of the river in Yuma County, AZ also showed no detectable pesticides in ground water of 157 chemistries tested (Towne and Yu, 1998). Although much of these data from wells in the region are not current, they show that there is not a history of pesticides moving into the ground water in the region. Overall, the surface and ground water samples collected, and associated with Bard, do not show problematic levels of pesticides moving into water.

3.4 Emerging Contaminants

Agricultural areas would not normally be a source of emerging contaminants (ECs) including pharmaceuticals, illicit drugs, and personal care products. These are usually associated with urban waste streams. This was an area of research because we were concerned about food chain transfer if they were present in irrigation water. We have identified ECs in more than one urban discharge on the Colorado River (Jones et al., 2012). However, these products are seldom detected downstream from the discharge into the river. None of the ECs evaluated were found in crops irrigated with Colorado River water (Jones et al., 2010).

Literature Cited ATSDR, 2008, Toxicological Profile for Manganese, Agency for Toxic Substances and Disease Registry, September 2008.

Ayers R. S., and D. W. Westcott. 1985. Water Quality for Agriculture. FAO Irrigation and Drainage paper No. 29. http://www.fao.org/DOCReP/003/T0234e/T0234E03.htm Baligar V. C., N. K. Fageria, and Z. L. He. 2001. Nutrient use efficiency in plants. Comm.Soil Sci. Plant Anal. 32:921-950, DOI: 10.1081/CSS-100104098 Bohlke, J. K., N. C. Sturchio, B. Gu, J. Horita, G. M. Brown, W. A Jackson, J. Batista, and P. B. Hatzingerr. 2005. Perchlorate Isotope Forensics. Anal. Chem. 77: 7838-7842. Bronson, K. F., D. J. Hunsaker, C. F. Williams, K. R. Thorp, S. M. Rockolt, S. J. Del Grosso, R. T. Venterea, and E. M. Barnes. 2018. Nitrogen management affects nitrous oxide emissions under varying cotton irrigation systems in the desert southwest USA. J. Environ. Qual. 47:70-78. Brown, P.W., K. D., Nolte, and C. A. Sanchez, C.A. 2015. Irrigation Management in Yuma County. In “A Case Study in Efficiency—Agriculture and Water Use in the Yuma”; Yuma

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County Agricultural Water Coalition: Arizona Area, Yuma, AZ, USA, 2015; pp. 17–49. Available online: http://www.agwateryuma.com/ . Burt, C. M., A.J. Clemmens, T.S. Strelkoff, K.H. Solomon, R.D. Bliesner, L.A. Hardy, T.A. Howell, and D.E. Eisenhauer. 1997. Irrigation performance measures: efficiency and uniformity. J. Irrig. Drain. Eng., 123(6): 423-442. Cordell, D., J. O. Drangert, and S. and White. 2009. The story of phosphorus: Global food security and food for thought. Global Environmental Change. 19(2): 292–305.

CWRCB. 2019. Drinking Water Notification Level for manganese. https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/Manganese.html Dobermann, A R. 2005. "Nitrogen Use Efficiency – State of the Art" Agronomy & Horticulture -- Faculty Publications. 316. http://digitalcommons.unl.edu/agronomyfacpub/316 Dodds W.K., W. W. Bouska, J. L. Eitzmann, T. J. Pilger, K. L. Pitts, A. J. Riley J. T. Schloesser and D. J. Thornbrugh. 2009. Eutrophication of U.S. freshwaters: analysis of potential economic damages. Environ. Sci. Technol. 43:12–19. Erie, L. J. and A.R. Dedrick. 1979. Level Basin Irrigation: A Method for Conserving Water and Labor. USDA SEA Farmers’ Bulletin 2261. 23p. Erisman, J., A. Leach, A. Bleeker, B. Atwell, L. Cattaneo, and J. Galloway. 2018. An Integrated Approach to a Nitrogen Use Efficiency (NUE) Indicator for the Food Production–Consumption Chain. Sustainability 10: 925. Filippelli G. M. 2002. The global phosphorus cycle. In: Kohn M, Rakovan J, HughesJ (eds) Phosphates: Geochemical,Geobiological, and Materials Importance. Reviews in Mineralogy & Geochemistry 48: 391-425. Frisvold, G., C. A. Sanchez, N. Gollehon, S. B. Megdal, and P. Brown. 2018. Evaluating Gravity-Flow Irrigation with Lessons from Yuma, Arizona, USA Sustainability. 10(5):1548. https://doi.org/10.3390/su10051548 Gronberg, J.M., and N. E. Spahr. 2012, County-level estimates of nitrogen and phosphorus from commercial fertilizer for the Conterminous United States, 1987–2006: U.S. Geological Survey Scientific Investigations Report 2012-5207, 20 p. Gowariker V, V. N. Krishnamurthy, S. Gowariker, M. Dhanorkar, and K. Paranjape. 2009. The Fertilizer Encyclopedia. John Wily & Sons, Hoboken, NJ Hall, S.J., P.A. Matson, and P.M. Roth. 1996. NOx emissions from soil: Implications for air quality modeling in agricultural regions. Annual Review of Energy and the Environment 21:311-346.

