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75 -cow dairy herd will generate more than 6,800 Ibof PlOS and 16,700 Ib of N annually. The cowsdeposit this fertilizer in holding areas, along walk-ing lanes and in pastures. Understanding thecycling and flow of nutrients will help maximize thefertilizer or manure nutrients in your grazing sys-tem. It also will help you identify when and whereyou need to purchase additional fertilizer toimprove the productivity of your crops.

Nutrients enter the fann in purchased fertilizer,as part of purchased feeds and mineral supplements,and through natural processes such as nitrogen fixa-tion by legumes. Nutrients leave the farm in the milkand crops and through natural processes such asammonia volatilization and in runoff. On conven-tional dairies that rely on purchased hay, concentratesand mineral supplements, more nutrients enter thefann in feed than are exported from the farm as milk.

In a grazing system, most nutrients in themanure end up on the pastures. Nutrients fed in themilking parlor are transported to the pasture by theanimals. In a grazing dairy, at least 65 percent of thenutrients in the concentrate are excreted on the pas-ture. The amount of nutrients returned to the pas-ture depends on the time the cows spend in theholding pen and dairy parlor. Most nutrients in theforage from pastures are recycled back. Hay balesbrought into paddocks as supplemental forage carrynutrients. The average 1,000-lb bale contains 20 Ibof N, 61b of PlOS and 251b ofK2O, most of whichwill be deposited on the field where it is consumed.

The flow of nutrients in a pasture system is dif-ferent from that of hay or row crop fields. Most ofthe nutrients in the aboveground biomass are har-vested and removed from hay and row crop fields.For example, 80 percent of the nutrients in stand-ing hay are removed with the bales. The highremoval rates of N, P and K from these fields mayrequire equally large nutrient inputs to maintainsoil fertility over long periods of time.

Plant persistence and productivity oftendepend on sources of nitrogen (N), phosphorus (P)and potassium (K) in excess of what the soil canprovide. Pasture systems have lower fertilizer needsthan hay and row crops because many of the nutri-ents consumed by the animals are returned to thepasture in the manure. In addition to recycling thenutrients in the forage, animals import nutrientsinto the pasture from purchased feeds. Phosphoruslevels in a pasture-based dairy can increase withoutthe addition of fertilizer because of nutrient contri-butions from purchased hay and concentrates.

Successful pasture management uses soil testing,an understanding of nutrient cycles, and the judi-cious use of lime and fertilizers to maxiInize the per-sistence of desirable pasture species and improvepasture productivity. This typically requires a depar-ture from the fertilization strategies used in row cropsystems. Management-intensive grazing (MiG)improves the recycling of nutrients within a pastureby better distributing nutrients from nutrientsaround the pasture. This minimizes, but does noteliminate, the need for fertilizer applications.

Much of Missouri's dairy production is in theOzarks, a region known for clear-water streams andlakes. Surface waters in this region of the state areparticularly sensitive to nutrient losses from agricul-tural practices. Pastures are among the most envi-ronmentally benign agricultural systems. However,significant nutrient losses can occur from pastures,particularly in winter feeding areas, from animalactivity near stream banks and after the applicationof fertilizer. Maintaining riparian zones along thelakes and streams and carefully managing winterfeeding areas can minimize these losses.

Nutrient flow and cycling in dairy systems

Lactating cows excrete in urine and feces morethan 70 percent of the N, 60 percent of the p and80 percent of the K they consume in their diets. A

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Table 10.1. Estimated removal of N, p and K from a field under different management systems.

Note: To adjust values to a per acre basis, multiply hay values by the yield per acre in tons and divide the animal numbers by theannual stocking rate in acres per animal. Adjust P to P20S basis by dividing by 0.44. Adjust K to K20 basis by dividing by 0.83.

The philosophy of our current fertilization sys-tem was developed in these demanding systems.We recommend regular applications of P and Kfertilizers unless soil test levels are very high. Andwe recommend annual applications of N fertilizersunless sufficient legumes are in the field to meet theN deficit through nitrogen fixation.

