Soil Science Society of America Journal 64:365-370 (2000)
© 2000 Soil Science Society of America
DIVISION S-6-SOIL & WATER MANAGEMENT & CONSERVATION
Water Use and Yield of Limited-Irrigated and Dryland Corn
Charles A. Norwooda
a Southwest Research-Extension Center, 4500 E. Mary, Garden City, KS 67846 USA
cnorwood{at}oz.oznet.ksu.edu
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ABSTRACT
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Corn (Zea mays L.) is grown on more irrigated hectares than any crop in the Great Plains. Much of this area is irrigated from the Ogallala aquifer, which is being depleted in some areas, particularly in the central and southern portions of the region. Research was conducted at Garden City, KS, from 1994 through 1997 to evaluate the effects of various combinations of irrigation, N rate, and plant population on water use and yield of corn and to determine if limited irrigation is a viable alternative to returning irrigated hectares to dryland in an area of declining groundwater. Treatments were zero, one, two, and three irrigations, each consisting of 150 mm of water, applied to corn grown with conventional tillage (CT) and no tillage (NT). Appropriate N rates and plant populations were used with each irrigation treatment to give the management systems S0, S1, S2, and S3. The single irrigation was at tassel (VT) and the two irrigation treatment was at VT and at the dough stage of grain fill (R4). Corn irrigated three times received a vegetative irrigation at the 9 to 10 leaf stage (V9) plus irrigations at VT and R4. Management system S1 increased yield by an average of 1.76 Mg ha-1 or 29%. On average S2 and S3 increased yields an additional 11 and 13%, respectively. No till increased yield and water-use efficiency (WUE) in 2 of 4 yr. On average NT increased yield by 0.56 Mg ha-1, and WUE by 0.96 kg ha-1 mm-1 . Conclusions are that corn will produce adequate yields with one or more irrigations; thus, limited irrigation combined with proper fertility and plant population is a viable alternative to dryland in an area of declining groundwater.
Abbreviations: CT, Conventional tillage • NT, no tillage • R4, dough stage • S0 through S3, management systems 0 through 3 • V9, 9-leaf stage • VT, tassel stage • WUE, water use efficiency
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INTRODUCTION
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CORN OCCUPIES MORE IRRIGATED HECTARES in the Great Plains than any crop. Much of this area is irrigated from the Ogallala aquifer, which stretches across parts of eight states, Texas, Oklahoma, New Mexico, Kansas, Colorado, Nebraska, Wyoming, and South Dakota. A summary of the statistics obtained from the web sites of the Departments of Agriculture from these states reveals that more than 3.5 million ha of irrigated corn are grown above the Ogallala aquifer. Parts of the aquifer have undergone substantial declines since extensive ground water irrigation development began about 1940. By 1980, water levels in parts of the Texas High Plains, Oklahoma Panhandle, and southwestern Kansas, an area having about 0.7 million ha of irrigated corn, had declined by more than 30 m (Dugan and Sharpe, 1995). The decline has slowed in much of the area, averaging about 0.034 m yr-1 from 1980 through 1994. However, the decline has increased in Kansas, averaging 0.13 m yr-1 since 1980.
The decline in the aquifer, coupled with increasing pumping costs, has resulted in considerable research on limited, rather than full, irrigation for the crops in the region. In Nebraska, Hergert et al. (1993) reported corn yields of 5.6, 10.1, and 11.8 Mg ha-1 for dryland, limited irrigation, and full irrigation, respectively, and marginal returns of 31 kg ha-1 mm-1 for limited irrigation and 11 kg ha-1 mm-1 for full irrigation. Stone et al. (1987, 1993) found that the traditional preplant irrigation of corn did not result in additional yield over that resulting from an in-season irrigation in western Kansas. Also in western Kansas, Hooker (1985) reported that two timely irrigations for grain sorghum [Sorghum bicolor (L.) Moench] did not reduce yields markedly compared to three irrigations. In the Texas Panhandle, Stewart et al. (1983) devised a graded furrow system, which included full irrigation at the upper half of the field, tailwater for the next one quarter, and dryland for the remaining one quarter of the field. This system increased grain sorghum yield by an average of 0.15 Mg ha-1 for each 10 mm of irrigation, compared to 0.09 Mg ha-1 for conventional irrigation.