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Havlin, J., S., L. Tisdale, J. D. Beaton, and W.L. Nelson. 2005. – Soil Fertility and Fertilizers, 7th Edition. Pearson Prentice Hall, NJ. Howell, T.A. 2003. Irrigation efficiency. In: B.A Stewart and T.A. Howell (ed). Encyclopedia of Water Science: 467-472. Marcel Dekker, Inc., New York. Izuno, F. T., C. A. Sanchez, F. J. Coale, A. B. Bottcher, and D. B. Jones. 1991. Phosphorus concentrations in drainage water in the Everglades Agricultural Area. J. Environ. Qual. 20:608-619. Jensen, M. E., 1998. "Coefficients for Vegetative Evapotranspiration and Open-Water Evaporation for the Lower Colorado River Accounting System," October 1998, Fort Collins, CO (available from the Bureau of Reclamation, Boulder Canyon Operations Office, Boulder City, Nevada). Jones-Lepp,T. L. C. A. Sanchez, D. A Alvarez, D. C Wilson, and R. Taniguchi-Fu. 2012. Point sources of emerging contaminants along the Colorado River Basin: Source water for the arid Southwestern United States. Sci. Total Environ. 15:430:237 Jones-Lepp, T. L., C. A. Sanchez, T Moy, and R. Kazemi. 2010. Method development and application to determine potential plant uptake of antibiotics and other drugs in irrigated crop production systems. J. Agric. Food Chem. 58:11568-11573. Mosier, A. R, Syers, J. K., and Freney, J. R. 2004. Nitrogen fertilizer: An essential component of increased food, feed, and fiber production. Pages 3-18 in: SCOPE 65: Agriculture and the Nitrogen Cycle: Assessing the Impacts of Fertilizer Use on Food Production and the Environment, A. R. Mosier, J. K. Syers, and J. R. Freney, eds. Island Press, Washington, DC. Sanchez, C.A. 2000. Response of lettuce to water and N on sand and the potential for leaching of nitrate-N. HortScience 35:73-77.

Sanchez, C. A. 2007. Phosphorus. In A. V. Barker and D. J. Pilbeam (eds.). Handbook of Plant Nutrition CRC Press. Taylor and Francis, Boca Raton, FL, pp 51-90. Sanchez, C. A., and T. A. Doerge. 1999. Using nutrient uptake patterns to develop efficient nitrogen management strategies for vegetables. HortTechnology 9:601-606. Sanchez, C. A., and J. C. Silvertooth. 1996. Managing saline and sodic soils for the production of horticultural crops. HortTechnology 6:99-107. Sanchez, C. A., L. M. Barraj, B. C. Blount, C. G. Scrafford, L. Valentin-Blasini, K. M. Smith,and R. I. Krieger. 2009. Perchlorate exposure from food crops produced in the lower Colorado River region. J. of Exposure Sci. and Environ. Epidemiology 19:359-368. Sanchez, C. A., D. Zerihun, and K. L. Farrell-Poe. 2008a. Management guidelines for efficient irrigation of vegetables using closed-end level furrows. Agric.Water Management. 96:43-52.

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Sanchez, C.A., D. Zerihun, T. S. Strelkoff, A. J. Clemmens, A. J., and K. L. Farrell-Poe, 2008b. Development of management guidelines for efficient irrigation of basins on sandy soils. Appl. Eng. Agric. (ASABE) 24(2):1-10. Starner, K, and K. S. Goh, Kean. 2012. Detections of Imidacloprid in Surface Waters of Three Agricultural Regions of California, USA, 2010-2011. Bulletin of Environmental Contamination and Toxicology. 88 (3): 316–321. Stene, Eric. 1996. Yuma Project and Yuma Auxiliary. https://www.usbr.gov/projects/pdf.php?id=212

Towne, D. C., and W. K. Yu. 1998. Ambient ground water quality of the Yuma Basin. A 1995 Baseline Study. Arizona Department of Environmental Quality. September 1998. OFR 98-7.

Unruh, B. L., J. C. Silvertooth and D. M. Hendricks. 1994. Potassium fertility status of several Sonoran Desert soils. Soil Sci. 158:435 -441. USDA. 2019. USDA National Agricultural Statistics Office-Arizona Office. https://www.nass.usda.gov/Statistics_by_State/Arizona/index.php (accessed April 2019) USEPA, 2019. Commercial fertilizer purchases https://www.epa.gov/nutrient-policy-data/commercial-fertilizer-purchased (accessed April 2019) USBR. 2019. Lower Colorado River Water Accounting. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwje07j2qZniAhWhilQKHRNGDcAQFjAAegQIBBAB&url=https%3A%2F%2Fwww.usbr.gov%2Flc%2Fregion%2Fg4000%2Fwtracct.html&usg=AOvVaw21YzgD0av3Yx6NGEeU8tXK USBR. 2004. Lower Colorado River Accounting System Evapotranspiration and Evaporation Calculations. Calendar Year 2004. https://www.usbr.gov/lc/region/g4000/4200Rpts/LCRASRpt/2004/Report04.pdf USBR. 2005. Lower Colorado River Accounting System Evapotranspiration and Evaporation Calculations. Calendar Year 2004. https://www.usbr.gov/lc/region/g4000/4200Rpts/LCRASRpt/2005/Report05.pdf USBR. 2018. 2017 Ground Water Status Report Yuma Area Arizona and California. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=2ahUKEwi70diJgZbiAhWWhJ4KHW0aB6MQFjABegQIARAC&url=https%3A%2F%2Fwww.usbr.gov%2Flc%2Fyuma%2Fprograms%2FYAWMS%2FReports%2F2017%2520Groundwater%2520Status%2520Report_Final.pdf&usg=AOvVaw1IWWGr6svVqLaJ0i_6Wue8

USGS. 1992. Accounting system for water used by vegetation in the lower Colorado River region, Water Fact Sheet. Open File Report 92-83. https://pubs.usgs.gov/of/1992/0083/report.pdf

