Irrigated agriculture in the Central Great Plains

Transcription

1 RESOURCE ALLOCATION IN CORN PRODUCTION WITH WATER RESOURCE CONSTRAINTS R R. Lamm, M. E. Nelsn, D. H. Rgers MEMBER MEMBER ASAE ASAE ABSTRACT. Crn (Zea mays L.) is the irrigated crp f chice fr many irrigatrs in the Central Great Plains, but it requires significant amunts f irrigatin water t prduce high yields. Declining water resurces in sme areas have resulted in increased public scrutiny f crn irrigatin practices. Sme irrigatrs are respnding by practicing deficit irrigatin f crn, even thugh it is ecnmically risky and smetimes cmplicated t successfully implement, A three-year study was initiated in the fall f 1985 n a Keith silt lam sil (Aridic Argiustll) in nrthwest Kansas t determine the agrnmic and ecnmic feasibility f nine different resurce-allcatin management schemes fr irrigated crn. Irrigatin timing and amunt, nitrgen fertilizatin, and crn seeding rate were the three allcated resurces. Average crn yields ranged frm 6,09 t 9,98 Mglha (97 t 159 bu/acre) with average irrigatin amunts ranging frm t 380 mm (4 t 15 in,). Fully irrigated crn using the standard recmmended seeding rate and full fertilizatin had a higher net incme than did any f the ther resurce-allcatin schemes fr deficit-irrigated crn. This scheme nt nly maximized the mean net incme but als minimized the standard deviatin f net incme. Assuming a crn cash market price f $ kg ($2.25 J bu), there was an apprximately $2851 ha ($7001 acre) difference between the highest and lwest net incmes fr the varius management schemes. Management-induced variatins in crp prductin caused a much greater shift in net incme than did variatins in resurce csts amng the management schemes, emphasizing the need fr resurce-allcatin management schemes that prduce high crn yields. If irrigatin is limited, mderate amunts f water stress hardening during the crn vegetative stage with prper matching f the fertilizer and seeding rate will stretch the irrigatin seasn. This type f management scheme increased crn yields by 20% when the water allcatin was restricted t mm (6 in.). Federal farm deficiency payments had a marked effect f changing the prfitability status frm negative t psitive fr seven f the nine management schemes, when the crn cash market price was $ kg ($1./bu). Keywrds. Irrigatin management. Irrigated agriculture in the Central Great Plains imprves net farm incme and prvides mre ecnmic stability fr a regin ften subject t drught. Irrigatin develpment in the Central Great Plains ccurred in areas with little municipal r industrial use f the water. Irrigatin management generally prvided water fr fully irrigated crp prductin. As irrigatin develpment cntinued, mre marginal water resurces were develped, and verdevelpment f sme surces ccurred. During the same time, ther water uses have becme mre imprtant as urban areas seek t meet water needs. Article was submitted fr publicatin in December 1992; reviewed and apprved fr publicatin by the Sil and Water Div. f ASAE in April Presented as ASAE Paper N Cntributin N J frm the Kansas Agricultural Experiment Statin. The mentin f trade names r cmmercial prducts des nt cnstitute their endrsement r recmmendatin by the authrs r by the Kansas Agricultural Experiment Statin. The authrs are Freddie R. Lamm, Assistant Prfessr and Research Agricultural Engineer, M. E. Nelsn, Assciate Prfessr and Extensin Agricultural Ecnmist, Nrthwest Research-Extensin Center, Kansas State University, Clby; and Danny H. Rgers, Assciate Prfessr and Extensin Agricultural Engineer, Dept. f Agricultural Engineering, Kansas State University, Manhattan. Irrigatin systems and management techniques have respnded t cnserve limited water supplies and maintain ecnmic prductivity. Changing physical and institutinal cnstraints cntinue t require new r different methds t allcate water. Scientists and water planners have examined many different methds fr using water efficiently. Many factrs can affect management schemes, such as water supply, irrigatin capacity, crp yield ptential, crp-marketing pprtunities, dryland crpping alternatives, structure f individual state water law, federalfarm prgrams and even farmer preference. When irrigatin