In pasture systems, the flow of nutrients fromthe field is either greatly reduced or in some caseswill be less than what is exported (I'able 10.1).Animal behavior and manure characteristics con-trol the distribution and availability of most nutri-ents. Pasture-based systems require different soiltesting and fertilizer management than row crops.

A nutrient cycle describes the flow of nutrientsin, out and within a pasture. Figure 10.1 outlines thekey nutrient-flow pathways for P, K and N.Nutrient pools in the pasture include the soil pools(plant-available nutrients and soil storage), plants,animals and the atmosphere. Note that each nutri-ent cycle has unique aspects. The greatest differ-ences are between the N cycle and the P and Kcycles. For example, the N cycle includes loss path-ways to the atmosphere that do not exist in the Pand K cycles.

Our objective in soil fertility management is tomaintain the plant-available soil pool of nutrients ata sufficient level to support quality forage produc-tion for animals while protecting water quality.Exports from the pasture deplete the plant-avail-able nutrient pool in the soil by transporting nutri-ents out of the pasture instead of recycling themback into the soil pool.

Harvested crops are the primary mechanism forP and K losses from the field. Phosphorus andpotassium also can be lost in runoff water passingover the field. These losses are not large enough toaffect fertilizer management. For example, phos-phorus losses from pasture are typically less than 1lb P/acre from well-managed pastureland.

There will be litde change or even an increasein soil test P and K values over time in a pasture ifmanure is well-distributed in a field. The animalsare either removing few nutrients from the system,or they are adding nutrients (rable 10.1 ). There arefew uncontrolled losses to water and air.Consequently, annual applications of P and K arenot needed to maintain soil fertility levels in well-managed pastures. Instead, soil test paddocks every3 to 5 years and apply fertilizer when soil test levelsdrop below desired levels.

In contrast, the N cycle has uncontrolled lossesthat can exceed exports in hay, meat or milk. Themost important loss pathway in pastures is ammo-nia volatilization. On average, 25 percent of thenitrogen in the urine and feces deposited in a fieldis lost as ammonia to the atmosphere, but losses canapproach 50 percent under some conditions. A typ-ical dairy cow excretes 220 to 260 Ib of N annually,but up to half (110 to 130 Ib) is lost to the atmos-phere through ammonia volatilization. Some of theorganic N in manure is unavailable to plants, whichfurther reduces the value of manure N returned tothe pasture. Plants in the pasture ultimately recover10 percent of the N in the feces and 30 percent ofthe N in urine. Consequently, the annual N fertil-izer value of dairy manure excreted in the field is130 to 155 Ib/cow.

Annual inputs of N are recommended for pas-ture systems. Dairies that feed high amounts ofconcentrates will need to apply lower rates of N,and dairies that depend more on forages will needto apply higher rates of N to the pastures. Thesource of N can be purchased fertilizer, manurefrom a manure-storage facility or fixed N fromlegumes in the forage mix. Maintaining a vigorouslegume component of at least 30 percent of the for-age stand all but eliminates a response to fertilizerN in pasture systems.

In summary, pasture systems are more efficient

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Phosphorus(P)

Potassium (K)

Nitrogen (N)

Figure 10.1. Key aspects of the phosphorus (P), potassium (K) and nitrogen (N) cycles.

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than other agricultural systems, such as hay androw crops, at recycling most nutrients. Nitrogen isthe exception to this rule; an N source is needed toreplace the N where it is removed by the animals,lost in uncontrollable ways such as ammoniavolatilization or in a field with reduced availabilityof organic N .

and shade carrying forage nutrients in their gut. Inthe loafing areas they rest, rise, defecate and thenreturn to the D1ain grazing area ready to harvestand reD1ove another load of forage nutrients.