https://www.usbr.gov/projects/pdf.php?id=212https://www.nass.usda.gov/Statistics_by_State/Arizona/index.phphttps://www.epa.gov/nutrient-policy-data/commercial-fertilizer-purchasedhttps://www.epa.gov/nutrient-policy-data/commercial-fertilizer-purchasedhttps://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwje07j2qZniAhWhilQKHRNGDcAQFjAAegQIBBAB&url=https%3A%2F%2Fwww.usbr.gov%2Flc%2Fregion%2Fg4000%2Fwtracct.html&usg=AOvVaw21YzgD0av3Yx6NGEeU8tXKhttps://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwje07j2qZniAhWhilQKHRNGDcAQFjAAegQIBBAB&url=https%3A%2F%2Fwww.usbr.gov%2Flc%2Fregion%2Fg4000%2Fwtracct.html&usg=AOvVaw21YzgD0av3Yx6NGEeU8tXKhttps://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwje07j2qZniAhWhilQKHRNGDcAQFjAAegQIBBAB&url=https%3A%2F%2Fwww.usbr.gov%2Flc%2Fregion%2Fg4000%2Fwtracct.html&usg=AOvVaw21YzgD0av3Yx6NGEeU8tXKhttps://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwje07j2qZniAhWhilQKHRNGDcAQFjAAegQIBBAB&url=https%3A%2F%2Fwww.usbr.gov%2Flc%2Fregion%2Fg4000%2Fwtracct.html&usg=AOvVaw21YzgD0av3Yx6NGEeU8tXKhttps://www.usbr.gov/lc/region/g4000/4200Rpts/LCRASRpt/2004/Report04.pdfhttps://www.usbr.gov/lc/region/g4000/4200Rpts/LCRASRpt/2005/Report05.pdfhttps://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=2ahUKEwi70diJgZbiAhWWhJ4KHW0aB6MQFjABegQIARAC&url=https%3A%2F%2Fwww.usbr.gov%2Flc%2Fyuma%2Fprograms%2FYAWMS%2FReports%2F2017%2520Groundwater%2520Status%2520Report_Final.pdf&usg=AOvVaw1IWWGr6svVqLaJ0i_6Wue8https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=2ahUKEwi70diJgZbiAhWWhJ4KHW0aB6MQFjABegQIARAC&url=https%3A%2F%2Fwww.usbr.gov%2Flc%2Fyuma%2Fprograms%2FYAWMS%2FReports%2F2017%2520Groundwater%2520Status%2520Report_Final.pdf&usg=AOvVaw1IWWGr6svVqLaJ0i_6Wue8https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=2ahUKEwi70diJgZbiAhWWhJ4KHW0aB6MQFjABegQIARAC&url=https%3A%2F%2Fwww.usbr.gov%2Flc%2Fyuma%2Fprograms%2FYAWMS%2FReports%2F2017%2520Groundwater%2520Status%2520Report_Final.pdf&usg=AOvVaw1IWWGr6svVqLaJ0i_6Wue8https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=2ahUKEwi70diJgZbiAhWWhJ4KHW0aB6MQFjABegQIARAC&url=https%3A%2F%2Fwww.usbr.gov%2Flc%2Fyuma%2Fprograms%2FYAWMS%2FReports%2F2017%2520Groundwater%2520Status%2520Report_Final.pdf&usg=AOvVaw1IWWGr6svVqLaJ0i_6Wue8https://pubs.usgs.gov/of/1992/0083/report.pdf

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USGS. 2019. National Water-Quality Assessment (NAWQA). 2019. https://cida.usgs.gov/quality/rivers/technical_information Vaccari, D. A. 2009. Phosphorus-A looming crisis. Sci. Amer. 54:59. Watson, J. and T. Knowles. 1999. Leaching for Maintenance. Factors to Consider for Determining the Leaching Requirement for Crops. 5/99. AZ1107. Arizona Water Series • Number 22. https://extension.arizona.edu/pubs/az1107.pdf Zerihun, D., C. A. Sanchez, and K Nolte. 2014a. Field-Scale Sprinkler Irrigation System Hydraulic Model. I: Hydraulic Characterization. J. Irrig. Drain Eng., 140: Zerihun, D. and C. A. Sanchez. 2014b. Field-Scale Sprinkler Irrigation System Hydraulic Model. II: Hydraulic Simulation. J. Irrig. Drain Eng. 10.1061/(ASCE)IR.1943-4774.0000723, 04014020. Zerihun, D., C. Sanchez, A. and Warrick. 2016a. Sprinkler Irrigation Droplet Dynamics. I: Review and Theoretical Development. J. Irrig. Drain Eng., 10.1061/(ASCE)IR.1943-4774.0001003, 04016007. Zerihun, D., C. Sanchez, and A. Warrick. 2016b. Sprinkler Irrigation Droplet Dynamics.II: Numerical Solution and Model Evaluation. J. Irrig. Drain Eng., 10.1061/(ASCE)IR. 1943- 4774.0001004, 04016008.

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List of Tables

Table 1. Reported crop acreage in BWD in 2016 and 2017.

Table 2. Crop grown in lower Colorado River region and percentage of total US production.

Table 3. Measured and unmeasured return flows to the Colorado River in the Yuma region in 2016 to 2018. Table 4. Water balance and salt load during sprinkler stand establishment in Yuma area.

Table 5. Pesticide chemistries applied on all acreage over 100 acres in Yuma County, Arizona in 2016 through 2018.

Table 6. Maximum regulatory standards set by California EPA and measured levels of inorganic contaminants in water. Table 7. Nitrate-N levels in selected wells in the BWD. Table 8. Average metal concentration at Imperial Diversion Dam and NIB compared to Cal EPA

maximum contaminant levels. Table 9. Summary of wells tested for pesticides in Bard area including Bard Unit, Indian Unit, and Yuma Island.

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List of Figures

Figure 1. Water Diversion entities in the Lower Colorado River region near Yuma.

Figure 2. Irrigation delivery and drainage system in BWD.

Figure 3. Application efficiency and low-quarter distribution uniformity expressed as a function of furrow inflow rate and cutoff time for medium textured soil in Yuma area. Figure 4. Water use efficiency (WUE) for lettuce in Yuma region over the past decades.

Figure 5. Field wide salinity before and after lettuce in YCWUA 16-17.

Figure 6. Field wide salinity before and after wheat in BWD 17-18. Figure 7. Change in average field salinity across cropping systems. Lettuce-wheat is the most common rotation in the region. Figure 8. Evaporation measured by Eddy Covariance methodology during summer 2017 fallow

period. Figure 9. Field wide salinity before summer fallow, after summer fallow, and after pre-irrigation for BWD site. Figure 10. Agricultural N use trend in Yuma County 2003 to 2012.

Figure 11. Agricultural P fertilizer use trends in Yuma County 2003 to 2012.

Figure 12. Measured nitrate-N in Diversion, Reservation Main, and NIB from 2009 to 2018.

