Simulation of irrigation requirements for majorcrops in South Western Quebec

J. GALLICHAND1, R.S. BROUGHTON1, J. BOISVERT2 and P. ROCHETTE2

1Department ofAgricultural Engineering, Macdonald College ofMcGill University, Ste~Anne~de-Bellevue, PQ, Canada H9XICO; and Land Resource Research Centre, Research Branch, Agriculture Canada, Ottawa, ON,Canada K1A 0C6.Received 24January1990; accepted 4 July 1990.

Gallichand, J., Broughton, R.S., Boisvert, J. and Rochette, P. 1991.Simulation of irrigation requirements for major crops in SouthWestern Quebec. Can. Agric. Eng. 33:001-009. Supplemental irrigation is important in south western Quebec to ensure maximum cropproduction. This study was conducted to determineirrigationrequirements for major crops grown in this area. Soil moisture simulationswere performed using the Versatile Soil Moisture Budget version IVin order to quantify irrigation requirements for nine crops and threesoil types using meteorological records from ten stations. Weeklywater deficits were determined at five probability levels. Resultsshowed that crops grown on loamy sand exhibit a wider range ofvariation in year to year irrigation requirements when compared tocropsgrownon clay loam. Maximumrooting depth androot development affect the magnitude and distribution of water deficits within thegrowing season. Tables of peak and seasonal irrigationrequirementsthat can be used for irrigation system design are presented.

L'irrigation d'appoint est importante dans le sud-ouest du Quebecpour assurer des recoltes maximales, Cette etude a ete effectuee pourdeterminer les besoins d'irrigation des principales cultures de cetteregion. Le Bilan Versatile version IV a ete utilise pour simuler lateneur en eau du sol de facon a quantifier les besoins d'irrigation deneuf cultures sur trois types de sol en utilisant les donneesmeteorologiques de dix stations. Les deficits en eau hebdomadairesont ete calcules pour cinq niveaux de probability. Les resultats mon-trent que les besoins annuels d'irrigation varient beaucoup plus pourles cultures sur sable loameux que pour celles sur loam argileux. Laprofondeurmaximale d'enracinement et le developpement des racinesaffectent l'intensite et la distribution des deficits en eau. Des tableauxpresentant les besoins d'irrigation de pointe et saisonniers ont etedeveloppespour assister a la conception des systemes d'irrigation.

INTRODUCTION

The south western part of Qu6bec is a vital area for theproduction of vegetables and grain corn. Figure 1 shows thatsupplemental irrigation is important in south western Quebecto ensure maximum crop production. Quantified water deficitsare essential as a planning tool for the development of watermanagement strategies, and as a basis for design of irrigationsystems and reservoirs.

Water deficits in Quebec have been studied in the past 25years by various authors (Chapman and Brown 1966; Coligadoet al. 1968; Lake and Broughton 1969; Baier and Robertson1970; Massin 1971; Sly and Coligado 1974). All these studiesare based on simple soil moisture models that either do nottake into account the effect of specific crops on evapotranspiration or take the actual evapotranspiration as a fixed fractionof the reference evapotranspiration. While such an approach isuseful as a comparative tool in identifying areas that require

CANADIAN AGRICULTURAL ENGINEERING

more attention, it is of limited use for design of irrigationsystems and dimensioning of irrigation reservoirs.

STATIDN» VALLEYFIELD 36 YEARS

• EVAPDTRANSPIRATIDN

JULY AUGUST SEPT.

A PRECIPITATION

Fig. 1. Average evapotranspiration and precipitation for astation representative of south western Quebec.

Only three of the above mentioned studies dealt specifically with irrigation requirements. Coligado et al. (1968)provided tables of weekly water deficits at various probabilitylevels using 30 years of data for two stations in south westernQuebec, while Lake and Broughton (1969) analyzed five stations using 18 years of data. Results of studies on peak andseasonal irrigation requirements are also presented by Baierand Robertson (1970), but none of the stations studied arelocated in south western Quebec .

The objective of this paper is to present a method fordetermining weekly irrigation water requirements using improved soil moisture modeling techniques andevapotranspiration estimation, and to summarize results formajor crops grown in south western Qu6bec.

SELECTION OF STATIONS, CROPS AND SOILS

Ten stations located within 80 km from Montreal were used in

this study. Their location and identification are shown in Fig.2. Table I presents general information about the stations used.The time period available for analysis at each station variedfrom 22 to 72 years with eight of the ten stations having morethan 30 years of data. For stations SGM, SRL, and JLT between one and three years were missing in the time periodshown in Table I. Since the JLT station moved from one

location to another, the database for this station was created by

Fig. 2. Locaton of study area and meteorological stations.

combining data from both locations.Stations with long meteorological records (LST, SRL, JLT)

were checked for consistency. Earlier years would have beendiscarded if a time trend had been apparent. However, visualexamination of graphs showing year by year variations ofseasonal precipitation and evapotranspiration did not presentsucha trend, and therefore data from all years were kept.