Several researchers have studied the relation of cropping systems to irrigation. Norwood (1995) found that more wheat (Triticum aestivum L.) or grain sorghum can be produced in western Kansas with very limited irrigation than with dryland systems, but no single system was best for all conditions. Producers with less water probably should irrigate crops in fallow systems, while those with more water can crop more intensely. Chanyalew et al. (1989) suggested that as the water table declines in western Kansas, less irrigated corn and more dryland grain sorghum should be grown. Their model indicated that the irrigated crop should be corn, rather than the less water intensive grain sorghum. Recent research by Norwood and Currie (1997, 1998) suggests that the dryland crop also could be corn.
Conservation tillage systems have been used to conserve irrigation water and improve WUE. Unger and Wiese (1979) reported that sorghum in an irrigated winter wheat-dryland cropping system in the Texas Panhandle produced more grain with NT than with tillage. Wiese et al. (1998) reported that NT increased precipitation storage during fallow, grain sorghum yield, and irrigation WUE. Christenson et al. (1994) found grain sorghum yields were significantly higher with NT in New Mexico and partially attributed the increase to water conserved by the NT crop residue later in the season. Beneficial effects of residue management on irrigated corn have been demonstrated in such diverse locations as the Texas Panhandle (Unger, 1986) and the Piedmont (Wagger and Cassel, 1993).
Irrigation water can be conserved and yields maintained by using irrigation timing to avoid stress at critical growth stages. In Minnesota, work by Johnson et al. (1987) showed that irrigated corn responded as well to midseason irrigation as it did to more frequent irrigations at 50% soil water depletion. In Washington, Robins and Domingo (1953) found that soil water depletion to the wilting percentage at tassel or pollination for 1 to 2 d reduced yield 22%, and for 6 to 8 d, by 50%. Similarly, Denmead and Shaw (1960) in Iowa reported that stress at silking reduced yield 50%, whereas stress during the vegetative stage and after silking reduced yields by 25 and 21%, respectively. In the Texas Panhandle, Musick and Dusek (1980) also found stress during tasseling and silking to be the most harmful, but stress during grain filling was more harmful than stress during vegetative growth. At Bushland, TX, Eck (1984) found that 14 and 28 d of stress during the vegetative stage reduced corn yields by 23 and 46%, respectively. Plant water stress during the vegetative growth stage reduced yield by reducing seed numbers, whereas stress during grain filling usually resulted in lower seed weight. In western Kansas, Darusman et al. (1997) reported that drip irrigation resulted in near-maximum corn yield and reduced drainage losses below the root zone when irrigation and rainfall totaled 75% evapotranspiration (ET, the sum of water transpired by the crop and evaporated from the soil surface). In their study, 100% ET was about 500 mm, thus, the saving was 125 mm of irrigation water.
The purpose of this study was to evaluate the effects of management systems with different levels of irrigation, N fertilizer, and plant populations on water use and yield of corn and to determine if these systems with limited irrigation are a viable alternative to returning irrigated hectares to dryland in an area of declining ground water.
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Materials and methods
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The research was conducted at the Southwest Research Extension Center near Garden City, KS, from 1994 through 1997. The soil type was a Ulysses silt loam (fine-silty, mixed, superactive, mesic Aridic Haplustoll) with a pH of 7.8 and an organic matter content of 15 g kg-1. Long-term average climatic data for Garden City are: precipitation, 455 mm; mean temperature, 12°C; open pan evaporation (April–September), 1808 mm; and frost-free period, 170 d. Rainfall during the study period is presented in Table 1
. Corn was planted in the wheat–corn–fallow system, which allows two crops in 3 yr. Wheat was planted in late September of each year and harvested in late June of the following year. Corn was planted in early- to mid-May in the stubble remaining from the previous wheat crop and harvested in late September to early October. Thus, fallow periods of about 11 mo occurred between harvest and planting of each crop. Only the corn phase of the study will be discussed. Three sequences of plots were used so that corn could be harvested in each year. Conventional tillage and NT were used. The CT plots were bladed with a sweep plow about four times during fallow to control weeds. Herbicides were used to control weeds in the NT plots. Atrazine [ 6 - c h l o r o - N - e t h y l - N ' - ( 1 - m e t h y l e t h y l ) - 1 , 3 , 5 - t r i a z i n e - 2 , 4 - d i a -mine] at a rate of 2.2 kg ha-1 (all rates are expressed as active ingredient) was applied after wheat harvest to the NT corn plots to be planted the next spring. This was followed by 2.2 kg ha-1 metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] + 1.1 kg ha-1 atrazine about 5 to 10 d before planting. Appropriate rates of the postemergence herbicides glyphosate [N-(phosphonomethyl)glycine] and 2,4-D [(2,4-dichlorophenoxy)acetic acid] were tank mixed with the residual herbicides in the NT plots if weeds were present at application. The CT plots received the same preplant herbicides, but tillage was used for existing weeds instead of postemergence herbicides.