water supply is the majr cnstraint, management takes int accunt the available crpping system alternatives, available land area t be irrigated, and any peculiarities impsed if the cnstraint is institutinal. Cnstraints n water use can be single-seasn r multiseasnal. Bernard et al. (1988), using a multiseasnal simulatin mdel t simulate a surface-irrigated farm in the Clumbia River Basin, reprted a 40% reductin f annual water allcatin culd be impsed withut a severe impact n net farm incme. Martin et al. (1989) develped a dynamic prgramming mdel t annually allcate a limited water supply ver a multiseasnal perid. This mdel can als be used t help prducers chse the crrect mix f crps and balance f irrigated and nnirrigated land. A water-banking system implemented in suthwest Nebraska, limiting the amunt VOL. 9(4): JULY American Sciety f Agricultural Engineers / 93 /

2 f water utilized in a five-year perid, prvides an excellent pprtunity t utilize this mdel. Martin and van Brcklin (1985) reprted multiseasnal allcatin decisins depend n whether the bjective is t maximize net incme r t maximize the lwest annual net incme during the perid. Maximizing net incme will favr using the water earlier in the perid. Reducing the risk f a lw net incme will favr saving sme f the water fr a drier than nrmal year. Crp rtatins can result in mre efficient use f limited irrigatin supplies (Schneeklth et al., 1991). Rtatin f a higher irrigatin-use crp, such as crn, with a lwer irrigatin-use crp, such as wheat, allws efficient use f residual sil water and increases the effective strage f verwinter precipitatin. Rtatins als permit a higher rati f irrigated t nnirrigated area. The advantage is reduced yield variatin due t drught because a larger area receives sme irrigatin. In western Kansas, crn yields have increased dramatically ver the last 20 years and at a much higher rate than grain srghum yields. Grain srghum prductin can be marginal because f cl nighttime temperatures at the higher elevatins. Crn is a majr feed grain fr the large red meat industry in Kansas. These factrs, cupled with federal farm prgrams, make crn the irrigated crp f chice fr mst western Kansas prducers. Hwever, deficit irrigatin f crn is a questinable enterprise. Yields usually decrease when irrigatin is less than required t meet the full evaptranspiratin requirements f crn. In an irrigated-crn study in the Suthern High Plains, Eck (1986) fund water stress reduced yields but did nt increase water-use efficiency. He cncluded deficit irrigatin f crn was nt feasible fr that area. Musick and Dusek (1980) in a study at Bushland, Texas, reached a similar cnclusin, stating "limited irrigatin f crn shuld nt be practiced." Stewart et al. (19), althugh nt thrughly discunting the practice, admitted that limited irrigatin f crn is much mre cmplex than limited irrigatin f grain srghum. They cncluded water stress during the reprductive and early grain-filling stages shuld be avided, unless there was a cnditining r stress-hardening perid during the vegetative stage. Rhdes and Bennett (1990) reprted after reviewing numerus studies, that water stress impsed at any grwth stage n crn will generally lwer the efficiency f the water used in transpiratin. Still, western Kansas irrigatrs desire t grw crn and, in many cases, are practicing deficit irrigatin. Prducers are familiar with crn prductin techniques and are smetimes reluctant t change t alternative crpping systems. Kansas water law ties an irrigatin water right t a parcel f land, s there are sme practical cncerns t using irrigated and nnirrigated rtatins n the same parcel f land. A three-year study was initiated in the fall f 1985 t determine the ptential fr deficit irrigatin f crn, by nt nly managing the allcatin f irrigatin, but als nitrgen fertilizatin and plant ppulatin. The study did nt determine the ptimum fertilizatin and plant ppulatin within a given irrigatin cnstraint. Rather it sught t evaluate several pssible management schemes in terms f net incme. Fertilizer and seeding rates incrprated int the varius irrigatin management schemes were based n previus experience with crn prductin in nrthwest Kansas. PROCEDURES The prject was cnducted frm 1985 t 1988 