Nine crops were chosen for analysis. Six of them werevegetables (cabbage, broccoli, carrots, onions, lettuce, andcelery); the others were corn, soybeans, and potatoes. Since itwasnot intended to analyze irrigation requirementsof specificcrop varieties, general values of crop properties (e.g. rootingdepth, planting date, length of growing season) were used.Vegetables were included in this analysis because they areoften irrigated due to their high economic value. Potatoes aregrown in sandy soils and are therefore prone to water deficits.Sprinkler irrigation is not widely used for corn and soybeansinQu6bec. However, eachyear largerareas of these twocropsare subsurface irrigated where water is available and condi-

Table I. Information on meteorological stations.

600

SAND~T LOAMY1 SANDYSAND LOAM

LOAM SILTY I CLAYLOAM LOAM

SOIL TEXTURE

sandyT~clayCLAY

(adapted from Cote, 1982)

Fig. 3. Water holding characteristics for a range ofmineral soils.

tions are suitable.

Two mineral soils (loamy sand and clay loam) and oneorganic soil were selected for analysis. As shown in Fig. 3, themineral soils chosen represent two extremes in terms of available water. Valuespresented in Fig. 3 were established usingvolumetric water content from Cote (1982) and bulk densitiesfrom Hansen et al. (1980). TableII summarizes water holdingcharacteristics of the three selected soils. Characteristics forthe organic soil were taken from Boelter (1964) and Parent(personal communicationwith L.-E. Parent, DepartementdesSols, Universit6 Laval, Ste-Foy, PQ).

SOIL MOISTURE MODEL

Research on irrigation requirements by Coligado et al. (1968)and Baier and Robertson (1970) is based on a computer program described in Baier and Russelo (1968). The maindrawback of the soil moisture model used in this program is

Longitude Latitude

west north Altitude

AMSL

(m)

Number

of

yearsStation (degrees minutes) Period

SDB 73 56 45 26 39 1941-1987 47

HTG 74 10 45 03 49 1952-1987 36

SCD 73 41 45 10 56 1947-1987 41

SHT 72 58 45 37 31 1941-1987 47

LST 73 26 45 49 21 1931-1987 57

VFD 74 06 45 16 46 1952-1987 36

FLR 73 00 45 48 30 1967-1988 22

SGM 72 46 45 43 44 1963-1988 251SRL 73 07 46 02 15 1915-1988 722JLT3 1915-1988 714

(a) 73 26 46 02 59

(b) 73 25 46 00 46

Year 1966 missing,

2Years 1956 and 1986 missing,Database forJLT (Joliette) has been created by combining datafrom (a)Joliette and(b) Joliette-Villestations,

4Years 1956,1962 and 1978 missing.

GALLICHAND, BROUGHTON, BOISVERT, and ROCHETTE

Table II. Water holding characteristics for the threeselected soils.

Water content (mm/m)

Permanent Field

wiltingpoint capacity Saturation

Available

water

(mm/m)

Loamy sand

Clay loam

Organicsoil

97 167

186 439

230 720

400

490

840

70

253

490

that theactualevapotranspirationis taken as a fixed fractionofthe reference evapotranspiration fortheentire growing season,while inreality theratio of actual toreference evapotranspiration varies from crop to crop and from one growing stage toanother for a given crop.

The Versatile Soil Moisture Budget version IV (VB-IV)(Boisvert et al. 1990) has been usedin this study to determinethe irrigation requirements. The VB-IV is a refinement of anearlier soil moisturemodel described by Baier and Robertson(1966), and has proven effective in modeling soil moisturecontent for a variety of crops, soils, and climatic conditions(Selirio and Brown 1979; Baier et al. 1980; Dyer and Mack1984; Teixeira de Faria et al. 1987).

TheVB-IV divides thesoilprofileintotwodrainage zones,each of which is composed of soil layers that can vary innumber and depth. The soil water balance is performed on thesoil layers, while the drainage zones are used for modelinginfiltration and drainage phenomena. The only climate relatedinputs required are thedailyprecipitation andreference evapotranspiration.

Available water below the root zone will move upward bycapillary flow when the water content in the root zone decreases, in much the same way as irrigationwater is providedto crops by subirrigation. For this reason, the depth of soilconsidered in the simulationswas defined by adding 20 cm tothe maximum crop rooting depth. The maximum rootingdepthswereestablished in consultation with agronomistsfrom

Table III. Crop related characteristics.

the Ministfere de l'Agriculture, des Pdcheries et del'Alimentation du Quebec, and are presented in Table III foreach crop-soil combination for which simulations were performed. The soil profile was assumed homogeneous and wasdivided into six layers, 5,7.5, 12.5,25, 25, and 25 percent ofthe soil profile depth, with the thinner layer at the soil surface.The upper drainable zone consisted ofthe first three soil layersin thecase of the clay loam soil, and of the first four layers inthe case of the loamy sand and organic soil.