Treatments consisted of four management systems (hereafter referred to as systems), S0, S1, S2, and S3, each consisting of an irrigation treatment combined with the appropriate level of plant population and fertility (Table 2)
. Due to confounding of treatments, plant population, fertility, and irrigation effects cannot be determined separately, so only the effects of the combination of these three factors are discussed. Irrigation treatments were zero, one, two, or three irrigations, each consisting of a metered amount of 150 mm of water applied through gated pipe. The plots were bordered to prevent runoff. The corn was irrigated at various growth stages as defined by Ritchie et al. (1997). The single irrigation was done when the tassel was becoming visible (between V18 and VT). Two irrigations were done between V18 and VT and at approximately R4 (dough stage). The system consisting of three irrigations received the two previous irrigations plus an early irrigation during the vegetative stage when most plants were in the V9 to V10 growth stages. Plant populations and N rates were applied to each system according to anticipated yields. Yields were expected to range from about 5 Mg ha-1 for S0 to 10 Mg ha-1 for S3. Ammonium nitrate was broadcast preplant each year at rates of 80, 112, 140, and 160 kg N ha-1, for S0, S1, S2, and S3, respectively. Fully irrigated corn in the region usually receives at least 225 kg N ha-1 and can yield in excess of 12.5 Mg ha-1. The limited irrigated corn in this study required less N, and was grown after fallow, reducing the required rate of fertilizer N somewhat due to mineralization during the fallow period. `Garst 8714'1
corn, a hybrid having 105-day maturity, was planted with a Buffalo slot planter at seeding rates of 45000 plants ha-1 for S0 and S1 and 58000 plants ha-1 for S2 and S3. A population of 45000 plants ha-1 has proven optimum for dryland in southwest Kansas (Norwood and Currie, 1996). Optimum populations for limited irrigation are unknown, but 58 000 plants ha-1 for two and three irrigations (S2 and S3) was chosen, rather than higher populations, to avoid some of the effects of anticipated heat and drought stress. Fully irrigated corn in the region is usually planted at about 75000 to 87500 plants ha-1. Moreover, a short-season hybrid was chosen for this limited-irrigated study rather than one of the 116 to 120 d (full-season) hybrids usually grown under full irrigation because these dry conditions were expected to reduce yield, particularly with only one irrigation.
The experimental design was a split plot with three replications. System was the main plot treatment and tillage was the subplot treatment. Each system plot was 12 m (16–75 cm rows) wide by 32 m long; thus each tillage plot was eight rows wide. Grain yields were obtained by hand harvesting the corn from two 9-m row sections from the center of each plot. The samples were shelled and weighed, and yields were corrected to 15.5 g kg-1 moisture. Soil samples were taken in 0.3-m increments to a depth of 1.8 m at planting and harvest for the determination of soil water content. Only water in the profile as a whole is discussed, not the individual increments. Ulysses silt loam has a water-holding capacity of about 600 mm in a 1.8-m profile, approximately 300 mm of which is available. Overall WUE's for each system were determined by dividing the grain yield by the water used (sum of soil water at planting soil water at harvest + irrigation water + precipitation). System WUE's were expressed as the increase in yield per 150 mm increment of irrigation water. Due to confounding, the effects of irrigation could not be determined separately, thus WUE, as used in this paper, includes the effects of N and plant population.
The data were analyzed by analysis of variance and regression. If analysis of variance resulted in significant F values, means were separated by lsmeans (SAS Institute, 1998).
