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Southwest Res. Ext. Cent., 4500 E. Mary, Garden City, KS 67846
* Corresponding author (cnorwood{at}gcnet.com)
Received for publication March 12, 2001.
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Abbreviations: H1, 104-d hybrid • H2, 116-d hybrid • IWUE, irrigation water use efficiency • P1 and P2, low and high plant populations, respectively (see text) • WUE, water use efficiency
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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The declining water levels in the aquifer along with increased pumping costs has resulted in considerable research on limited, or deficit, irrigation. Irrigated hectares may have to be returned to dryland production unless methods can be found to slow the decline of the aquifer, such as developing cropping systems that use water more efficiently. Norwood (1995) found that more wheat (Triticum aestivum L.) or grain sorghum [Sorghum bicolor (L.) Moench] can be produced in western Kansas with very limited irrigation compared with dryland systems, but no single system was best for all producers. Producers with less water probably should irrigate fallow systems while those with more water can crop more intensely. Chanyalew et al. (1989) suggested that as the water table in western Kansas declines, less irrigated corn and more dryland grain sorghum should be grown. Their model indicated that the irrigated crop should be corn, rather than the more drought-tolerant grain sorghum. Recent research by Norwood and Currie (1997)(1998) suggested that the dryland crop could also be corn. Norwood (2000) found that a single irrigation at tassel increased corn yield by 29%. Additional irrigations during the vegetative and grain fill stages increased yield an additional 11 and 13%, respectively. In Nebraska, Hergert et al. (1993) reported corn yields of 5.6, 10.1, and 11.8 Mg ha-1 with dryland, limited irrigation, and full irrigation, respectively, and marginal returns of 31 and 11 kg ha-1 mm-1 for limited and full irrigation, respectively. 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, Trooien et al. (1999) found water use efficiency (WUE) to be greater for limited irrigated crops, but full irrigation of corn was more profitable than limited irrigation.
Irrigation water can be conserved and yields maintained by using irrigation timing 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% water depletion. Denmead and Shaw (1960) in Iowa reported that stress at silking reduced yield by 50%, whereas stress during the vegetative stage and after silking reduced yield 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. Also in the Texas Panhandle, Eck (1984) found that 14 and 28 d of stress during the vegetative growth stage reduced corn yields by 23 and 46%, respectively.
Some researchers have studied corn having different maturities to determine if short-season corn is more water use efficient than long-season corn. In western Kansas, Trooien et al. (1999) found that WUE and water use rate indicated no advantage to switching from longer- to shorter-maturity corn. In the Texas Panhandle, Howell et al. (1998) found short-season hybrids to reduce income and that the reduction in income with a short-season hybrid would be more than six to eight times the saving in irrigation water cost. They suggest that the lost income could be offset by higher grain prices from the early hybrid and the opportunity for grazing a winter wheat double crop.
Comparisons of short- and full-season hybrids have previously focused on whether or not short-season hybrids used less water and whether short- or long-season hybrids use water more efficiently. The amounts of water used in these studies has approached full irrigation. As an example, the research cited above by Trooien et al. (1999) defined limited irrigation as 70% of evapotranspiration. Fully irrigated corn typically receives 500 to 600 mm of irrigation water. Seventy percent of 500 mm is 350 mm of water. The decline in the aquifer has rendered many wells incapable of supplying that amount of water. At this writing, there is discussion in Kansas about maintaining the Ogallala aquifer at zero depletion. Because the natural recharge of the aquifer is negligible, this would effectively put irrigated producers out of business. Research needs to be conducted with hybrids of different maturities that receive only small amounts of water. Therefore, the objectives of this research were to determine (i) if short-season hybrids yield more grain and use less water than full-season hybrids under very limited irrigation and (ii) if limited irrigating of full- or short-season hybrids is more profitable than a conversion to dryland agriculture.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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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 grain yields were corrected to 15.5 g kg-1 moisture. Stand counts, ear counts, and 100-kernel weights were used to determine the yield components ears ha-1, kernels ear-1, and kernel weight. Two soil cores per plot were taken in 0.3-m increments to a depth of 1.8 m at planting and harvest of each crop to determine soil water content. Bulk density measurements were determined in 0.3-m increments to the 1.8-m depth at the beginning of the study. Water content (mm) in each increment was determined by multiplying the gravimetric water content (g kg-1) times the bulk density times the depth of the increment (300 mm). However, only the sum of the increments is discussed. Ulysses silt loam has a water-holding capacity of about 630 mm in a 1.8-m profile, approximately 300 mm of which is unavailable (Harner et al., 1965). Overall WUE was determined by dividing the grain yield by the water used (sum of soil water at planting - soil water at harvest + irrigation water + precipitation) and expressed as kg ha-1 mm-1. Irrigation WUE (IWUE) was expressed as the increase in yield per millimeter of irrigation water. The data were analyzed by analysis of variance and regression (SAS Inst., 1998). If analysis of variance resulted in significant F-values, means were separated by Fisher's LSD.