Figure 13. Measured soluble and total P at NIB.

Figure 14. Average conductance of water in Diversion, Reservation Main, and NIB from 2009 to 2018.

Table 1. Reported Crop acreage in BWD in 2016 and 2017.

Crop Year and acreage

2016 2017 Alfalfa 48 48 Barley 14 12

Broccoli 1309 1168 Bermuda grass 36 36

Cabbage 26 12 Cauliflower 625 421

Celery 495 334 Cilantro 350 305 Citrus 210 326 Cotton 745 603 Dates 1,100 1455 Fennel 87 65

Mixed greens 110 60 Napa 60 17

Lettuce 3764 3005 Okra 63 31 Onion 236 201 Parsley 38 21 Pecans 10 10 Spinach 38 23

Sugar beet 33 0 Sudan grass 1928 1712 Watermelon 79 39

Wheat 2490 2303 Acreage for 2018 was not compiled as of the writing of this report.

Table 2. Crop grown in lower Colorado River region and percentage of total US production.

Crop Area of Production on low desert (acres)

Acres in low desert as a percentage of total US

crop (%) Broccoli (Brassica oleracea italica) 23,504 18 Cabbage (Brassica oleracea capitata) 2,475 4.6 Carrots (Daucus carota sativus) 17,858 28 Cauliflower (Brassica oleracea botrytis) 8,965 25.6 Celery (Apium graveolens) 1,428 4.3 Dates (Phoenix sylvestris) 7,228 100 Lemon (Citrus limon) 17,507 32.1 Lettuce Head (Lactuca sativa) 63,429 32.9 Lettuce Leaf (Lactuca sativa) 52,514 45.8 Melon (Cucumis melo) 13,809 15.2 Watermelon (Citrullus lanatus) 3,865 4.7

Data compiled from USDA data sources. Lower Colorado River region included Yuma County Arizona, and Riverside and Imperial Counties California. Yuma is the larger of these areas of production.

Table 3. Measured and unmeasured return flows to the Colorado River in the Yuma region in 2016 to 2018.

State and Area Return Flow 2016 2017 2018 Arizona

NGID Measured 24,969 25,501 24,842 Unmeasured 5,883 6,160 5,699

YID Measured 17,433 15,802 16,487 Unmeasured 15,010 13,360 13,892

WMIDD Measured GGMC 21,462 19,875 17,218 Measured Dome 6,059 5,426 5,911 Measured MODE 99,130 101,064 104,210 Unmeasured 0 0 0

YCWUA Measured 119,433 116,007 96,802 Unmeasured 7346 7,168 7,205

YMIDD Measured 44,124 42,247 57,680 Unmeasured 30,808 31,559 36,632

Unit B Measured 7,331 6,965 9,230 Unmeasured 0 0 0

City of Yuma Measured 10,355 9795 10,095 Unmeasured 11 0 0

Arizona State Land Measured 110 121 nd Unmeasured 3,928 4,107 nd

Ft Yuma Reservation Measured 0 0 nd Unmeasured 608 611 nd

Cocopah Reservation Measured 7 15 15 Unmeasured 917 799 252

Othersa Measured 329 364 nd Unmeasured 4405 4,608 nd

California Yuma Project Reservation Division

Indian Unit Measured 1034 731 530 Unmeasured 7612 7,554 7.116

Bard Unit Measured 669 381 292 Unmeasured 7968 6,343 7,156

Unassigned Measured 0 0 0 Unmeasured 28407 23,296 26,656

Other Ft Yuma Ranches 1 through 17 Measured 0 0 nd

Unmeasured 1994 1,338 nd Other

Yuma Island (AZ State Trust) Measured 0 0 nd Unmeasured 2746 1,795 nd

City of Winterhaven Measured 0 0 nd Unmeasured 34 32 nd

aSeveral small water contractors are combined in this table. For specifics refer to USBR accounting reports.

nd=no data. Data processing for some sites in 2018 were not complete as of the writing of this report.

MODE is Main Outlet Drain Extension. GGMC is Gila Gravity Main Canal.

Table 4. Water balance and salt load during sprinkler stand establishment of vegetables in Yuma area.

Site Wet Date

Soil Moisture Deficit (inches)

Last Sprinkler Run Date

Water Received (inches)

Irrigation Water

(tons/A)

Leaching Fraction

Soil salts to 12 inches (tons/acre)

Soil salts to 18 inches (tons/acre)

Before After Before After

YID1 Sept. 11 -3.4 Sept. 15 5.0 0.5 0.30 1.2 1.0 3.8 4.4 YID2 Sept. 12 -3.5 Sept. 16 4.8 0.5 0.24 1.2 1.3 4.5 4.8 WMID 1 Sept. 11 -3.4 Sept. 16 4.4 0.5 0.05 1.2 1.2 3.3 4.0 WMID 2 Sept. 12 -3.1 Sept. 18 5.2 0.6 0.27 0.9 1.1 3.1 4.0 WMID 3 Sept. 13 -3.1 Sept. 18 4.3 0.4 0.13 1.0 1.1 3.2 5.6 BWD 1 Sept. 12 -4.1 Sept. 20 3.5 0.5 0 1.2 1.6 3.6 5.3

Unpublished data of Sanchez et al.

Table 5. Pesticide chemistries applied on all acreage over 100 acres in Yuma County, Arizona in 2016 through 2018.