EVAPOTRANSPIRATION

An accurateestimate of actual evapotranspiration is essentialin modeling soilmoisture content. Actual evapotranspirationis a function of climatic factors (netradiation, vapor pressuredeficit, wind speed, and air temperature), crop factors (croptype, growing stage, root density distribution), and soil factors(soiltexture, watercontent). With theVB-IV theactual evapotranspiration is calculated by

ETa =

where:

ETa

n

Act, Ksi

ETo

Ev

1= 1

Ksim ETo + £v (1)

= actual evapotranspiration (mm/d),= number of layers in the soil profile,= crop and soil coefficients, respectively of the

ith soil layer,= grass reference evapotranspiration (mm/d), and= additional evaporation from the wetted soil

surface which occurs after heavyrainfalls (mm/d).

Each of the factors on the right hand side of Eq. 1 will bediscussed in the following sections.

Reference evapotranspiration (ET0)

The effect of climate on crop water requirements is given by

Maximum rooting Crop coefficients Fraction of R1Initial depth (cm) available

rooting water clay loamdepth loamy clay organic initial mid-season end of readily loamy or organic

Crop (cm) sand loam soil stage stage maturity available sand soil

Com 5 100 80 .* 0.51 1.05 0.55 0.60 0.40 0.75Soybeans 5 60 50 - 0.51 1.00 0.45 0.50 0.50 0.75Potatoes 5 40 - - 0.51 1.05 0.70 0.25 0.75 .

Cabbage 10 50 40 - 0.48 0.95 0.80 0.45 0.55 0.75Broccoli 5 50 40 - 0.48 0.95 0.80 0.45 0.55 0.75Carrots 5

- - 70 0.48 1.00 0.70 0.35 . 0.75

Onions 5 - - 30 0.49 0.95 0.75 0.25 . 0.75Lettuce 5 - - 30 0.49 0.95 0.90 0.30 . 0.75Celery 10

- - 30 0.49 1.00 0.90 0.20- 0.80

* an •-' indicates crop-soil combinations that were not studied,see Figure 4 for a graphical definition of R.

CANADIAN AGRICULTURAL ENGINEERING

the grass reference crop evapotranspiration (ETo) which isdefined as the rate of evapotranspiration from an extensivesurfaceof 8 to 15 cm tall green grass cover of uniform height,actively growing, completely shading theground andnotshortof water (Doorenbos and Pruitt 1977).

Previous studies on irrigation requirements (e.g. Coligadoet al. 1968; Massin 1971) used either the Thornthwaite (1948)or a slightly modified version of the Baier and Robertsonequation (Baier and Robertson 1965; Baier 1971) to calculatethe reference evapotranspiration. The Baier and Robertsonequation is expressed as:

ETo= -5.39 + 0.157 Tmax + 0.158 Range + 0.109 Qo (2)

where:

Tmax = maximum daily temperature (°C),RANGE = difference between maximum and minimum

daily temperature (°C),QoETo

-2.J-K= extraterrestrial radiation (MJ«m «d ), and= reference evapotranspiration (mm/d).

The Penman equation (Penman 1963) is the most adequateto estimate accurately the reference evapotranspiration.However, there are very few stations in Quebec where therequired input parameters have been measured. Working withmeteorological records from May to September, Rochette(1988) modifiedthe BaierandRobertsonequationto minimizedifferences with the Penmanequation. The resulting equationcan be expressed as:

ET0 = a(ao + a\ Tmax + aiXRANGE + asQo) (3)where:

XRANGE = RANGE - NRANGE (°C),NRANGE = long term monthly averageof RANGE (°C),0O,ai,02,03 = regression coefficients that vary with location

and average daily summer wind run,a =oto +ai DM + oc2 DM2 + +a?DM1,a0,...,oc7 = regression coefficients basedon location, andDM = number of days after May 1st.

Comparisons between ET0 values calculated with Eq. 3andthe Penman equation resulted in a maximum daily averagedifference of 0.1 mm (3.6%).

For the months of May to September Eq. 3 was used tocalculate ET0> while for April and October Eq. 2 was used.Long term monthly averages of minimum and maximum temperatures were taken from Environment Canada (1982) andaverage daily summer wind run from the Ministfcre deTEnvironnement du Qu6bec.

Crop coefficients (Kc)

The crop coefficient represents the effect of crop on evapotranspiration andis a function of crop type andgrowing stage.Figure 4 shows a generalized crop coefficient curve ofthe typeusedin this analysis.Kc valuesat maturity, and for initialandmid-season stages were determined using themethod given inDoorenbos and Pruitt (1977), and are presented in Table III.Dates defining each stage were established with farmers and

l.£ -i

OL / .^

u 1.0 - >• /! 1

* >.,_a >-

Zu 0.8 - L3

Z

a

>•a

i- a< <

< X X(_) X

•-•

u.

Z<_l

*

z

a \llu.

0.6 -a. 2 a.