As grazing intensity increases, the tiD1erequired to ensure coD1plete coverage of the pas-ture with D1anure decreases (Table 10.2). ID1provednutrient distribution is a tangible benefit of adopt-ing a D1ore intensive grazing strategy.

Table 10.2. The effect of grazing intensity on manure distribu-tion in pastures.

Making fertilizer decisionsin pasture systems

Manure distribution in pastures

Feces and urine from grazing animals are a crit-ical source of nutrients in pasture. In pasture sys-tems, cows are fertilizer spreaders mat control medistribution of mese needed nutrients. A dairy cowdefecates 7 to 15 times per day and urinates 8 to 12times per day. Each time a cow urinates, it appliesnitrogen at me rate of 500 to 1,000 lb N/acre andwater at me rate of lOO inches/hour to a small por-tion of me field. Each time a cow defecates, itapplies nitrogen at me rate of 200 to 700 lb N/acre.

These nutrients are of little use as a fertilizerunless mey are well-distributed across me surfaceof a pasture. Grazing animals typically cover up to20 percent of me pasture annually wim urine andmanure patches. These patches may not be uni-formly distributed over me field.

As a general rule, me heavier me grazing pres-sure, me more uniformly manure and urine nutri-ents will be distributed across me pasture. Researchat me Forage Systems Research Center determinedme distribution of manure piles in a 3-, 12- and 24-paddock grazing system. In me 3-paddock system,manure piles (and nutrients) were concentratedwithin 150 feet of water and shade. Soil test p lev-els dramatically increased in mese two areas, butmey decreased or stayed constant in me main graz-ing areas. In me 24-paddock system, mere was stillsome concentration of manure piles near water, butme main grazing area had 2 to 4 times me densityof manure piles as me 3-paddock system.

This research was used to estimate how long itwould take to have a manure pile land in everysquare yard of a pasture (Table 10.2). A continu-ously grazed pasture requires an estimated 27 yearsto ensure every square yard of me paddock hasreceived at least one manure pile while omer areasrepeatedly receive manure. Meanwhile parts of mepasture are unfertilized wim manure for 27 years.

The main grazing area in a continuously grazedpasture has a nutrient cycle more like a hay fieldman a pasture. Cows graze in me main paddockarea and men move to me loafing areas near water

Soil sampling pastures

Soil sampling is an important tool for under-standing the opportunities and limitations of a pas-ture for forage production. Soil fertility levels inpastures are highly variable, which makes accuratesoil sampling difficult. A few general rules will helpimprove the quality of your soil test results.

A soil sample should represent a maximum of20 acres and preferably much less. Divide fieldsbased on topography, previous management and/orsoil type. It often makes sense to sample each pad-dock in a grazing system separately, particularly ifpaddocks have had different fertilization historiesor different management histories such as onebeing hayed and the other not.

.Avoid sampling within 150 feet of wateringpoints, shade trees and other loafing areas.These areas typically have sufficient fertility,and their inclusion will overestimate nutrientlevels in the main pasture areas.

.Sample the soil with a coring device, combininga minimum of 15 to 20 cores into a plasticbucket. Travel through the sampling area in azigzag pattern collecting a core at regular inter-vals at random points in the field. After youhave collected the cores from a sampling area,crumble and thoroughly mix the soil in yourbucket and then remove a subsample to send infor analysis. Discard the excess soil.

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tence of many forage species. While medium-test-ing soils may respond to fertilizer, the responsewill be smaller than for low- or very low-testingsoils. In some fields, no benefit will be observed toadding fertilizer. The application of fertilizer tosoils that test high will not increase forage produc-tion. In row crop fields and continuously grazedpastures, maintenance applications of phosphorusand potassium are recommended. N o fertilizer isrecommended for agronomic purposes on soilstesting very high or excessive.

Maintenance applications of phosphorus andpotassium are not needed in intensively grazed pas-tures that return high amounts of nutrients back tothe field through urine and feces. For intensivelymanaged pastures, monitor soil test levels with soiltesting. Apply fertilizer when you need to raise soiltest levels to a more desirable level.