Date

2016 2017 2018

ACTIVE INGREDIENT CHEMICAL CLASS TOTAL ACRES

ACTIVE INGREDIENT CHEMICAL CLASS TOTAL ACRES

ACTIVE INGREDIENT CHEMICAL CLASS TOTAL ACRES

SPINETORAM (AMIXTURE OF SPINETORAM-J AND SPINETORAM-L)

SPINOSYN 160927 SPINETORAM (AMIXTURE OF SPINETORAM-J AND SPINETORAM-L)

SPINOSYN 154138 SPINETORAM (AMIXTURE OF SPINETORAM-J AND SPINETORAM-L)

SPINOSYN 129432

LAMBDA-CYHALOTHRIN PYRETHROIDS PYRETHRINS

140637 LAMBDA-CYHALOTHRIN PYRETHROIDS PYRETHRINS

119547 LAMBDA-CYHALOTHRIN PYRETHROIDS PYRETHRINS

110173

PERMETHRIN PYRETHROIDS PYRETHRINS

104574 MONO- AND DI- POTASSIUM SALTS OF PHOSPHOROUS ACID

INORGANIC 101140 MONO- AND DI- POTASSIUM SALTS OF PHOSPHOROUS ACID

INORGANIC 85219

MONO- AND DI- POTASSIUM SALTS OF PHOSPHOROUS ACID

INORGANIC 82683 PERMETHRIN PYRETHROIDS PYRETHRINS

91882 PERMETHRIN PYRETHROIDS PYRETHRINS

79215

DIMETHOMORPH CINNAMIC ACID AMIDES

51756 DIMETHOMORPH CINNAMIC ACID AMIDES

64393 DIMETHOMORPH CINNAMIC ACID AMIDES

49503

PROPYZAMIDE AMIDE 47886 FENAMIDONE IMIDAZOLINONES 54719 MANDIPROPAMIDE MANDELAMIDE 43714

CHLORANTRANILIPROLE DIAMIDES 46061 MANDIPROPAMIDE MANDELAMIDE 53624 CYMOXANIL UNCLASSIFIED 42336

MANDIPROPAMIDE MANDELAMIDE 42934 CYMOXANIL UNCLASSIFIED 52359 PROPYZAMIDE AMIDE 40458

METHOMYL CARBAMATES 39985 PROPYZAMIDE AMIDE 45302 HYDROGEN PEROXIDE PEROXIDE 36573

ZETA-CYPERMETHRIN PYRETHROIDS PYRETHRINS

39041 AMETOCTRADIN TRIAZOLOPYRIMIDINE 43820 ETHANEPEROXOIC ACID PEROXIDE 36573

CYMOXANIL UNCLASSIFIED 38111 SPIROTETRAMAT KETOENOLS 40915 ZETA-CYPERMETHRIN PYRETHROIDS PYRETHRINS

33801

FENAMIDONE IMIDAZOLINONES 34963 ZETA-CYPERMETHRIN PYRETHROIDS PYRETHRINS

35862 AMETOCTRADIN TRIAZOLOPYRIMIDINE 33364

SPIROTETRAMAT KETOENOLS 31126 METHOMYL CARBAMATES 31274 SPIROTETRAMAT KETOENOLS 31154

BIFENTHRIN PYRETHROIDS PYRETHRINS

30544 CHLORANTRANILIPROLE DIAMIDES 31102 MANCOZEB DITHIOCARBAMATE, INORGANIC-ZINC

30243

CLETHODIM CYCLOHEXENONE DERIVATIVE

30094 MANCOZEB DITHIOCARBAMATE, INORGANIC-ZINC

30382 CHLORANTRANILIPROLE DIAMIDES 29401

REYNOUTRIA SACHALINENSIS MICROBIAL 29852 BIFENTHRIN PYRETHROIDS PYRETHRINS

29628 FLUPYRADIFURONE NEONICOTINOID 27893

AMETOCTRADIN TRIAZOLOPYRIMIDINE 28866 CLETHODIM CYCLOHEXENONE DERIVATIVE

29098 FENAMIDONE IMIDAZOLINONES 26782

MANCOZEB DITHIOCARBAMATE, INORGANIC-ZINC

26583 IMIDACLOPRID NEONICOTINOIDS 27440 CLETHODIM CYCLOHEXENONE DERIVATIVE

25776

IMIDACLOPRID NEONICOTINOIDS 26534 SULFUR INORGANIC 25351 BIFENTHRIN PYRETHROIDS PYRETHRINS

25135

PHOSPHOROUS ACID INORGANIC 24112 REYNOUTRIA SACHALINENSIS MICROBIAL 24991 METHOMYL CARBAMATES 24777

Table 5 continued

EMAMECTIN BENZOATE

AVERMECTINS, MILBEMYCINS

22331 FAMOXADONE OXAZOLIDINE-DIONES 24246 SULFUR INORGANIC 24745

SULFUR INORGANIC 20336 FLONICAMID FLONICAMID 23759 OXATHIAPIPROLIN UNKNOWN 23701

FLONICAMID FLONICAMID 18649 OXATHIAPIPROLIN UNKNOWN 23462 BENSULIDE ORGANOPHOSPHATES 22486

METALAXYL-M XYLYLALANINE 18231 METALAXYL-M XYLYLALANINE 22299 IMIDACLOPRID NEONICOTINOIDS 20563

BENSULIDE ORGANOPHOSPHATES 17949 PHOSPHOROUS ACID INORGANIC 22199 METHOXYFENOZIDE DIACYLHYDRAZINE 20550

FLUBENDIAMIDE DIAMIDES 17068 BENSULIDE ORGANOPHOSPHATES 21321 FLONICAMID FLONICAMID 19954

METHOXYFENOZIDE DIACYLHYDRAZINE 16657 SPINOSAD SPINOSYN 21125 REYNOUTRIA SACHALINENSIS MICROBIAL 17083

BENFLURALIN 2,6-DINITROANILINE 16537 EMAMECTIN BENZOATE AVERMECTINS, MILBEMYCINS

20555 SULFOXAFLOR SULFOXIMINES 17054

SPINOSAD SPINOSYN 13609 SULFOXAFLOR SULFOXIMINES 19649 FAMOXADONE OXAZOLIDINE-DIONES 16023

THIAMETHOXAM NEONICOTINOIDS 12895 FLUPYRADIFURONE NEONICOTINOID 18939 EMAMECTIN BENZOATE AVERMECTINS, MILBEMYCINS