*-

• | 1 x <(J L

ini—

t^

0.4 -

O | 1 CROP .

INITIAL DEVELOPMENT 1 MID--SEASON MATURITY 1

0.2 - r 1 11 1V /

r

CRDP GROWING STAGES

0 - 1 1 "T 1 1 1APR 1 MAY 1

JUNE JULY1

AUG1

SEPT 1 DCT '

(AFTER DDDRENBQS AND PRUITT, 1977)

Fig 4. Generalized crop coefficient curve.

local agronomists of the Ministfere de 1'Agriculture, desPfecheries et de TAlimentation du Qu6bec.

The VB-IV requires crop coefficients for each soil layer ofthe soil profile and allows variation of crop coefficients foreach soil layer at any time during the crop growing season.The Kc value of a given layer depends on the Kc value of thecomplete soil profile, layer thickness, and percentage of rootspresent in that layer. Crop coefficients presented in Table IIIwere distributed in the six soil layers so that

Kt

i = l

(4)

The distribution was performed in two steps. Firstly, toreflectthehigher rootdensity nearthesoilsurface, the rootingdepth wasdividedinto four root layersof equal thickness, andto each of these layers was assigned a crop coefficient valuecorresponding to 40, 30, 20, and 10 % of the Kc value. Although the distribution of root density with depth may varywithsoilsandcrops,theabovedistribution is representative ofa homogeneous profile (Hansen et al. 1980). Secondly, theseroot layer crop coefficients were adjusted to fit thesoillayering pattern. A linear evolution of the rooting depth wasassumed betweenplanting or transplanting and the end of thecrop development stage.

Forthecomplete soilprofile, themaximum evapotranspiration, ETm, is defined as:

ETm = /. Kci' ET0 + EV (5)

The maximum evapotranspiration is equivalentto the actualevapotranspirationif the crop is never short of water, that is, ifirrigation water is applied when needed.

Soil coefficients (Ks)

The rate of evapotranspiration is affected by the amount ofwater in the soil. Evapotranspiration occurs at the maximumrate down to a given fraction of the available water, /?, thendecreases linearly. This relationship is shown in Fig. 5.Curves developed by Baieret al. (1979) suggest anR value of

GALLICHAND, BROUGHTON, BOISVERT, andROCHETTE

0.75 for clay loam soils and 0.25 for loamy sand soils. Fororganic soils a R value of 0.75 has been used.

Crop coefficients and soil coefficients based only on soiltype fail to take into account that notall crops have the sameability to extract soil moisture. Soil coefficients used in thispaper take into consideration this limitation and can be viewedas soil-crop coefficients. However, the term soil coefficienthas beenkept for simplicity.

Doorenbos and Pruitt (1977) present the fraction of available water that is readily available for a number of crops. Forexample, 60% of the available water is readily available forcorn (R = 0.40) compared to 25% for potatoes (/? = 0.75). Inorder to account for this factor when defining the soil coefficient curve, the R value was selected by taking whichever ofthe crop or soil was most restrictive. Selected R values arepresented in Table III for the various crop-soil combinationsanalyzed. Figure 5 presents a sample case for potatoes grownon loamy sand. In this case, even though the loamy sand allowsunrestricted evapotranspiration down to a water content corresponding to 25 percent of the total available water,evapotranspiration will be reduced when the water content ofthe soildrops below 75 percent because after thispointwaterisnotreadily available topotatoes. Therefore, for this particularsoil-crop combination, the more restrictive Rvalue of 0.75was selected.

Evaporation (Ev)Evaporation is increased after irrigation or rainfall (Wright

l.U -

* 0.8 - \£ZLi

U.R value for

potatoes on• 0.4 -u

_J

8 0.2-

0 1 1 l 1 1

1.0 0.8 0.6 0.4 0.2 0

FRACTION OF AVAILABLE WATER REMAINING IN SDIL

Fig. 5. Relationship between soil coefficient and fractionof available water still in soil.

1981). VB-IV increases the actual evapotranspiration for dayswhen the water content of the surface layer is greater thanfield capacity. This additional evaporation (£v) has a maximum value of ET0 - [Kc Ks ET0] but never exceeds thedepthof waterin excessof fieldcapacityin that layer.

METHOD OF ANALYSIS

Selection of crop-soil-station combinations

Crops are not grown irrespective of the soil type. This hasbeen taken into consideration when determining which crop-soil combinations should be analyzed. Crop-soil combinationsthat were not considered are identified in Table III. Further

more, due mainly to soil geographical distribution, theproduction of some crops is concentrated in a number ofgeographical areas. For this reason not all crops were analyzedat each of the ten meteorological stations. Table IV presentsfor each crop the meteorological stations for which simulations were performed.