at the KSU Nrthwest Research-Extensin Center at Clby, Kansas, n a deep, well-drained, lessial Keith silt lam (Aridic Argiustll). This medium-textured sil, typical f many western Kansas sils, is described in mre detail by Bidwell et al. (1980). The 1.5-m (5-ft) sil prfile will hld apprximately 250 mm (10 in.) f available water at field capacity crrespnding t a vlumetric sil water cntent f apprximately 0.30 and a prfile bulk density f apprximately 1.3 gm/cm 3 (81 lbs/ft 3 ). The climate is semi-arid with an average annual precipitatin f 474 mm (18.7 in.) and apprximate annual lake evapratin f 1400 mm (55 in.). Daily climatic data used t schedule irrigatin were btained frm a weather statin lcated apprximately 250 m (800 ft) east f the study site. The study was cnducted in a 0.6 ha (1.5 acre) dead level irrigatin basin, apprximately 180 m lng x 30 m wide (600 x ft) with plts 4.6 m wide and 30 m lng (15x ft) running perpendicular t the level basin length. The plts accmmdated six crn rws spaced cm (30 in.) apart. Small dikes were cnstructed arund each plt t prevent runff between plts. The study treatments were replicated three times in a randmized cmplete blck design. The reference evaptranspiratin (ET r ) was calculated using a mdified Penman cmbinatin equatin similar t the prcedures utlined by Kincaid and Heerman (1974). The specifics f the ET r calculatins used in this study are fully described by Lamm et al. (1987). Basal crp cefficients (K cb ) were generated by equatins develped by Kincaid and Heerman (1974) based n wrk by Jensen (1969) and Jensen et al. (1970, 1971). The basal crp cefficients were calculated fr the area by assuming 70 d frm emergence t full canpy fr crn with physilgical maturity at 130 d. This methd f calculating actual evaptranspiratin (AET) as the prduct f K cb and ET r has been applied in past studies at Clby and it has been fund t accurately estimate AET (Lamm and Rgers, 1983, 1985). In cnstructing the irrigatin schedules, n attempts was made t mdify AET with respect t silevapratin lsses r sil-water availability as utlined by Kincaid and Heerman (1974). Nine treatments were devised t examine several reasnable irrigatin schemes within three given cnstraints n ttal water allwance. The irrigatin seasn ceased fr a particular treatment when the irrigatin cnstraint was reached. All plts started the seasn with a full sil water prfile and any applied preseasn irrigatin was nt cnsidered a part f the allwance. Preseasn irrigatin is nt typically needed in nrthwest Kansas. The treatments r management schemes were as fllws, Water allwance nt t exceed mm (18 in.). % f calculated AET % f calculated AET 50% f calculated AET Water allwance nt t exceed mm (12 in.). 380 APPLIED ENGINEERING IN AGRICULTURE

3 % f calculated AET % f calculated AET during vegetative stage, % thereafter 50% f calculated AET during vegetative stage, % thereafter Water allwance nt t exceed mm (6 in.). % f calculated AET % f calculated AET during vegetative stage, % thereafter 50% f calculated AET during vegetative stage, % thereafter Irrigatin water was metered separately nt each plt thrugh gated pipe accrding t the fllwing criteria: Set allwable calculated depletin in the crn rt zne t be t mm (3 t 4 in.). Add rainfall and irrigatin amunts as depsits t the water budget. If depletin amunt is negative, set t zer. Calculate daily actual water use r AET fr crn. (Mdified Penman Equatin with basal crp cefficients) Multiply AET amunt by treatment level percentage t btain mdified AET value fr the particular treatment. Subtract mdified AET value frm water budget fr each treatment. Irrigate a treatment with an amunt equal t the calculated rt-zne depletin when the treatment reaches the allwable calculated depletin. Applicatin efficiency fr the small basins was assumed t be %. The maximum irrigatin rate in the crn study was nt allwed t exceed 7.5 mm/day (0.30 in./d) r a mm (3 in.) irrigatin in a 10-d perid. This maximum irrigatin rate reflected the typical capacity f irrigatin systems in nrthwest Kansas. If the cumulative AET by the crn exceeded the maximum irrigatin rate in a given time perid, the calculated depletin wuld nt be returned t zer after irrigatin. Tassel initiatin