.In continuously grazed pastures, avoid takingcores through manure piles and fresh urinepatches. In pastures with high grazing densities,avoid the freshest manure piles.

.The lab where you send your samples deter-mines sampling depth. Sending 3-inch samplesto a lab expecting 6-inch samples or vice versawill result in inaccurate soil test results. TheMissouri soil testing laboratory requires a 6-inch sampling depth-

.Send your soil samples to a qualified soil testlaboratory that is accredited by the NorthAmerican Proficiency Testing program as wellas by your own state's accreditation program. Besure to clearly label samples so you can identifywhich field is associated with each soil sample-

.In most cases, the lab will provide recommen-dations for N, P, K and lime based on soil testresults, which you should receive within oneweek of submitting your soil samples-

.Sample your pastures' soil every 3 to 5 years. It isbetter to do a careful job of soil sampling every 5years than a sloppy job every 3 years or less.

Should I fertilize my pasture?

Before you can answer this question, you needto collect some information and answer some otherquestions. Critical information to address thisquestion includes:

.What forage(s) do you want to grow?

.What are your soil test levels?

.What are other potential limitations to pastureproductivity on that pasture?

.What is the value of your forage?

Interpreting soil test results

Soil testing provides infonnation about thenutrient status of the soil needed to effectivelymanage pastures. The pH of the soil and the avail-ability of nutrients provide critical infonnationabout the potential productivity of the pasture andthe species likely to compete effectively.

Soils that test low for a particular nutrient arelikely to increase yield if that fertilizer is added.Low- and very low-testing soils reduce the persis-

Answering these questions will allow you todetermine your options.

Forage selection is a key part of any fertilitydecision. Forages differ in the minimum fertility

Table 10.3. Range of soil test levels of pH, K and p required for persistence of selected forages.

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of forages such as alfalfa that have high establish-ment costs.

Fertilizer and lime is most likely to pay on low-testing soils. The biggest benefits in yieldresponse, persistence and forage quality occur onvery low and low-testing soils. With limitedresources, focus your lime, p and K fertilizer pro-grams on these low-testing soils and/or on main-taining your high-value forages such as alfalfa.Low rates of p and K on all low-testing soils ismore likely to pay than higher rates on a subset oflow-testing soils.

level needed for persistence and productivity (Table10.3). In general, legumes require higher pH, p andK levels than most grass species. If you havemedium to high soil test levels of pH, p and K, youwill have few restrictions on your selection of for-age and little need to build up p and K or raise pH.If soil test levels are low, you will need to apply fer-tilizer and lime if you want to maintain legumes inyour pasture. Low-testing soils also reduce thequality and quantity of grass forages.

Forages have high value in dairy systems,which makes fertilization profitable. The follow-ing practices maximize returns on fertilizer in pas-ture systems.

.Maximize forage use. The animals in typicalMissouri pastures use less than 50 percent ofthe forage. Intensive management can increasethis to more than 75 percent.

.Apply N fertilizer only when you expect a yieldresponse and when you can use the extra forageproduction.

.As milk prices rise, fertilization of pasture andhay becomes more profitable.

Fertilizing a mixed grass/legume pastureAdding legumes to a grass pasture can improve

pasture yield, increase animal gains and providesome N for the grass. But fertilizing a mixed swardis difficult. The thing to remember is this: Mostlegumes will not grow or persist well if soil fertilityis low. This is especially true for alfalfa and redclover. The basic fertilizer strategy for keepinglegumes in a pasture is:

1. Keep the soil pH between 6.0 and 7.5 withapplication of lime.

2. Maintain soil phosphorus and potassium in themedium to high range.

3. Avoid fertilizing mixed grass/legume pastureswith nitrogen.

Remember that all pastures need annual inputsof N to maintain productivity. The N source can befrom manure, fertilizer and/or nitrogen fixation bylegumes. If soil test levels are too low to maintain alarge legume component, annual applications offertilizer N will be needed. Legumes must be atleast 30 percent of the stand to eliminate responseto commercial nitrogen fertilizer.