Soil moisture simulations

The growing season foreach cropis shown in Fig. 6. In southwestern Quebec snowmelt and late winter precipitation provide more than enough water to bring soil water content tofield capacity. Therefore, soil moisture simulations werestartedwith thesoil profileat fieldcapacityon April29, exceptfor early planted lettuce (April 22). Broccoli, lettuce, andcelery are planted at intervals. To detect the peak irrigationrequirements of these crops, three planting dates were established : early, mid-season, andlateplanting. Cabbage isstartedin nurseries, and celery in greenhouses, then transplanted inthe field at dates shown in Fig. 6. When required,crop coefficients of the initial stagewere usedbetween April 29 and theplanting ortransplanting date. Soil moisture simulations terminated at the end of the crop growing season.

Calculation of irrigation requirements

Irrigation requirements were calculated from daily soil watercontents simulated by theVB-IV using observed precipitationand calculated reference evapotranspiration. The term irrigation requirements, IR, or water deficit, is used in thispaper torepresent the amount of water needed, in addition to thatprovided by rainfall, inorder for the crop toevapotranspire atthe maximum rate.

Table IV. Combinations of crops and meteorological stations used for analysis.

Crop SDB HTG SCD SHT LST VFD FLR SGM SRL JLT

Corn X* X X X X X X X X X

Soybeans X X X X X X X X X X

Potatoes X X X X X X X X X X

Cabbage X X XX

Broccoli X X XX

Carrots X X X

Onions X X X

Lettuce X X X

Celery X X X

.

: an'x' indicates crop-meteorological station combinations that were analysed.

CANADIAN AGRICULTURAL ENGINEERING

CRDP MAR APR MAY JUNE JULY AUG SEPT OCT

CORN

SOYBEANSPOTATOES (early variety)POTATOES «ate variety)

CABBAGEBROCCOLI (early planting)BROCCOLI (nld-season planting)BROCCOLI date planting)CARROTS

ONIONSLETTUCE (early planting)LETTUCE mid-season planting)LETTUCE (late planting)CELERY (early planting)CELERY (nld-season planting)CELERY (late planting)

1 1

Fig. 6. Growing season for each crop.

//?= ETm-ETa (6)

Irrigation water will be needed whenever the soil coefficient, Ks, becomes less than 1.0. When this happens, the cropcannot evapotranspire at its maximum rate, and yields lessthan maximum results.

The VB-IV program was modified to provide, in additionto ETa, ETm values as defined by Eq. 5. Daily irrigationrequirement values were accumulatedover 7-day intervals toprovide weekly irrigation requirements.

For each week in the crop season, irrigation requirementvalues were arranged in ascending order for the number ofyears analyzed. The probability, p, that a given irrigationrequirement value, //?,, will be exceeded is:

p = (N-Ni)/N (7)where:

N = total number of years analyzed, andNi = rank number corresponding to an irrigation

requirement value smaller than, or equal to IRi.

Weekly irrigation requirement values corresponding toprobability levels of 0.1 (l-in-10 dry year), 0.2 (l-in-5 dryyear), 0.5 (median year), 0.8 (l-in-5 wetyear), and0.9 (l-in-10wetyear) were determined. Foreach probability level, peakand seasonal irrigation requirements were also established.

RESULTS AND DISCUSSION

A total of 116 simulations were performed to cover all crop-soil-meteorological station combinations. For eachsimulation, graphs and tables were prepared giving weeklyirrigation requirements at probability levels of 0.1, 0.2, 0.5,0.8, and 0.9. Figs. 7, 8, and 9 present sampleresults for cornand potatoes.

Figures 7 and 8 are typical of the differences observedbetween clayloam and loamy sand. Loamy sandsoils displaya wideryear to year variation in irrigationrequirement values.The median year irrigation requirement is higher for loamysandthanfor clay loam,but wetteryears (p = 0.8 and0.9) tendto result in higherwater deficits for clay loamthan for loamysand. Thisphenomenon canbeexplained bythelower percentage of available water that is readily available in clay loamsoils(i.e.higher/?value). Even though clay loam soilshavea

larger reserve of available water than loamy sand soils, cropsgrown on clay loam soils will suffer from alarger water deficitwhen the soil water content fluctuates justbelow field capacity.

As can be seen in Figs. 7, 8, and 9, water deficits areexperienced early in the growing season for crops grown inclay loam and loamy sand. This is due to the small amount ofwater available toplants when their roots are shallow. As theroots develop, more water isavailable. This explains the slightdecrease in water deficit a few weeks after planting, which isnoticeable especiallyfor crops grownon loamy sand.

Maximumrooting depth is another factor affecting the extent of water deficits. Shallow rooted crops tend to suffer morefrom water deficits than deep rooted crops. This can be ob-

CDRN DN CLAY LOAM STATIDN -. VALLEYFIELD

APR MAY JUNE JULY AUG SEPT OCT

NOTE : curves are ordered (upper to lower) as followsp = 0.1, 0.2, 0.5, 0.8, and 0.9

Irrigation requirements for corn on clay loam.CDRN DN LDAMY SAND STATIDN : VALLEYFIELD

Fig. 7

Zu

LdOHl—i *^s

a * 80Ld 0;

• E

P ~ 10

S 5a:

35

30

25

APR MAY JUNE JULY AUG SEPT DCT

NDTE i curves are ordered (upper to lower) as followsp = 0.1, 0.2. 0.5, 0.8, and 0.9

Fig. 8. Irrigation requirements for corn on loamy sand.