15395

PENDIMETHALIN 2,6-DINITROANILINE 12718 ACETAMIPRID NEONICOTINOIDS 16982 PHOSPHOROUS ACID INORGANIC 15106

ESFENVALERATE PYRETHROIDS PYRETHRINS

12657 BENFLURALIN 2,6-DINITROANILINE 14010 ACETAMIPRID NEONICOTINOIDS 14369

TOLFENPYRAD PYRAZOLE 12550 PYRACLOSTROBIN STROBIN 13174 METALAXYL-M XYLYLALANINE 14083

INDOXACARB OXADIAZINES 12433 ACIBENZOLAR-S-METHYL UNCLASSIFIED 11444 BENFLURALIN 2,6-DINITROANILINE 13018

ABAMECTIN AVERMECTINS, MILBEMYCINS

12376 THIAMETHOXAM NEONICOTINOIDS 11223 ABAMECTIN AVERMECTINS, MILBEMYCINS

12623

ACIBENZOLAR-S-METHYL UNCLASSIFIED 12312 PYROXSULAM TRIAZOLOPYRIMIDINE 10773 PYROXSULAM TRIAZOLOPYRIMIDINE 12269

PYRACLOSTROBIN STROBIN 10856 ABAMECTIN AVERMECTINS, MILBEMYCINS

10752 SPINOSAD SPINOSYN 11866

FAMOXADONE OXAZOLIDINE-DIONES 10844 INDOXACARB OXADIAZINES 10432 PENTHIOPYRAD SUCCINATE DEHYDROGENASE INHIBITOR

11193

ACETAMIPRID NEONICOTINOIDS 10236 METHOXYFENOZIDE DIACYLHYDRAZINE 9996 PYRACLOSTROBIN STROBIN 11113

MALATHION ORGANOPHOSPHATES 10073 GLYPHOSATE-ISOPROPYLAMMONIUM

PHOSPHONOGLYCINE 9719 GLYPHOSATE-ISOPROPYLAMMONIUM

PHOSPHONOGLYCINE 10895

TRIBENURON-METHYL SULFONYLUREA 9899 PENTHIOPYRAD SUCCINATE DEHYDROGENASE INHIBITOR

9622 DIMETHOATE ORGANOPHOSPHATES 10687

THIFENSULFURON SULFONYLUREA 9899 FOSETYL-AL UNCLASSIFIED 9157 MEPIQUAT CHLORIDE QUATERNARY AMMONIUM COMPOUND

10209

PENTHIOPYRAD SUCCINATE DEHYDROGENASE INHIBITOR

9625 MALATHION ORGANOPHOSPHATES 8343 DIURON UREA 9604

Table 5 continued

GLYPHOSATE-ISOPROPYLAMMONIUM

PHOSPHONOGLYCINE 9531 IPRODIONE DICARBOXIMIDE 7982 THIDIAZURON UREA 9586

CYFLUTHRIN PYRETHROIDS PYRETHRINS

9407 CARFENTRAZONE-ETHYL TRIAZOLONE 7547 PENDIMETHALIN 2,6-DINITROANILINE 9312

BUPROFEZIN BUPROFEZIN 9155 BACILLUS THURINGIENSIS, SUBSP. AIZAWAI STRAIN ABTS 1857

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

7482 ACIBENZOLAR-S-METHYL UNCLASSIFIED 9136

GLYCINE, N-(PHOSPHONOMETHYL)- POTASSIUM SALT

PHOSPHONOGLYCINE 9022 PARAQUAT DICHLORIDE BIPYRIDYLIUM 7435 GLYCINE, N-(PHOSPHONOMETHYL)- POTASSIUM SALT

PHOSPHONOGLYCINE 9122

IPRODIONE DICARBOXIMIDE 8471 MEPIQUAT CHLORIDE QUATERNARY AMMONIUM COMPOUND

7369 MALATHION ORGANOPHOSPHATES 9023

FOSETYL-AL UNCLASSIFIED 6882 THIFENSULFURON SULFONYLUREA 7279 BETA-CYFLUTHRIN PYRETHROIDS PYRETHRINS

8734

PYRAFLUFEN-ETHYL PYRAZOLYLPHENYL 6670 TRIBENURON-METHYL SULFONYLUREA 7279 THIAMETHOXAM NEONICOTINOIDS 7722

MEPIQUAT CHLORIDE QUATERNARY AMMONIUM COMPOUND

6457 FLUXAPYROXAD ANILIDE, PYRAZOLE 7229 ESFENVALERATE PYRETHROIDS PYRETHRINS

7600

FLUXAPYROXAD ANILIDE, PYRAZOLE 6366 GLYCINE, N-(PHOSPHONOMETHYL)- POTASSIUM SALT

PHOSPHONOGLYCINE 7226 PYRAFLUFEN-ETHYL PYRAZOLYLPHENYL 6668

BETA-CYFLUTHRIN PYRETHROIDS PYRETHRINS

6320 PENDIMETHALIN 2,6-DINITROANILINE 6699 PYRETHRINS PYRETHROIDS PYRETHRINS

6342

DIMETHOATE ORGANOPHOSPHATES 6255 TRINEXAPAC-ETHYL UNCLASSIFIED 6179 THIFENSULFURON SULFONYLUREA 6022

PYROXSULAM TRIAZOLOPYRIMIDINE 6052 TRIFLURALIN 2,6-DINITROANILINE 6002 TRIBENURON-METHYL SULFONYLUREA 6022

CLODINAFOP-PROPARGYL ARYLOXYPHENOXY PROPIONIC ACID

5914 ESFENVALERATE PYRETHROIDS PYRETHRINS

5963 INDOXACARB OXADIAZINES 5928

FLUPYRADIFURONE NEONICOTINOID 5850 FLUBENDIAMIDE DIAMIDES 5779 TRIFLURALIN 2,6-DINITROANILINE 5880

TRIFLURALIN 2,6-DINITROANILINE 5621 DIMETHOATE ORGANOPHOSPHATES 5339 QUINOXYFEN QUINOLINE 5790

CARFENTRAZONE-ETHYL TRIAZOLONE 5537 QUINOXYFEN QUINOLINE 5337 PARAQUAT DICHLORIDE BIPYRIDYLIUM 5702

QUINOXYFEN QUINOLINE 4720 PYRIPROXYFEN PYRIPROXYFEN 5157 AZOXYSTROBIN STROBIN 5366

DCPA ALKYL PHTHALATE 4640 CYANTRANILIPROLE DIAMIDES 5034 CYANTRANILIPROLE DIAMIDES 5256