Nitrogen fertilization can happen in manyforms. Investing in legume seed for interseeding isa form of N fertilization. Purchasing manure froma neighbor provides N for the crop. Investment infencing to improve manure distribution is a form offertilization for parts of the pasture. Purchased fer-tilizer is another alternative.

Only invest in fertilizer when you have a needfor additional forage or higher-quality forage andthere is a potential for fertilizer response. Summerand fall N fertilization can increase yield whenthere is a lack of forage while the same fertilizerapplied in spring may grow excess forage with littlevalue. If you don't need the forage, don't fertilize.

But remember that yield is not the only indica-tor of forage value. Fertilization will increase thenutrient quality of the forage and the persistenceof desirable species. Phosphorus and potassiumwill pay for themselves by extending the stand life

Phosphorus is particularly important in seedlingestablishment, and a "pop-up" application of 20 to40 lb P20s/acre should be applied at seeding toenhance seedling root development and growth.Potassium is particularly important to legume vigor,disease resistance and winter hardiness. Take care toreplace K removed through harvest of excess forageas hay or silage.

Avoid applying fertilizer N to mixed legume/grass swards. Application of N to mixed swards willfavor the grass over the legume. Added fertilizer Nis unlikely to increase yields when 30 percent ormore of the total biomass in a pasture is composedof legumes.

A pure stand of clover can provide more than200 lb N/acre per year through N fixation. Inmixed swards, legumes benefit grasses by transfer-ring N from the legumes to grasses. Very little Nis transferred from living legumes directly tograsses. Grasses primarily benefit from N fixed bylegumes through turnover of the N when thelegumes decompose. This includes decomposition

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of unused forage tissues, decay of old roots andexcreta return of N from legumes ingested by live-stock. This means that the productivity of themixed pasture should improve with time as a nat-ural recycling process is established.

the pasture. To maximize the nutrient benefit ofhay feeding, producers must take care to regularlymove feeding areas around pastures so that sod-trampling damage is reduced and returned nutri-ents are evenly distributed.

Remember that unless you feed hay on the samearea where it was harvested, nutrients from one areaof the farm are being mined while nutrients arebeing added where hay is fed. Hay fields will need tobe fertilized to make up for this difference.

Using nitrogen to encourage faIl versus

spring growth of cool-season grasses

Applying nitrogen fertilizer will usually stimu-late vegetative growth of cool-season grasses.Typically, grass growth will be greatest for 4 to 8weeks immediately following an N fertilizer appli-cation. But applying N fertilizer at the wrong timeof year creates more problems than it solves.

For years, many forage producers have applied60 or more lb N/acre to grass pastures in earlyMarch. This amount of N fertilizer typicallyincreases the supply of forage in spring by 20 to 60percent. However, many farmers are not short offeed in the spring. In fact, most have excess feedduring this period. Applying N fertilizer in thespring does not make much sense if you are alreadydealing with an oversupply of forage.

By far the most economical use of N fertilizer isto enhance fall growth for stockpiling. Almost alllivestock producers are short of pasture during latefall and winter. Most are forced to feed hay to carrystock through the winter. Stockpiling can reducethese costs. Stockpiling takes advantage of the fallgrowth ofcool-season grasses by applying N fertil-izer in late summer and allowing growth to accu-mulate until a killing frost. Then the cows cangraze the forage in the winter. The best way tostimulate stockpile growth is to remove accumu-lated summer growth in late July and then apply 40to 60 lb N/acre in August. It is best to apply the Nearly in August to maximize the growth periodprior to a killing frost.