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Results and discussion
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Precipitation
Precipitation during the study period is presented in Table 1. It was above average in all years and during the May through September growing seasons. However, precipitation was slightly below average during the July through September portion of the 1995 growing season. Growing-season deviations ranged from 26 mm in 1994 to 136 mm in 1995. The best precipitation distribution during the growing season occurred in 1996, and the months having the most precipitation were May 1995 and August 1997.
System
No system by tillage interactions occurred, so the data presented in the tables are averaged over tillage. The top portion of Table 3
shows yield data from the 4 yr of the study. Yields ranged from <5 Mg ha-1 for the dryland (S0) treatment in 1997 to about 11 Mg ha-1 for the S3 treatment in 1994. The lower portion of Table 3 shows preplanned yield comparisons expressed as differences between pairs of treatments. Except for the S3 vs. S1 comparison the data also can be interpreted as system WUE expressed as Mg ha-1 yield per 150 mm increment of water. Overall WUE's are discussed below. System 0 increased yield an average of 1.76 Mg ha-1 (29%). The smallest response to system occurred in 1996, and the reason is not clear. Soil water at planting (Table 7)
was lowest in 1996, and the poor planting conditions delayed emergence. No precipitation occurred until 9 d after planting when 46 mm fell. Plant stands were satisfactory, and distribution of precipitation was excellent throughout the remainder of the growing season, yet yields were lower than expected. The largest responses to all systems occurred in 1997. On average, the smallest responses occurred when S2 vs. S1 were compared. In 1995 and 1996, S2 did not differ significantly from S1. However, the response of S3 over that of S1 was highly significant (P < 0.001) in all years, and the response of S3 vs. S2 was less than
only in 1996.
Results are presented graphically in Fig. 1
, with curves showing the highest r2 value at P < 0.10. The 1994 and 1997 data best fit quadratic equations, and the 1995 and 1996 data best fit linear equations. The curves indicate that maximum yield was not obtained (or expected) with the combination of irrigation water, N rate, and plant populations used in this study.
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Fig. 1 Corn yield as affected by irrigation. Data points indicate Mg ha-1 resulting from 150 mm of irrigation water applied zero, one, two, and three times, incombination with the N rates and plant populations given in Table 2.  ,**,*** indicate significance at P < 0.10, 0.01, and 0.001, respectively
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Whereas irrigation, N rate and plant populations were the only measured sources of variation in each year, soil water at planting and growing-season precipitation were also sources of variation across years (Table 4)
. The data best fit an equation that included a quadratic component for precipitation. The R2 value indicates that the three factors accounted for 85% of the variation in yield. System had the most effect, according to the standard estimates. These estimates (also called standard partial regression coefficients) can be used to determine the relative importance of each variable in determining yield, with larger values indicating more effect (Steel and Torrie, 1960). Thus, system was about 1.8 times as important as soil water at planting and 1.7 times as important as precipitation (sum of the linear and quadratic components) in determining yield.
Considerable water remained in the profile after harvest (Table 5) . The Ulysses silt loam in this study retains about 300 mm of unavailable water in the 1.8 m profile, so the values shown indicate that the non-irrigated profiles were nearing depletion in 3 of 4 yr. The amount of water remaining in the soil profiles usually increased with the number of irrigations. However, no differences occurred in S2 vs. S1 in 1995 and 1997 or in S3 vs. S2 in 1996. The amount and distribution of rainfall resulted in more water remaining in the profile at each irrigation level in 1996 than in other years. Norwood (1995) found considerable water in the profile following irrigated wheat and sorghum. Although this water was available for the following crop, yield increased only 20% of the time in that study. Water remaining in the profile may drain below the root zone, if enough precipitation occurs during the subsequent fallow period. Soil water measurements were not taken below 1.8 m in this study, but Stone et al. (1987) found drainage losses to be negligible from a similar soil at Tribune, KS, unless available profile water content exceeded 50%. Available water often exceeded 50% in the current study after the estimated 300 mm unavailable water was subtracted from the amounts of water remaining from three irrigations (See Table 7). Darusman et al. (1997) determined that drainage was reduced substantially with irrigation amounts <396 mm. Thus, in the current study, two irrigations (300 mm) probably did not cause much water loss (except in 1996), but with three irrigations (450 mm) drainage may have occurred below the root zone. In 1996, drainage probably occurred even with one irrigation. The loss of water is important particularly in areas of a declining water table. A farmer should apply no more water than the crop can use. The data suggest that if a farmer has enough water to irrigate more than once a longer season hybrid should be used. Although similar water use rates have been reported for both short- and long-season corn (Trooien et al., 1999; Howell et al., 1998), total water use is higher for long-season corn because of later maturity. A long-season hybrid was not used because favorable climatic conditions throughout the duration of this study were not expected. Higher plant populations would also have increased yield and depleted more soil water.