SULFOXAFLOR SULFOXIMINES 4568 TOLFENPYRAD PYRAZOLE 4854 IPRODIONE DICARBOXIMIDE 5199

PARAQUAT DICHLORIDE BIPYRIDYLIUM 4439 FLUOPICOLIDE PYRIDINYL-ETHYL-BENZAMIDES

4835 CARFENTRAZONE-ETHYL TRIAZOLONE 4462

PYRETHRINS PYRETHROIDS PYRETHRINS

4375 DCPA ALKYL PHTHALATE 4795 BOSCALID ANILIDE 4461

DIURON UREA 4355 PYRETHRINS PYRETHROIDS PYRETHRINS

4460 FOSETYL-AL UNCLASSIFIED 4461

Table 5 Continued

THIDIAZURON UREA 4355 BUPROFEZIN BUPROFEZIN 4267 TRIFLUMIZOLE AZOLE 4325

OXATHIAPIPROLIN UNKNOWN 4353 CLODINAFOP-PROPARGYL ARYLOXYPHENOXY PROPIONIC ACID

4152 DCPA ALKYL PHTHALATE 4170

DINOTEFURAN NEONICOTINOIDS 4248 OXYFLUORFEN DIPHENYL ETHER 3904 TRIBUFOS ORGANOPHOSPHATES 4163

S-METOLACHLOR CHLOROACETANILIDE 3810 ACEPHATE ORGANOPHOSPHATES 3841 AZADIRACHTIN BOTANICAL 4149

TRINEXAPAC-ETHYL UNCLASSIFIED 3692 BOSCALID ANILIDE 3769 FLUBENDIAMIDE DIAMIDES 3750

EPTAM THIOCARBAMATE 3584 AZOXYSTROBIN STROBIN 3750 OXYFLUORFEN DIPHENYL ETHER 3592

OXYFLUORFEN DIPHENYL ETHER 3437 TRIFLUMIZOLE AZOLE 3652 FLUXAPYROXAD ANILIDE, PYRAZOLE 3401

ACEPHATE ORGANOPHOSPHATES 3324 S-METOLACHLOR CHLOROACETANILIDE 3424 CLODINAFOP-PROPARGYL ARYLOXYPHENOXY PROPIONIC ACID

3368

IMAZAMOX IMIDAZOLINONE 3293 DIURON UREA 3292 CYFLUTHRIN PYRETHROIDS PYRETHRINS

3190

CYANTRANILIPROLE DIAMIDES 3004 THIDIAZURON UREA 3292 BACILLUS THURINGIENSIS, SUBSP. AIZAWAI STRAIN ABTS 1857

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

3117

PYRIPROXYFEN PYRIPROXYFEN 2965 CYFLUFENAMID AMIDE 3154 S-METOLACHLOR CHLOROACETANILIDE 2971

AZOXYSTROBIN STROBIN 2856 EPTAM THIOCARBAMATE 3063 MEPIQUAT PENTABORATE QUATERNARY 2914

BACILLUS THURINGIENSIS, SUBSP. AIZAWAI STRAIN ABTS 1857

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

2573 BETA-CYFLUTHRIN PYRETHROIDS PYRETHRINS

3043 PYRIPROXYFEN PYRIPROXYFEN 2836

AZADIRACHTIN BOTANICAL 2522 CHLORPYRIFOS ORGANOPHOSPHATES 2923 CYFLUFENAMID AMIDE 2711

FLUOPICOLIDE PYRIDINYL-ETHYL-BENZAMIDES

2318 CYAZOFAMID AZOLE 2911 ACEPHATE ORGANOPHOSPHATES 2689

BOSCALID ANILIDE 2255 PYRAFLUFEN-ETHYL PYRAZOLYLPHENYL 2816 ETOXAZOLE ETOXAZOLE 2589

DIMETHYLAMINE 4-(2,4-DICHLOROPHENOXY)BUTYRATE

PHENOXY-CARBOXYLIC-ACID

2254 AZADIRACHTIN BOTANICAL 2754 IMAZAMOX IMIDAZOLINONE 2513

CYTOKININ BOTANICAL 2248 CYFLUTHRIN PYRETHROIDS PYRETHRINS

2727 CYTOKININ BOTANICAL 2477

CYAZOFAMID AZOLE 2185 DINOTEFURAN NEONICOTINOIDS 2388 SPIROMESIFEN KETOENOLS 2465

CHLORPYRIFOS ORGANOPHOSPHATES 2166 IMAZAMOX IMIDAZOLINONE 2350 IMAZETHAPYR, AMMONIUM SALT

IMIDAZOLINONE 2413

IMAZETHAPYR, AMMONIUM SALT

IMIDAZOLINONE 2095 BACILLUS THURINGIENSIS SUBSP. KURSTAKI, STRAIN ABTS-351,FERMENTAION SOLIDS, SPORES, AND INSECTICIDAL TOXINS

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

2215 EPTAM THIOCARBAMATE 2274

TRIFLUMIZOLE AZOLE 2049 PROPICONAZOLE AZOLE 2183 TOLFENPYRAD PYRAZOLE 2146

TRIBUFOS ORGANOPHOSPHATES 1952 METCONAZOLE AZOLE 1997 DINOTEFURAN NEONICOTINOIDS 2110

Table x5continued

DIAZINON ORGANOPHOSPHATES 1936 MEPIQUAT PENTABORATE QUATERNARY 1935 CHLORPYRIFOS ORGANOPHOSPHATES 2103

BACILLUS THURINGIENSIS SUBSP. KURSTAKI, STRAIN ABTS-351,FERMENTAION SOLIDS, SPORES, AND INSECTICIDAL TOXINS

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

1831 METAM-SODIUM DITHIOCARBAMATE 1840 ETHEPHON ORGANOPHOSPHATES 1856

DICAMBA, DIGLYCOLAMINE SALT

BENZOIC ACID 1686 CYTOKININ BOTANICAL 1781 DICAMBA, DIGLYCOLAMINE SALT

BENZOIC ACID 1822

NALED ORGANOPHOSPHATES 1626 POTASSIUM 1-NAPHTHALENEACETATE

NAPHTHALENE ACETIC ACID DERIVATIVE

1740 CRYOLITE INORGANIC 1750

CYFLUFENAMID AMIDE 1548 OCTANOIC ACID, COPPER SALT INORGANIC-COPPER 1709 OCTANOIC ACID, COPPER SALT INORGANIC-COPPER 1726