was used as the pint at which t shift frm the initial AET factr t the final AET factr fr treatments 5, 6, 8, and 9. The crn was grwn using standard reginal prductin practices fr furrw-irrigated crn with the exceptin f three prductin inputs, nitrgen fertilizer, seeding rate, and irrigatin. Different fertilizer rates and plant ppulatins were used with the different irrigatin schemes t minimize prductin csts. The nitrgen fertilizer (ammnium nitrate, ) was bradcast applied in mid-octber f each year preceding planting in the fllwing spring. Irrigatin treatments with an initial AET factr f % (Trts. 1, 4, and 7) received an actual nitrgen amunt f 235 kg/ha (210 lbs/acre) and were seeded at a rate f 56,800 seeds/ha (23,000 seeds/acre). The % AET factr treatments (Tits. 2,5, and 8) received a nitrgen amunt f kg/ha (180 lbs/acre) and were seeded at a rate f 51,600 seeds/ha (20,900 seeds/acre). Thse treatments scheduled with an AET factr f 50% (Tits. 3, 6, and 9) received a nitrgen amunt f 170 kg/ha ( lbs/acre) and were seeded at a rate f 42,300 seeds/ha (17, seeds/acre). Crn (Pineer brand 3377) was planted n 2 May, 28 April, and 29 April fr 1986,1987, and 1988, respectively Mean Year Figure 1-Summer precipitatin during the study perid and the lng-term mean (1893 t 1991) precipitatin at Clby, Kansas. An apprximately 6-m (20-ft) length f ne crn rw frm the center f each plt was hand harvested in the fall ( , , and ) fr yield determinatin. An enterprise analysis was cnducted by cmparing the ttal incme and prductin expenses f each treatment. Ttal incme assumed a cash market price f $0.089/kg ($2.25 /bu) and a federal farm prgram deficiency payment f $154.43/ha ($62.50/acre). The deficiency payment was calculated as the prduct f an estimated nrthwest Kansas farm prgram yield f 7.85 Mg/ha (125/bu/acre) and the difference between the federal crn target price f $0.108/kg ($2./bu) and the cash market price f $0.089/kg ($2.25/bu). Fixed csts fr land and equipment, including taxes, insurance, interest, and depreciatin ttaling $231.26/ha ($93.59/acre), were btained frm Dhuyvetter and Nelsn (1992) and were held cnstant amng all treatments. An irrigatin energy cst f $0.0141/m 3 ($1.45/acre-in.) f water pumped was used in the analysis and was based n a ttal dynamic head f 7 m (260 ft) and a natural gas price f $0.0795/m 3 ($ /ft 3 ). Nitrgen fertilizer csts were calculated assuming an anhydrus ammnia cst f $0.243/kg ($0.11/lb) f actual nitrgen. Crn seed csts were based n a price f $63.00/bag and 80,000 seeds/bag. Other variable csts (excluding irrigatin energy, nitrgen fertilizer and seed) used in the analysis were labr, pesticides, fuel fr tillage, machinery repairs, crp insurance, crp drying, crp cnsulting, and interest. These csts were als btained frm Dhuyvetter and Nelsn (1992) and ranged amng treatments frm apprximately $440 t $460/ha ($178 t $186/acre) with the small differences being the interest csts assciated with the three changing inputs. RESULTS AND DISCUSSION CLIMATIC CONDITIONS Seasnal precipitatin (May t September) was 324 mm (12.74 in.) in 1986, 352 mm (13.87 in.) in 1987 and 334 mm (13.15 in.) in 1988 which was slightly abve the average seasnal amunt (1893 t 1991) f 321 mm (12.65 in.). In each year ne r mre f the principal grwth mnths, (June, July, r August) had cnsiderably less than the lng term mean (1893 t 1991) precipitatin (fig. 1). The cumulative calculated actual evap- VOL. 9(4): JULY

4 !jj 400 ^ 300 I O Cumulative Calculated AET fr Crn KSU Nrthwest Research Extensin Center / / 4'" Day f Year \ Figure 2-Cumulative calculated water use (AET) f cm fr 1986 t 1988 and the lng term mean (1972 t 1991) at Clby, Kansas. transpiratin (AET) was apprximately 10% greater than the 20-year mean fr bth 1987 and 1988 and was near nrmal fr 1986 (fig. 2). The timing f precipitatin events and evaptranspiratin resulted in net irrigatin requirements fr fully irrigated crn f 380,, and 457 mm (15, 12, and 18 in.) fr 1986,1987, and 1988, respectively (table 1). The net irrigatin requirement fr crn in Thmas Cunty, Kansas, where the study was cnducted, is 391 mm (15.4 in.) with 80% chance precipitatin (Sil Cnservatin Service, 1977). CORN YIELDS AND IRRIGATION Crn