Purchasing manure as a pasture fertilizerManure can be an excellent inexpensive source

of nutrients for pasture. Poultry litter and soliddairy manure can rapidly build up soil test P and Kvalues on pastures. To maximize the value of thisfertilizer source:

.Ask for the results of a manure analysis for themanure to be applied to a pasture-

.Assume P and K in the manure are equallyavailable as with other fertilizer sources. Beaware that manure test results are sometimesreported as P and K while fertilizer require-ment is reported as phosphate and potash. Toconvert: phosphate (P2OS) = P/0.44, and potash(KzO) = K/0.83.

.Contact your local University Outreach andExtension center or NRCS office for help incalculating the N availability of nitrogen in yourmanure source. All the N in the manure will notbe available. Nitrogen in surface-appliedmanure may be only 60-percent available-

.Be sure manure is uniformly applied.

August is an excellent time to apply manure topasture. The nutrients at that time promote fallgrowth while the potential for nutrient loss inrunoff is low.

Managing pasturesto improve water qualityManaging hay feeding

to maximize nutrient return

Winter hay feeding can be a source of "fertil-izer" if fed properly on pasture. A 1,000-lb bale ofhay contains approximately 6 lb P205 and 25 lb&0. If this is valued at 22 cents/1b P205 and 14cents/1b &0, the fertilizer value of hay fed on pas-ture is approximately $4lbale. Because animalsexcrete more than 60 percent of the P and K theyconsume in hay, these nutrients will be returned to

Surface water qualityNitrogen, phosphorus and potassium are

required for growth by all animals and plants. Lackof these essential nutrients can restrict growth.Fertilizers containing nitrogen, phosphorus andpotassium are applied to crops and forages toincrease yield.

Similarly, nutrient levels in surface water oftenrestrict the growth of aquatic plant and animal life.

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In freshwater lakes and streams, phosphorus is typ-ically the nutrient that most limits growth.Increasing the nutrients, particularly phosphorusand nitrogen, that are entering a stream or lake willincrease the growth of aquatic plants and organ-isms. Although these nutrients are necessary, exces-sive levels overstimulate the lake or stream, whichreduces the quality of the water. The progressivedeterioration of water quality from overstimulationby nutrients is called eutrophication.

As nutrient concentrations increase, the processof eutrophication leads to a predictable reductionin water quality. Initially, increased nutrients willstimulate algae growth, which will reduce waterclarity. Continued degradation of water by excessnutrients will reduce oxygen levels in the water,alter fisheries, lead to fish kills and reduce drinkingwater quality.

The majority of Missouri's dairies are located inthe Ozark region of Missouri. The Ozarks areknown for their clear streams and lakes. These clear-water lakes and streams are the most sensitive toincreased nutrient concentrations. Small increases inphosphorus concentrations in these water bodies willdramatically reduce water clarity, which is a strongindicator of water quality for the general public.Increases in nutrient loads will impair water qualityin other parts of the state, but changes will be lessdramatic in these murkier waters.

Once a lake has excess phosphorus, it takestime to improve water quality. Excess phosphoruscycles between the bottom sediments and thewater long after the phosphorus source has beeneliminated. Consequently, water quality effortsmust focus on prevention.

Managing pastures to maintain

and improve water quality

Agriculture contributes to surface water qualityproblems through the nutrients carried in the runofffrom fields. As runoff water passes over the soil sur-face, it picks up nutrients and soil particles and car-ries them into lakes and streams. This process isclassified as nonpoint source pollution because it isdelivered in the runoff from all the water reachingthe stream from a watershed instead of being con-centrated at one point, which would be the case witha discharge pipe from a sewage treatment plant.Nonpoint pollution from agriculture is now consid-ered one of the leading causes of water pollution by

the u.s. Environmental Protection Agency.Pasture systems can be among the most benign

agricultural systems in their impact on water qual-ity. Well-managed pastures reduce the quantity ofrunoff from a field and the nutrient concentrationin the water compared to row crop ground. Ahealthy stand of forage provides year-round protec-tion from soil erosion; soil particles carry largeamounts of nutrients to the soil. Forage systemspromote water infiltration into the soil, whichreduces the quantity of runoff and thus reduces theload of nutrient reaching the stream or lake. Theextensive network of roots combined with a longgrowing season traps nutrients in the soil, whichreduces the potential for leaching of nutrientsthrough the soil.