PDTATDES (LATE) DN LDAMY SAND STATIDN s VALLEYFIELD

\

A /-'A\\

/ \ s. \\

r\ M X

/ s~rx-V NVJ V CA.

APR MAY JUNE JULY AUG SEPT DCT

NDTE : curves are ordered (upper to lower) as followsp = 0.1, 0.2, 0.5, 0.8, and 0.9

Fig. 9. Irrigation requirements for potatoes on loamysand.

GALUCHAND, BROUGHTON, BOISVERT, and ROCHETTE

35PDTATDES (LATE) DN LDAMY SAND ALL STATIONS served by comparing results for corn (Fig. 8), which has a

maximum rooting depth of 100 cm on loamy sand, to resultsfor potatoes (Fig. 9), for which the maximum rooting depth is40 cm.

Irrigation requirements for a given crop-soil combinationwere comparable from station to station. Variations in irrigationrequirement valueswerelargerforcaseswhereallstationswere included than where only three or four stations werestudied. As a sample of this variation, Fig. 10 shows theenvelope of weekly irrigation requirements for potatoes onloamy sand at probability levels of 0.1,0.5, and 0.9.

The peak irrigation requirement of a crop-soil combinationis the highest water deficit occurring during one or moreweeks of the growing season, whereas, the seasonal irrigationrequirement is the total water deficit during the growing season. Average values and range of variation from station tostation of peak and seasonal irrigation requirements are pre-

(AH-ZIdXu

o * 20

D C

Pv 10

i-i 5aa:

~ 0

30

25 0 %i^P

M Wfo#J01

m$> /A,%*&& ^^iw

APR MAY JUNE JULY ' AUG SEPT ' DCT

YZ777& p = o.i S888888H p = 0.5 R^^l p = 0.9

Fig. 10. Extent of station to station variation in irrigationrequirements for potatoes grown on loamy sand.

Table V. Peak irrigation requirements.

Crop1

Corn

Com

SoybeansSoybeans

Potatoes (Ev)

Potatoes (Lv)

CabbageCabbage

Broccoli (E)Broccoli(E)

Broccoli(M)Broccoli(M)

Broccoli (L)

Broccoli (L)

Carrots

Onions

Lettuce (E)Lettuce (M)

Lettuce (L)

Celery (E)Celery (M)Celery (L)

Peak irrigation requirements (mm/week)

p=0.1 p=0.5

oil

pe2 Average Range Average Range

CL 13.4 11.2-16.1 8.3 6.3-10.5

LS 24.6 21V7-27.3 13.4 9.1-18.2

CL 18.2 16.1-21.7 13.2 11.2-15.4

LS 27.0 24.5-30.8 15.5 11.9-19.6

LS 30.7 27.3-36.4 18.3 16.8-21.7

LS 29.1 26.6-31.5 18.5 16.1-21.7

CL 10.3 8.4-11.2 6.3 4.9-70

LS 18.2 16.1-18.9 6.1 3.5-7.7

CL 15.6 14.0-16.8 10.9 9.8-11.9

LS 24.0 22.4-25.2 13.7 10.5-15.4

CL 9.3 7.0-10.5 5.1 4.2-5.6

LS 17.7 14.7-18.9 5.8 3.5-7.7

CL 4.0 3.5-4.9 0.2 0.0-0.7

LS 7.4 7.0-7.7 1.2 0.7-2.1

O 3.0 2.1-3.5 0.5 0.0-0.7

O 12.1 11.9-12.6 5.4 4.2-6.3

0 8.4 7.7-9.1 2.3 2.1-2.8

0 5.8 4.9-6.3 1.6 0.7-2.1

0 1.9 1.4-2.1 0.0 0.0-0.0

0 14.0 13.3-14.7 7.0 5.6-8.4

0 12.4 11.9-12.6 6.1 4.9-7.0

0 6.3 4.0-7.0 2.3 1.4-2.8

1Ev and Lvidentify early and late potatoes variety, E, M and L identify early, mid-season and late planting,CL =clay loam; LS = loamy sand; O - organic soil.

CANADIAN AGRICULTURAL ENGINEERING

Table VI. Seasonal irrigation requirements.