yields varied widely amng treatments (table 1) fr the three years f the study, ranging frm a lw f 3.95 Mg/ha (63 bu/acre) fr Treatments 3 and 7 in 1988, the year with the highest irrigatin requirements, t a high f Mg/ha (169 bu/acre) fr Treatment 4 in 1986, the year with lwest, cumulative, seasnal AET. An irrigatin cnstraint f mm (18 in.) f net irrigatin generally will nt limit crn prductin in nrthwest Kansas, as was the case in this study. Averaged ver the three years, fully irrigated (1.00 ET) Treatment 1, fertilized with 235 kg/ha (210 lb/acre) f nitrgen and using a seeding rate f 56,800 seeds/ha (23,000 seeds/acre), had the highest yield f 9.98 Mg/ha (159 bu/acre). Averaged ver the three years, Treatment 1 had significantly higher (P = 0.05) yields than all treatments except fr Treatment 4 and 5. Results fr Treatment 3 illustrate the effect f seasn-lng restrictins in irrigatin. Yields fr Treatments 3 were cnsistently lwer than thse f Treatments 6 and 9, in which irrigatin was restricted nly during the vegetative stage. A similar cmparisn culd be made fr Treatment 2 and 5. Seasnlng restrictin f irrigatin resulted in lwer amunts f irrigatin but als usually resulted in a substantial yield reductin. Tassel initiatin, the end f the vegetative stage, ccurred n 19 July 1986, and n 15 July fr bth 1987 and All treatments with the -mm (12-in.) irrigatin cnstraint (Tits. 4-6) had statistically similar yields in the range f Mg/ha ( bu/acre). These data indicate a gd balance in matching the three resurces f Trt ET Factr ET 2. 0.ET ET ET 5. 0./1.00ET /1.00ET ET 8. 0./1.00ET /1.00ET Mean LSD 0.5 Table 1. Resurce management schemes and their effects n irrigatin requirements and yields f crn, KSU Nrthwest Research-Extensin Center, 1986 t 1988, Clby, Kansas Irrigatin Cnstraint mm (in.) Nitrgen Fertilizer kg/ha (lbs/ acre) 235 (210) (180) 170 () 235 (210) (180) 170 () 235 (210) (180) 170 () Seeding Rate seeds/ ha (seeds / acre) (00) (20900) 40 (17) (00) (20900) 40 (17) (00) (20900) 40 (17) (15) (3) Irrigat in Amunt mm (in.) 1987 (3) 1988 Mean 380 (15) 255 (10) (4) 280 (11) 255 (10) Crn Grain Yield - Mg / ha (bu / a) (159) 9.7 (154) 7.8 (125) 10.6 (169) 10.2 (162) (147) 7.7 (123) 8.7 (139) 8.7 (139) (146) 1.4 (23) (161) 7.6 (121) 6.4 (102) (147) 9.5 (152) 9.0 (143) 7.0 (112) 8.5 (136) 7.5 (120) 8.3 (132) 2.1 (34) (157) 7.8 (125) 4.0 (63) 7.5 (120) 8.0 (127) 7.8 (125) 4.0 (63) 4.6 (74) 6.4 (102) 6.7 (106) 1.6 (25) Mean 10.0 (159) 8.3 (133) 6.1 (97) 9.1 (145) (147) 8.7 (138) 6.2 (99) 7.3 (116) 7.5 (120) 8.0 (128) 1.3 (21) 382 APPLIED ENGINEERING IN AGRICULTURE

5 Date Table 2. Irrigatin dates and amunts fr the varius treatments, 1986 t 1988 Trtl Trt2 Trt3 Trt4 Trt5 Trt6 Tn7 Trt8 Trt9 Treatment Number Jul 7 Jul 25 Aug 7 Aug 13 Aug 20 Aug 28 Ttal 109 (4.28) 110 (4.35) 86 (3.37) 380 (15.00) 78 (3.08) 74 (2.92) 109 (4.28) 110 (4.35) 86 (3.37) mm (in. 78 (3.08) 74 (2.92) ~ (12.00) (12.00) 109 (4.28) 110 (1.72) 78 (3.08) 74 (2.92) 0) c CO v> / 0 03 mm limit 1 0/1 03/1 - mm limit Flx0d$U ftti Ott»rvMri*t>t»its G_ mtngmttu ZZ2 I SSI Ttal 1 0/1 03/1 - mm limit ET Factr and Irrigatin Cnstraint ) c: «c O 1987 Jul 22 Jul 29 Aug 4 Aug 13 Aug 15 Aug 25 Sepl Ttal (12.00) - (12.00) - - _ Figure 3-Prductin csts and ttal incme fr the varius resurceallcatin management schemes fr crn. Net incme is the difference between ttal incme (line) and prductin csts (bars). late date was within apprximately tw weeks frm the end f the irrigatin seasns fr all three years. Average yields fr treatments limited t receiving mm (6 in.) f irrigatin ranged frm 6.21 t 7.53 Mg/ha (99 t 120 bu/a). Under this severe cnstraint, the highest yields were btained when the limited amunt f irrigatin was shifted tward the critical reprductive and grain filling stages (Treatments 8 and 9). Limiting irrigatin during the vegetative stage (Treatment 8 and 9) generally delayed the last irrigatin t abut 20 d later than when full irrigatin (Treatment 7) was applied (table 2) EFFECT OF RESOURCE ALLOCATION ON NET INCOME Jun 22 (3.) ~ (3 ) (3 ) A n enterprise analysis was perfrmed t determine the _ e^ect f resurce-allcatin n net incme. Cash crn _ (3.) (3.) prices, farm prgram payments and fixed csts were held Jul5 7 6 _ cnstant. The ttal csts f the irrigatin energy, nitrgen (3.) - (3.) (3.) - (3.) (3.) - (3.) fertilizer and seed amng treatments ranged frm $88 t Jul is $156/ha ($36 t $63/acre). Other variable csts amng (3.) (3.) - (3.) (3.) - - (3.) - treatments ranged frm apprximately $440 t $460/ha j u l 2 9 _ ^ - - (3Q ( $178 t0 $i86/ acre ) with the small differences being the,, ^ ^ _ interest csts assciated with the three changing inputs. Jul 31 ^,.,, _, ~, t, *. (3.) (3.) (3.) Ttal incme was calculated as the sum f the federal farm Aug i deficiency payment and the prduct f crn yield and cash _ (3.) _ market price. Net incme was calculated as the difference Aug B _ between ttal incme and ttal fixed and variable csts. _ (3.) (3.) ^et j n c m e j s i n fi uenced by the effect f resurce Aug 28 ^ allcatin n bth prductin csts and crp prductin. ^ Althugh minimizing csts is desirable, it is mre G Sep 2., i, t (3.) (3.) _ imprtant t manage and balance the resurce inputs t Ttal btain high crp yields, as illustrated in figure 3. The (18.00) (12.00) (12.00) (12.00) (12.00) hei g h t difference between the ttal incme (line) and ttal csts (bar) equals net incme. The amplitude f the ttal incme line varies much mre than the amplitude f the irrigatin, nitrgen fertilizer and seed within the irrigatin cst bars. Therefre, changes in ttal incme caused the cnstraint. Althugh the average yields fr these three greatest shift in net incme. Prper resurce management, treatments were cnsiderably lwer than fr the fully resulting in high prductin and, therefre, high ttal irrigated Treatment 1, relatively high yields were btained incme, had a greater effect n net incme than the except in 1988, the year with the highest irrigatin needs, differential csts f the resurces. A cmparisn f the irrigatin schedules fr 1986 t 1988 The highest net incme (fig. 3) was btained when (table 2) shws that Treatment 1 and 4 were identical until resurces were nt limited (Treatment 1). Hwever, the VOL. -mm 9(4): (12-in.) - JULY limit 1993 was reached in mid-august. This Treatments 4 t 6, in which irrigatin was limited 383 t

6 ffr c ^ \ Q> e 01 Z. 0 1 Treatment Number Effect f Grain Prices and Farm Prgram J V\ P i w w I \V7/\ tjea/k&js/txia } (OJ009/kg (SZ25/U0\ ES3 $OJ08/kQ($27S/bu>\ FTf m P &_ <D 2: Treatment Number /1 03/1 - mm limit mm limit- 1 0/1 OS/1 mm limit 7 Factr and Irrigatin Cnstraint mm limit- 0/1 0.5/1 1 0/1 05/1 - mm limit mm limit ET Factr and Irrigatin Cnstraint Figure 4-Effect f different grain prices and the presence (dts) r absence (bars) f farm deficiency payment n net incme fr the varius resurce-allcatin management schemes fr crn. Figure 5-Mean annual and standard deviatin f net incme fr the varius resurce-allcatin management schemes fr crn. mm (12 in.), als had psitive net returns and might be acceptable management alternatives if fully irrigated crn was nt an ptin. If the farm prgram deficiency payment were eliminated, nly Treatments 1 and 5 wuld have psitive net incmes f $37.31/ha and $1.61/ha ($15.10/acre and $0.65/acre), respectively, using the assumed cash market price f $0.089/kg ($2.25/bu) and prductin csts. When irrigatin was restricted t mm (6 in.), net incme was negative r very lw fr all treatments even with the farm prgram deficiency payment. EFFECT OF CORN GRAIN PRICE AND DEFICIENCY PAYMENTS ON NET INCOME Further ecnmic analysis was perfrmed t illustrate the effect different grain prices and deficiency payments had n net incmes f the varius management schemes. Farm deficiency and prductin csts were calculated as described in the previus sectin. N management schemes were prfitable assuming a cash market price f $0.069/kg ($1./bu) and n deficiency payment (fig. 4). Hwever, if the deficiency payment was included, seven f the nine management schemes had psitive net incmes. Several prfitable management schemes existed at a cash market price f $0.108/kg ($2./bu), the pint at which the deficiency payment is zer. The prfitability increased dramatically fr Treatments 4, 5, and 6, in which irrigatin was mderately cnstrained t mm (12 in.) as the cash market price increased frm $0.089/kg t $0.108/kg ($2.25/bu t $2./bu). This might make them acceptable alternatives t fully irrigated crn (Treatment 1) if irrigatin were cnstrained. Crn can be grwn with a -mm (6-in.) water allcatin at a lw prfit ptential when the deficiency payment is included but requires careful management f irrigatin, nitrgen fertilizer and seed (Treatment 9 as cmpared t Treatments 7 and 8). When irrigatin allcatins are restricted and result in lw yields belw the farm prgram yield, a paradx can ccur, higher cash market grain prices can result in less net incme (fig. 4). As the market price appraches the federal target price the deficiency payment rate is reduced. Thus when the market price is high and the crp yield is belw the prgram yield, the reductins in deficiency payments are nt fully ffset by the increases in market sales. MEANS AND STANDARD DEVIATIONS OF NET INCOME The means and standard deviatins f net incme were calculated (three replicatins in each f the three years) t examine the average prfit ptential and the variatin f prfit (net incme) fr the varius treatments. Annual irrigatin requirements and crn yields fr the treatments varied and were reflected in the individual calculatins (nine data pints) f the means and standard deviatins f net incme. The standard cash grain price, deficiency payment and prductin csts, as previusly described, were used in this prtin f the analysis. Risk-aversin techniques strive t maximize the mean net incme, while minimizing the standard deviatin f net incme. Analysis f the means and standard deviatins f net incme revealed that the best management scheme was the fully irrigated Treatment 1 (fig. 5). Bth maximum mean and minimum standard deviatin f net incme were btained by Treatment 1. Treatments 3, 7, 8, and 9 shuld be avided because they have the lwest means and highest standard deviatins f net incme. In these schemes, the standard deviatin f net incme is greater than the mean (fig. 5). When mean net incme is psitive, a prducer shuld survive financially in the lng run. Hwever, many prducers wuld nt survive because f the large variatins in annual cash flw. Risk-averse prducers shuld nt practice marginal management schemes. Treatments 2 and 4, althugh pssessing mid-range mean net incmes cmpared t the ther treatments, have standard deviatins higher than the mean (fig. 5). This wuld classify them as relatively risky management schemes, especially when cmpared t Treatments 1, 5 and 6. The analysis revealed that Treatment 5 was best when irrigatin was cnstrained t mm (12 in.). In essence, thugh the differences are nt great, Treatment 5 manages a better balance f resurces than Treatments 4 and 6 as 384 APPLIED ENGINEERING IN AGRICULTURE

7 indicated by the higher mean and lwer standard deviatin (% 5). CONCLUSIONS Fully irrigated crn using the standard recmmended seeding rate and full fertilizatin was fund t be a mre prfitable enterprise than any f the ther resurceallcatin schemes fr deficit-irrigated crn examined in this study. Irrigatrs wishing t cntinue t grw crn when irrigatin is limited by physical (water supply) r institutinal cnstraints shuld seriusly cnsider reducing irrigated land area t match the severity f the cnstraint. This shuld nt be cnstrued t mean that n pprtunities exist t reduce the amunt f water typically used t fully irrigate crn. Many irrigatrs are already upgrading irrigatin systems and management f their present systems t "stretch" water. This des nt result in mre crn prductin fr each unit f water transpired, but because inefficiencies, such as evapratin and perclatin are reduced, mre water is available fr plant transpiratin. If the irrigatin amunt fr a given land area is cnstrained at a deficit amunt, mderate perids f stress hardening during the crn vegetative stage with prper matching f the fertilizer and seeding rate will stretch the irrigatin seasn. This may result in mre water being available fr irrigatin during the critical reprductive and grain-filling stages. Such stretching f the irrigatin seasn increased crn yields by 20% (Treatment 9) when the water allcatin was restricted t mm (6 in.). Net incme is influenced by the effect f resurceallcatin n bth prductin csts and crp prductin. Hwever, at the price levels used in this study, prducers shuld allcate irrigatin, nitrgen fertilizer and crn seed