METCONAZOLE AZOLE 1511 NALED ORGANOPHOSPHATES 1656 MYCLOBUTANIL AZOLE 1708

GLUFOSINATE PHOSPHONOGLYCINE 1499 BACILLUS THURINGIENSIS SUBSP. AIZAWAI STRAIN GC-91

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

1621 BUPROFEZIN BUPROFEZIN 1674

MEPIQUAT PENTABORATE QUATERNARY 1475 (Z)-11-HEXADECENYL ACETATE PHEROMONE 1543 HEXYTHIAZOX UNCLASSIFIED 1548

BROMOXYNIL HEPTANOATE HYDROXYBENZONITRILE 1425 MCPA, DIMETHYLAMINE SALT CHLOROPHENOXY ACID OR ESTER

1520 POTASSIUM 1-NAPHTHALENEACETATE

NAPHTHALENE ACETIC ACID DERIVATIVE

1405

BROMOXYNIL OCTANOATE HYDROXYBENZONITRILE 1425 TRIBUFOS ORGANOPHOSPHATES 1507 COPPER HYDROXIDE INORGANIC-COPPER 1385

CLARIFIED HYDROPHOBIC NEEM OIL

BOTANICAL 1282 SPIROMESIFEN KETOENOLS 1320 QST 713 STRAIN OF BACILLUS SUBTILIS

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

1375

PROPICONAZOLE AZOLE 1255 QST 713 STRAIN OF BACILLUS SUBTILIS

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

1269 PHORATE ORGANOPHOSPHATES 1297

CYCLOATE THIOCARBAMATE 1219 (Z)-11-HEXADECENAL PHEROMONE 1216 PROMETRYN TRIAZINE 1265

MCPA, DIMETHYLAMINE SALT CHLOROPHENOXY ACID OR ESTER

1205 BACILLUS AMYLOLIQUEFACIENS STRAIN D747

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

1184 TRINEXAPAC-ETHYL UNCLASSIFIED 1199

HEAT-KILLED BURKHOLDERIA SP STRAIN A396 CELLS AND SPENT FERMENTATION MEDIA

MICROBIAL 1107 PROMETRYN TRIAZINE 1150 METAM-SODIUM DITHIOCARBAMATE 1156

PROMETRYN TRIAZINE 1060 GLUFOSINATE PHOSPHONOGLYCINE 1001 PROPICONAZOLE AZOLE 1099

OCTANOIC ACID, COPPER SALT INORGANIC-COPPER 1032 NOVALURON BENZOYLUREAS 919 CYAZOFAMID AZOLE 1071

ETOXAZOLE ETOXAZOLE 999 FLUDIOXONIL PYRROLE 900 HEAT-KILLED BURKHOLDERIA SP STRAIN A396 CELLS AND SPENT FERMENTATION MEDIA

MICROBIAL 1032

BACILLUS AMYLOLIQUEFACIENS STRAIN D747

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

983 DICAMBA, DIGLYCOLAMINE SALT

BENZOIC ACID 862 METCONAZOLE AZOLE 1000

Table 5 continued

POTASSIUM 1-NAPHTHALENEACETATE

NAPHTHALENE ACETIC ACID DERIVATIVE

959 CRYOLITE INORGANIC 862 (Z)-11-HEXADECENYL ACETATE PHEROMONE 1000

METAM-SODIUM DITHIOCARBAMATE 893 ETOXAZOLE ETOXAZOLE 856 (Z)-11-HEXADECENAL PHEROMONE 968

CHLOROTHALONIL SUBSTITUTED BENZENE 849 DIMETHYLAMINE 4-(2,4-DICHLOROPHENOXY)BUTYRATE

PHENOXY-CARBOXYLIC-ACID

799 FLUOPICOLIDE PYRIDINYL-ETHYL-BENZAMIDES

886

QST 713 STRAIN OF BACILLUS SUBTILIS

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

748 IMAZETHAPYR, AMMONIUM SALT

IMIDAZOLINONE 772 BACILLUS PUMILUS STRAIN QST 2808

MICROBIAL 884

COPPER HYDROXIDE INORGANIC-COPPER 738 CHLOROTHALONIL SUBSTITUTED BENZENE 723 BACILLUS THURINGIENSIS SUBSP. KURSTAKI, STRAIN ABTS-351,FERMENTAION SOLIDS, SPORES, AND INSECTICIDAL TOXINS

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

865

DICLORAN SUBSTITUTED BENZENE 737 PHORATE ORGANOPHOSPHATES 717 CHLOROTHALONIL SUBSTITUTED BENZENE 824

BACILLUS THURINGIENSIS SUBSP. AIZAWAI STRAIN GC-91

BACILLUS SUBTILIS AND THE FUNGICIDAL LIPOPEPTIDES

725 CYCLOATE THIOCARBAMATE 714 TEBUCONAZOLE AZOLE 759

PHORATE ORGANOPHOSPHATES 699 SETHOXYDIM CYCLOHEXENONE DERIVATIVE

659 SETHOXYDIM CYCLOHEXENONE DERIVATIVE

700

ASPERGILLUS FLAVUS STRAIN AF36

MICROBIAL 698 FENOXAPROP-P-ETHYL ARYLOXYPHENOXY PROPIONIC ACID

655 FLUDIOXONIL P