Crop1

Com

Com

SoybeansSoybeans

Potatoes (Ev)

Potatoes (Lv)

CabbageCabbage

Broccoli (E)

Broccoli(E)

Broccoli(M)Broccoli(M)

Broccoli (L)Broccoli (L)

Carrots

Onions

Lettuce (E)

Lettuce (M)

Lettuce (L)

Celery (E)Celery (M)Celery (L)

Soil

type2 Average

Seasonal irrigation requirements (mm/week)p=0.1 p=0.5

Range Average Range

Ev and Lv identify early and late potatoes variety, E, Mand Lidentify early, mid-season and late planting, +CL=clayloam; LS =loamy sand; O =organic soil.

sented for twoprobability levels(0.1 and0.5) in Tables V andVI. From these tables, it can be seen that at both probabilitylevels potatoes have the highest peak and seasonal irrigationrequirements, while late planted lettuce has the lowest. Thegeneral trend for vegetables planted and harvested at intervals(broccoli, lettuce, celery) is thathigher irrigation requirementsareobserved at thebeginning of thegrowing season.

Peak irrigation requirements (Table V) can be used fordesign of irrigation equipment, whereas seasonal values(Table VI) can be taken as a basis for estimating requiredvolumes of irrigation reservoirs. Irrigation requirements forother soil types can be estimated by interpolation based onvariations of available water presented in Fig. 3. Values presented in Tables V and VI represent the amount of waterneeded by thecrop only. They donottake into account irrigation water losses due toinefficiencies of the irrigation systems

CL 146.6 114.1-172.9 74.4 49.7-97.3

LS 267.7 215.6-301.7 84.2 54.6-116.2

CL 210.5 177.8-241.5 134.4 106.4-164.5

LS 335.4 293.3-361.9 126.0 82.6-168.0

LS 257.9 231.0-290.5 127.1 96.6-159.6

LS 341.0 305.2-368.2 150.7 110.6-189.0

CL 108.9 95.9-114.8 53.9 44.1-59.5

LS 178.5 158.2-192.5 42.7 26.6-57.4

CL 92.1 81.9-97.3 49.9 42.0-54.6

LS 177.8 162.4-189.0 66.3 52.5-74.2

CL 71.2 58.8-77.0 30.8 22.4-37.1LS 135.8 117.6-149.8 32.9 18.9-48.3

CL 21.2 16.1-25.9 0.2 0.0-0.7LS 44.6 39.2-47.6 2.6 1.4-4.2

O 26.6 18.9-33.6 2.1 0.0-4.2

O 113.6 101.5-121.1 41.3 31.5-49.7

O 28.0 24.5-32.2 5.1 4.2-6.30 31.3 24.5-35.0 5.1 2.8-6.30 7.5 4.9-9.1 0.0 0.0-0.0

0 97.8 89.6-105.0 40.4 32.2-49.7O 99.4 88.9-105.7 39.0 32.2-43.4O 52.5 42.7-58.8 11.2 6.3-14.7

or non-uniformities in water application.Values of Tables V and VI are adequate forplanning pur

poses. However, generalized crop and soil properties havebeen used and therefore, variations in irrigation requirementsmust be expected when a specific crop variety is grown in aparticular soil. If the Versatile Soil Moisture Budget were tobe used for the purpose of irrigation scheduling, soil profilecharacteristics and cropparameters suchas crop coefficientsand root distribution and depth would need to be defined moreprecisely.

SUMMARY AND CONCLUSIONS

Soil moisture simulations were performed toanalyze irrigationrequirements of corn, soybeans, potatoes, and six vegetablesgrown in southwestern Quebec. Irrigation requirements were

GALUCHAND, BROUGHTON, BOISVERT, andROCHETTE

determined for loamy sand, clay loam, and organic soils. Tenmeteorological stations within 80 km from Montreal, withrecord lengths varying from 22 to 72 years were selected forthe analyses. The Versatile Soil Moisture Budget version IVwas used since it has proven effective in simulating soil watercontent for a range of soils, crops, andclimatic conditions inCanada.

Results showed that a wider range of variation in the year-to-year irrigation requirements occur for crops grown on loamysand asopposed to clay loam.The magnitude and variations ofirrigation requirements during thegrowing season isalso affectedbycrop rooting characteristics. Forcropsgrownonclayloamandloamy sand, water deficits areexperienced early in the growingseasonas a result of a shallow root system.

Since irrigation requirement values were of comparablemagnitude from station to station, tables giving peak andseasonal irrigation requirements for the median and l-in-10dry year were developed as a guide for designing irrigationequipment and reservoirs.

The procedure used in this paper to obtain irrigation requirements is applicable to other subhumid areas of the worldfor planning of irrigation systems. However, the use of theVersatile Soil Moisture Budget for irrigation schedulingwould require the development of local crop coefficients andthe definition of site specific parameters suchasrootdistributionanddepth, and soil profilecharacteristics.

REFERENCES

BAIER, W. 1971. Evaluation of latent evaporation estimatesand their conversion to potential evaporation. Can. J. PlantSci. 51:255-266.

BAIER, W., J.A. DYER and W.R. SHARP. 1979. The versatilesoil moisture budget. Tech. Bull. 87. Agrometeorology Section,Research Branch, Agriculture Canada, Ottawa, ON. 52p.BAIER, W. and G.W. ROBERTSON. 1965. Estimation oflatent evaporation from simple weather observations. Can. J.Plant Sci. 51:276-284.