Unlike the previously discussed data, overall WUE exhibited no particular pattern (Table 6)
. Positive differences in WUE, of course, were associated with larger yields in proportion to the amounts of water used, and the opposite was true for negative WUE. The largest increase in WUE, 3.40 kg ha-1 mm-1, occurred for the S1 vs. S0 comparison in 1997. This increase corresponds to the largest yield increase of the 4 yr (Table 3). The only other significant increases in WUE occurred for S1 vs. S0 in 1994 and S3 vs. S2 in 1995. The largest reduction in WUE was 3.94 kg ha-1 in 1996 for the S3 vs. S1 comparison. In the remainder of the comparisons, WUE either was reduced or not significantly affected by system. Thus, although system increased yield, in this particular study it usually did not result in increased WUE. A comparison of the yield data in Table 3 and the WUE data in Table 6 indicates that of 14 yield increases, three were accompanied by increased WUE, four by decreased WUE and seven by unchanged WUE. On average, system caused negative WUE differences in two of the four comparisons, and no difference in the other two comparisons. Less growing season rainfall might have given different results.
Tillage
Soil water at planting was significantly higher in the NT plots in 3 of 4 yr, but significantly lower in the NT plots in 1995 (Table 7). However, only 6 mm less soil water was present in NT in 1995, and only 8 mm more in 1997. The only meaningful differences occurred in 1994 and 1996, when NT had 48 and 31 mm more soil water at planting, respectively. On average, 20 mm more soil water was present in the NT plots. No significant system by tillage interactions occurred. No-tillage resulted in highly significant increases in yield and WUE in 1995 and 1996, but only in 1996 did these increases follow more soil water at planting. Thus, soil water at planting alone was not a good predictor of yield in this study. On average, NT resulted in a yield increase of 0.56 Mg ha-1 and a WUE increase of 0.96 kg ha-1 mm-1. These increases indicate the potential of NT to increase yield even with irrigation. The increases in yield and WUE in 1995 that occurred in the absence of additional soil water at planting may have been due to water conserved by crop residue in the growing crop, as suggested by Christenson et al. (1994).
More soil water at harvest remained in the NT treatments in 3 of 4 yr. These increases occurred in the same years as increased soil water at planting; thus, not all of the additional water stored with NT was used by the crop. These additional amounts were small but may indicate that NT corn can be irrigated less than CT corn, as suggested by Unger (1986).
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Conclusions
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Irrigation, fertilizer, and plant population management systems substantially increased yields above those of dryland corn. A single irrigation at VT combined with 112 kg ha-1 N increased yield by an average of 1.76 Mg ha-1 (29%). On average, two (VT + R4) and three (V9 + VT + R4) irrigations, in combination with increased N rates and plant populations increased yields by an additional 11 and 13%, respectively. No-till increased yield in 2 of 4 yr, but more soil water at planting resulted in a yield increase in only 1 yr. Across years, the management system used was about twice as important as soil water at planting and precipitation in accounting for variation in yield. The corn hybrid used in this study did not use all the water in the profile when irrigated more than once, and water loss below the root zone probably occurred with three irrigations. This indicates that a longer-season hybrid with a higher yield potential and greater water use should have been used. Yields and WUE from a longer-season hybrid would have been higher. Absence of visible stress indicates that higher plant populations could have been used. However, the favorable climatic conditions during all 4 yr of this study were not anticipated. Results will probably differ under drier conditions.
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NOTES
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Kansas Agric. Exp. Stn. Contribution no. 99-345-J. Research supported in part by a grant from the Kansas Corn Commission.
1 Mention of a trade name does not imply endorsement by Kansas State University over comparable products. 
Received for publication February 19, 1999.
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ABSTRACT
INTRODUCTION