An economic analysis was conducted using custom rates for tillage, spraying, planting, and harvest operations (Kolterman et al., 2001). Other than pumping and harvest costs, the only differences in the irrigated and dryland budgets were seed, fertilizer, and tillage costs. Seed costs for dryland and irrigated treatments were assumed to be $74.59 and $124.19 ha-1, respectively. Although tillage and fertilizer costs were constant in the actual study, for the purpose of economic analysis, tillage costs for the dryland and irrigated treatments were assumed to be $49.40 and $74.25 ha-1, respectively, and fertilizer costs for the dryland and 150- and 300-mm irrigation treatments were $64.52, $102.55, and $117.37 ha-1, respectively. Land costs were not included. Pumping costs (based on natural gas) of $0.12, $0.20, and $0.28 mm-1 irrigation water and corn prices of $0.079, $0.099, and 0.119 kg-1 were assumed.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Growing season rain was above average in 1998 and 1999 but well below average in 2000. All years had adequate rain for stand establishment and early growth. The driest months were September 1998 and 2000, but as with temperature, September rain was less important than rainfall in the other months. On a practical basis, June 1998, June 2000, and August 2000 had the least rain—22, 17, and 24 mm, respectively. Rain was 83 mm below average in 2000, with only July having above-average rain. However, the 123 mm in July 2000 was the second highest monthly rain of the 3-yr period, exceeded only by 160 mm in July 1998. Individual rain events in June 2000 did not exceed 10 mm (data not shown). The last effective rain of the 2000 growing season, 20 mm, occurred on 9 and 10 August. Only 9 mm of rain occurred between 8 June and 2 July 1998, and only 7 mm occurred between 10 June and 4 July 2000.
Explanation of Means Comparison
Means for soil water, yield, and WUE are presented in Tables 2 through 4. All means are listed. Individual means were separated by the LSD only when there was a three-way interaction, as for 1999 in Table 3. Means (averages) for two-way interactions were separated when such interactions occurred. Such means were not listed if there was no interaction. As an example, refer to the 1998 and 2000 data in Table 3. There were hybrid x population (averaged across irrigation) interactions in both years. Means to be compared in both years are population comparisons within the same hybrid, averaged across irrigations, and hybrid comparisons within the same population, also averaged across irrigations (comparisons could be made at different populations also). There was a hybrid x irrigation interaction (averaged across populations) in 1998 but not in 2000. Thus, irrigation means for each hybrid (third and sixth rows in Table 3), averaged across population, are separated in 1998 but are not listed in 2000. There were irrigation x population interactions (averaged across hybrids) in both years. All this means is that in 1998, H2 responded significantly to each irrigation (sixth row) while H1 responded significantly to only one irrigation (third row). The irrigation x population interaction indicates that the average response was greater at P2 than at P1. In 2000, the absence of the hybrid x irrigation interaction indicates that the responses of both hybrids within a population were similar. Therefore, only the irrigation x population interaction was used for irrigation comparisons in 2000.
Means are separated by lower- and uppercase letters where convenient. Numerical LSDs are presented if the means cannot clearly be separated with letters.
Grain Yield
Dryland grain yields ranged from 3.59 Mg ha-1 for H2 at P2 in 2000 to 8.65 Mg ha-1 for H2 at P1 in 1998 (Table 2). Irrigated yields ranged from 7.09 Mg ha-1 for H1 at P1 with one irrigation in 1999 to 12.09 Mg ha-1 for H2 at P2 with two irrigations in 1998.