BAIER, W. andG.W. ROBERTSON. 1966. A new versatilesoil moisture budget. Can. J. Plant Sci. 46:299-315.BAIER, W. and G.W. ROBERTSON. 1970. Climatic estimates of average and probable irrigation requirements and ofseasonal drainage in Canada. J. Hydrol. 10:20-37.BAIER, W. and D.A. RUSSELO. 1968. A computer programfor estimating risks of irrigation requirements from climaticdata. Tech. Bull. 59. Agrometeorology Section, ResearchBranch, Agriculture Canada, Ottawa, ON. 48 p.BAIER, W., J.C. ST. PIERRE and J.H. LOVERING. 1980.Analysis of environmental factors affecting timothy yields.Agric. Meteorol. 22:319-339.BOELTER, D.M. 1964. Water storage characteristics of several peats in situ. Soil Sc. Soc. Proc. 28:433-435.BOISVERT, J.B., J.A.DYERandD.BREWIN.1990. Versatile soilmoisture budget reference manual - VB4. Tech. Bull. ResearchBranch, Agriculture Canada, Ottawa, ON. (in preparation).CHAPMAN LJ. and D.M. BROWN. 1966.The climate of Canada for agriculture. Report No. 3. The Canada Land Inventory.Environment Canada, Lands Directorate, Toronto, ON. 24 p.

CANADIAN AGRICULTURAL ENGINEERING

COLIGADO, M.C., W. BAIER and W.K. SLY. 1968. Riskanalyses of weekly climatic data for agricultural and irrigationplanning: L'Assomption, PQ. (Tech. Bull. 26); Lenoxville,PQ (Tech. Bull. 27). Agrometeorology Section, ResearchBranch, Agriculture Canada, Ottawa, ON. 8 p.COTE, D. 1982. Les fagons culturales. Conseil des Productions Vdg6tales du Quebec - Sols. Quebec, PQ. 42 pp.DOORENBOS, J. and W.O. PRUITT. 1977. Guidelines forpredicting crop water requirements. FAO Irrigationand Drainage paper 24. Food and Agriculture Organization of theUnited Nations, Rome, Italy. 144 p.

DYER, J.A. and A.R. MACK. 1984. The versatile soil moisture budget, version three. Contribution No. 82-33. LandResource Research Institute, Research Branch, AgricultureCanada, Ottawa, ON. 24 p.

ENVIRONMENT CANADA. 1982. Canadian climate normals. Vol. 2. Temperature, 1951-1980. AtmosphericEnvironment Service, Ottawa, ON. 306 p.

HANSEN, V.E., O.W. ISRAELSEN and G.E. STRINGHAM.1980. Irrigation principles and practices. 4th ed. John Wiley& Sons, New York, NY. 417 p.

LAKE, E.B. and R.S. BROUGHTON. 1969. Irrigation requirements in south western Qu6bec. Can. Agric. Eng.11:28-31,38.

MASSIN, B. 1971. Les deficits hydriques au Qu6bec. Publ.M.P.-34. Direction Gen6rale des eaux, Ministfcre desRichesses Naturelles, Gouvernement du Qu6bec, Quebec,PQ. 284 p.

PENMAN, H.L. 1963. Vegetation andhydrology. Tech.Com-mun. No. 53. Commonwealth Bureau of Soils, CAB, FarnhamRoyal, Bucks, England. 124 p.ROCHETTE, P. 1988. Contributions au zonageagroclimatique du Quebec meridional. Ph. D. Thesis.Departement de Phytologie. Facult6 des Sciences der Agriculture et de 1' Alimentation, University Laval, Ste-Foy,PQ. 264 p.

SELIRIO, I.S. andD.M.BROWN. 1979. Soil moisture-basedsimulation of forage yield. Agric. Meteorol. 20:99-114.SLY, W.K. and M.C. COLIGADO. 1974. Agroclimatic mapsfor Canada - derived data: Moisture and critical temperaturesnear freezing. Tech. Bull. 81. Agrometeorology Research andService, Chemistry and Biology Research Institute, ResearchBranch, Agriculture Canada, Ottawa, ON.29 p.TEIXEIRA de FARIA, R., A.C.S. da COSTA, K. MAIDA andJ. BOISVERT. 1987. Performancede un modelo matemdticopara predi?ao de umidade do solo. In: O clima odesenvolvimento rural brasileiro. Fifth Brasilian Congress ofAgrometeorology, Londrina, Brasil. pp. 69-73.THORNTHWAITE, C.W. 1948. An approach toward a rational classification of climate. Geogr. Rev. 38:55-94.

WRIGHT, J.L. 1981. Cropcoefficients forestimatesof dailyevapotranspiration. In: Irrigation scheduling for water andenergy conservation in the 80's. Proc. Irrigation SchedulingConference. Pub. 23-81. Am. Soc. Agric. Engrs., St. Joseph,MI. pp. 22-26.