However, mismanagement of pasture systemscan result in high losses of nutrients and soil tolakes and streams. Overgrazing and poor-qualitypastures can promote erosion and runoff.Particularly damaging is overgrazing near thebanks of streams and lakes. Runoff from feedingareas and other areas where animals congregate cancarry high nutrient concentrations. An excessivebuildup of nutrients in pastures will increase theconcentration of nutrients in runoff. Manureapplied to cold and frozen soils can support highnutrient concentrations in runoff; animals in pas-ture systems often are depositing nutrients on pas-tures through winter. The site of a defecation orurination event represents a dramatic overapplica-tion of nutrients in a small, localized area. Finally,many of our pasture systems are located on mar-ginal agricultural land prone to erosion and higherrates of runoff.

The losses of nutrients from pastures are smallcompared to the quantities of fertilizer added tothese systems. For example, phosphorus lossesoften are less than 1 lb/acre, an agronomicallyinsignificant rate. However, these losses from manyfields in a watershed combine to create a significantload to a downstream water body. Therefore, lossesthat have no agronomic importance can have a neg-ative impact on water quality.

Stewards of pasture systems have many tools tominimize nutrient losses from their fields. Theymust effectively use these tools to successfully rnin-imize the effect of grazing on water quality. Theobjective of this section is to highlight managementpractices that reduce potential losses from pasturesto streams.

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grazing and by damaging stream banks with hooftraffic. Damage to this zone is particularly detri-mental because it eliminates the protective zonefrom the edge of the stream and because elevatedlosses from the riparian zone are moved direcdyinto the stream or lake.

Protect riparian zones by carefully managinggrazing along stream and lake edges. Short, inten-sive grazing periods with sufficient recovery peri-ods maintain strong forage communities alongstream banks. Fencing animals out of streams is theultimate method of protecting riparian zones.

Animals will inevitably damage stream bankswhen accessing drinking water in streams and lakes.Alternative water sources or construction of con-trolled entry and access points to streams and lakeswill minimize damage on the banks.

One symbol of the negative impact of agricul-ture on water quality is the image of catde defecat-ing direcdy into a stream or lake. Total phosphoruscontent deposited by the cow is approximately 0.01lb per defecation. Studies of simulated rainfallevents estimate runoff from forage systems can con-tain 0.01 to 0.33 lb P in a single rainfall event. Thephosphorus added to the water when a cow defe-cates direcdy into the water can be equivalent to theP load from 1 acre of land in one runoff event.

Prevent erosion and reduce runoff

The primary benefit of pasture systems is theymaintain an actively growing ground cover throughmost of the year. Continuous ground cover of theforage combined with the high root density in thesod acts to protect the soil from erosion.

The leaves protect the soil from the impact ofraindrops, which can dislodge soil particles. Thedense plant community also slows the movement ofrunoff water over the surface of the soil, whichreduces its erosive power and increases the opportu-nity for infiltration. The roots protect the soil fromthe erosive forces of water passing over the surface.The roots and lack of tillage promote a highlydeveloped soil structure that promotes infiltration.

~anagement practices that damage a foragestand will promote greater losses through greaterrunoff volume, greater energy in the runoff andgreater erosion. These practices include:

1. Overgrazing: Overgrazing reduces stand vigorand plant persistence, which causes thinnerstands and less ground cover.

2. Poor soil fertility management: Soils with lowpH or nutrient levels have lower persistenceand vigor of forages, which leads to reducedground cover. Low-fertility pastures are easierto overgraze.