t ensure high prductin rather than t btain significant prductin cst savings. Crp prductin variatins affected net incme much mre than variatins in resurce csts. Federal farm deficiency payments had a marked effect n the verall prfitability f the varius management schemes examined in this study. If the crn cash market price was $0.069/kg ($1./bu) and the deficiency payment was included, seven f the nine management schemes had psitive net incme. N schemes had psitive net incme withut the deficiency payment. Higher grain prices in the range f $0.108/kg ($2./bu) dramatically increased the prfitability f the management schemes in which irrigatin was mderately cnstrained t mm (12 in.) even withut the deficiency payment. Althugh these schemes are still less prfitable than fully irrigated crn, they might be acceptable alternative strategies if irrigatin water is limited. Analysis f the means and standard deviatins f net incme fr the nine management schemes revealed that full irrigatin with the standard recmmended amunts f nitrgen fertilizer and seed was best. This scheme nt nly maximized the mean net incme but als minimized the standard deviatin f net incme. Risk-averse prducers shuld nt practice the severely restricted irrigatin management schemes because the standard deviatin f net incme is greater than the mean net incme, which means large variatins in annual cash flw. Cmparisn f the prfitability f these management schemes fr crn prductin t ther enterprises, such as irrigated wheat r irrigated grain srghum prductin, lies beynd the scpe f the study, s n cnclusins in this area can be drawn r shuld be inferred. REFERENCES Bernard, D. J., N. K. Whitdesey, K. E. Saxtn and D. L. Bassett Irrigatin ptimizatin under limited water supply. Transactins f the ASAE 31 (3): Bidwell, O. W., E. E. Banbury, W. L. Barker and G. E. Muilenburg The Clby Branch Experiment Statin and agriculture in nrthwest Kansas with special mentin f sils. Bulletin 635. Manhattan KS: Agricultural Experiment Statin, Kansas State University. Dhuyvetter, K. C and M. E. Nelsn Rd-irrigated cm. KSU farm management guide, MF-578 revised. Manhattan, KS: Cperative Extensin Service, Kansas State University. Eck, H. V Effects f water deficits n yields, yield cmpnents, and water use efficiency f irrigated cm. Agrn. 7.78: Jensen, M. E Scheduling irrigatin using cmputers. J. Sil and Water Cns. 24(8): Jensen, M. E., C. E. Franzy and D. C. N. Rbb Scheduling irrigatins using climate-crp-sil data. ASCE, J. Irrig. and Drainage 96(IRI): Jensen, M. E., B. J. Pratt and J. L. Wright Estimating sil and misture depletin frm climate, crp and sil data. Transactins f the ASAE 14{5): Kincaid, D. E. and D. F. Heerman Scheduling irrigatin using a prgrammable calculatr. Publicatin ARS-NC-12. Washingtn, DC: U.S. Dept f Agriculture. Lamm, F. R. and D. H. Rgers Scheduling irrigatin using cmputed evaptranspiratin. Presented at the 1983 Midcentral reginal meeting f the American Sciety f Agricultural Engineers. ASAE Paper N. MCR St. Jseph, MI: ASAE. Lamm, F. R. and D. H. Rgers Crn yield respnse t different irrigatin regimes. ASAE Paper N. MCR St. Jseph, MI: ASAE. Lamm, F. R., D. A. Pacey and H. L. Manges Spreadsheet templates fr the calculatin f Penman reference evaptranspiratin. ASAE Paper N. MCR St. Jseph, MI: ASAE. Martin, D. and J. van Brcklin The risk and return with deficit irrigatin. ASAE Paper N St. Jseph, MI: ASAE. Martin, D., J. van Brcklin and G. Wilmes Operating rules fr deficit irrigatin management. Transactins f the ASAE 32(4): Musick, J. T. and D. A. Dusek Irrigated cm yield respnse t water. Transactins f the ASAE 23(l):92-98, 103. Rhdes, F. M. and J. M. Bennett Crn. In Irrigatin f Agricultural Crps, , eds. B. A. Stewart and D. R. Nielsen. Agrnmy Mngraph N. 30. Madisn, WI: ASA- CSSA-SSSA. Schneeklth, J. P., N. L. Klcke, G. W. Hergert, D. L. Martin and R. T. Clark Crp rtatins with full and limited irrigatin and dryland management. Transactins f the ASAE 34{6): Sil Cnservatin Service Kansas irrigatin guide. Salina, KS: Sil Cnservatin Service. Stewart, J. I., R. D. Misra, W. O. Pruitt and R. M. Hagan. 19. Irrigating crn and grain srghum with a deficit water supply. Transactins f the ASAE 18(2): VOL. 9(4): JULY