Three-way interactions occurred in 1999. For H1 at P1, grain yield did not differ significantly between dryland and two irrigations, but one irrigation yielded 7.09 vs. 5.72 Mg ha-1 for the dryland treatment. For H1 at P2, both irrigation treatments resulted in more grain yield than the dryland treatment, but there was no difference between one and two irrigations. At H2, the differences between one and two irrigations at either population were not significant and both yielded more grain than the dryland treatment. The lack of response of two irrigations over that of one was probably due to rain. Corn was irrigated at V7 on 18 June 1999, and 70 mm of rain occurred during a 4-d period beginning on 22 June, reducing the probability of a response to a second irrigation. Above-average rain in May and early June also reduced the response.
The high population yielded more grain than did the low population at all treatment levels of H1 in 1999. The high population increased grain yield from one and two irrigations but reduced yields of the dryland treatment of H2. When comparing hybrids at the same irrigation and population, the P1 yield of H2 was significantly higher than that of H1 only with two irrigations (8.69 vs. 6.47 Mg ha-1). The dryland P2 yield of H2 was significantly lower than that of H1 (4.52 vs. 6.58 Mg ha-1) while the P2 yield of H2 was greater than that of H1 with two irrigations (9.95 vs. 8.15 Mg ha-1). The difference between hybrids at P2 with one irrigation was not significant.
Thus, in 1999, two irrigations of either hybrid did not increase grain yield significantly above that of one irrigation. There was no hybrid difference when irrigated once. However, H2 yielded significantly more than H1 with two irrigations. For a producer who could only irrigate one time, there was no advantage to a later hybrid.
There were no three-way interactions in 1998 and 2000. Averaged across irrigations, the later hybrid yielded more than H1 at both populations in 1998. The hybrid x population interaction occurred in 1998 because the increase in grain yield due to population was greater for H1 (9.64 vs. 8.09 Mg ha-1) than for H2 (10.37 vs. 9.89 Mg ha-1). Hybrid differences were greater for P1 (9.89 vs. 8.09 Mg ha-1) than for P2 (10.37 vs. 9.64 Mg ha-1). The later hybrid responded more to irrigation than did H1. Averaged across populations, the grain yield increase of H2 with one irrigation was 2.32 Mg ha-1 (28%) while the grain yield increase of H1 with one irrigation was 1.16 Mg ha-1 (15%). Grain yield of H2 increased significantly at both irrigation levels, but grain yield of H1 increased significantly only at the first irrigation level.
The irrigation x population interaction in 1998 was partially due to no grain yield difference for population with no irrigation (8.24 vs. 8.04 Mg ha-1) while the significant increase due to population was greater with two irrigations than with one. Within population, there was a larger increase in grain yield with irrigation at P2 than at P1. The difference between zero and two irrigations at P2 was 3.18 Mg ha-1 (39%) while at P1 it was 1.50 Mg ha-1 (19%). There was no significant difference in the grain yield of one and two irrigations at P1, but two irrigations yielded 1.06 Mg ha-1 (10%) more than one at P2.
The year 1998 can be summarized by saying that a producer would have obtained the highest grain yield by irrigating H2 twice. The high population produced more yield than P1.
Results were different in 2000 because of less growing season rain. Due to the dry conditions, H1 yielded more than H2. Although yields were similar for both hybrids at P1 (7.17 vs. 7.05 Mg ha-1), at P2, H1 yielded an average of 1.24 Mg ha-1 (19%) more than H2 (7.87 vs. 6.63 Mg ha-1). Because of the dry weather, each population responded to each irrigation. In 1998, only P2 responded to the vegetative irrigation; neither hybrid responded to the vegetation irrigation in 1999. The irrigation x population interaction indicates that, in 2000, the increases in grain yield from one irrigation to two were 0.89 Mg ha-1 (11%) for P1 and 1.26 Mg ha-1 (16%) for P2. Corresponding increases from one irrigation vs. dryland were 61 and 87% for P1 and P2, respectively. Thus, the biggest grain yield increase came from one irrigation, as expected. The dryland treatment resulted in more grain yield at P1, whereas with one irrigation, population had no significant effect on grain yield and with two irrigations, P2 yielded more.