3. Excessive traffic, particularly on saturatedsoils: Hoof action of animals will damageplants and pulverize soil structure on saturatedsoils. This will thin ground cover and reduceinfiltration.

Protect water quality by maintaining swardhealth. To maximize the protective properties ofthe forage stand, maintain a well-balanced soil fer-tility program combined with the correct rotationof pastures to minimize overgrazing and allow suf-ficient regrowth periods.

Proted riparian zones along

the edges of lakes and streams

Manage winter feeding areasWinter feeding areas concentrate nutrients and

animal activity in a limited area; this increases thepotential for nutrient losses to lakes and streams.Nutrients from imported hay and concentrates fedin the milking parlor are deposited in the limitedarea used by the animals in winter. Soils in winteroften are wet or saturated, so animal activity oftendamages the stand and soil structure. Soils also arefrozen or cold, which promotes runoff and slowsthe incorporation of added nutrients into forms lessavailable for loss in runoff. Late fall and/or earlyspring are the periods of the year runoff is mostlikely to occur. Consequently, winter feeding areascreate the potential for high concentrations ofnutrients in runoff during times when runoff islikely to occur.

Winter feeding should only be done on pas-tures where runoff potential is low. Move the place-ment of bales around the pasture to spread nutri-ents around the field and minimize animal traffic inany specific area. Consider developing a confinedarea designed specifically for winter feeding. The

Riparian zones are vegetative areas immediatelyadjacent to the edge of a lake or stream. This 15- to60-foot wide buffer zone plays an important role inprotecting water quality. Plant cover in this zonestabilizes stream banks and filters water, whichreduces the quantity of soil particulates that enterthe stream or lake.

Animals can damage riparian zones by over-

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area can be designed to carry animal traffic in win-ter and collect and store manure until it can beapplied at a more appropriate time of the year.

These areas are likely to be receiving morenutrients than are removed in a year. Focuswinter grazing and high-intensity grazing onfields that would benefit from increased fertil-ity levels.

3. Minimize potential for runoff on fields withhigh soil test phosphorus. Reducing thepotential for runoff from the fields can reducethe effects of elevated soil test phosphorus lev-els on surface water quality. High soil test phos-phorus only reduces water quality if runoffreaches a stream from the field. Avoid buildingsoil test phosphorus levels on fields prone tohigh runoff and erosion rates.

Prevent excessive buildup of nutrients in soilAs soil test levels increase, the concentration in

the runoff water from the field also increases.Managing pastures to limit excessive buildup of soiltest p will improve water quality.

Dairies have the potential to increase soil testphosphorus through grazing activities if they feedhigh amounts of concentrates and feed additives(Table 10.1). Fields with a long history of manureapplication usually have high soil test levels. Thefollowing activities will minimize the buildup ofsoil test phosphorus on pastures. Summary

.Nutrient flow in dairy pastures differs fromnutrient flow in many other agricultural fields.Some fields may accumulate nutrients fromgrazing activities. Understanding the sources ofnutrients for each field will help identify thefields with the greatest need or greatest excessof nutrients.

.Cows are fertilizer applicators in grazing sys-tems. Increasing grazing intensity helps cowsmore uniformly distribute manure around the

pastures..Runoff from agricultural fields is a major con-

tributor to water pollution in many lakes andstreams. Mismanagement dramatically increasesthe loss of nutrients from agricultural systems.

1. Do not overfeed nutrients to cattle. Excessnutrients fed to cows pass through the animalinto the manure. On farms with excessive nutri-ent levels, overfeeding nitrogen and phospho-rus adds unneeded nutrients into the manure,which exacerbates the problem. Surveys inWisconsin show most dairy rations are signifi-candy above the optimum phosphorus concen-tration for milk production. Every 0.1-percentincrease in phosphorus concentration above theanimal's need increases phosphate excreted by40 lb.

2. Rotate areas used for winter grazing orreceiving the highest intensity grazing.

MISSOURi DAIRY GRAZING MANUAL