Averaged across years (1998–2000), H2 yielded 0.82 Mg ha-1 more than H1 at P1 (8.05 vs. 7.23 Mg ha-1), but there was no significant difference at P2. Both hybrids yielded more with one irrigation than the dryland treatment, but two irrigations did not significantly increase grain yield of either hybrid. However, the irrigation x population interaction (averaged across hybrids) indicates that at P2, two irrigations yielded 0.89 Mg ha-1 more than one irrigation. This indicates that plant population needs to be higher for two irrigations than for one. However, this does not mean that population has to be lower if a producer can only irrigate once because P2 never yielded less than P1, even with one irrigation.
To summarize, the average grain yield of the irrigated treatments during the 3 yr was 8.51 Mg ha-1 for H1 and 9.40 Mg ha-1 for H2. Thus, irrigated H2 yields averaged 0.89 Mg ha-1 (10%) more than H1 yields. The high population yielded more than did P1 with both irrigations, but population had no effect on dryland grain yield.
Soil Water Depletion and Water Use
Soil water remaining in the soil profiles at corn harvest is presented in Table 3, and water use by the crop is presented in Table 4. The water-holding capacity of Ulysses silt loam is approximately 630 mm of water in a 1.8-m profile; about 300 mm is unavailable. There was considerable water remaining in the profiles in 1998 and 1999, partially because of rain late in the growing season. Because of lower growing season rain (Table 1), soil water was essentially depleted in 2000, especially by H2. The 116-d hybrid removed the most water from the profile in 1998 and 1999 also. There were 54, 42, and 29 mm less water in the H2 than H1 profiles in 1998, 1999, and 2000, respectively. There were irrigation x population interactions in 1998 and 2000. In 1998, there was more water remaining in the profiles of the irrigated than dryland treatments at both populations, but the amounts did not differ between one and two irrigations. The high population removed more water from the two irrigated treatments, but water extracted by dryland treatment was not affected by population. In 2000, the amount of water remaining in the P2 profile increased with the amount of water applied. Extraction by P1 was similar to that in 1998 in that there was more water remaining in the irrigated treatments than in the dryland treatment, but the irrigated treatments did not differ from each other. The high population removed more water than P1 from dryland and one irrigation, but P1 removed more water from the two-irrigation profile. However, the amount was only 7 mm more than that removed by P2; thus, there was no practical significance. There was no irrigation x population interaction in 1999, and P2 removed an average of 20 more water than did P1. The amount of water remaining in the profiles increased with irrigation.
The amount of water used (Table 4) is directly related to the amount of water remaining in the soil profiles; thus, a complete discussion of water use would bring out many of the same points as in the soil water depletion discussion above. To summarize, water use was greater in the first 2 yr of the study because of more rain (Table 1). Water use was affected by both hybrid and population, but the hybrid effect was greater. The 116-d hybrid used 40 mm more water (averaged across irrigations) than H1 in 1998 and 1999 but only 21 mm more in 2000. The higher population used an average of 20 mm more water (averaged across irrigations) in 1999. The three-way interactions in 1998 and 2000 indicate that differences in water use between populations, although usually statistically significant, were small. Population had the least effect on water use in 2000 because the profile was nearly depleted by P1; thus, there was little additional water to be used by P2.
Water Use Efficiency
Overall WUE is presented in Table 5. A hybrid x population interaction in 1998 occurred because P2 resulted in a higher WUE for H1 but not H2. The H1 WUE at P2 and both H2 WUEs were essentially the same. An irrigation x population interaction occurred because the P2 WUE was higher than that of P1 with one and two irrigations, but the dryland WUEs were similar. Also, the WUEs at either population did not differ significantly between dryland and one irrigation, meaning the increase in yield was proportional to the combination of rain and irrigation water. The dryland and one-irrigation WUEs from both populations exceeded the WUEs of two irrigations. This was not unexpected because one irrigation produced a larger grain yield increase than did two irrigations (Table 3); thus, the WUE resulting from two irrigations was lower.
As with grain yield, WUE exhibited three-way interactions in 1999. Two irrigations resulted in the lowest WUE of H1 because of the lack of grain yield response to two irrigations over that of one (Table 2). Dryland resulted in the lowest WUE of H2 because of low dryland grain yields, particularly from P2. With the exception of dryland H2, the WUEs of both hybrids increased at P2. With irrigation and the same population, the WUE of H2 was significantly higher than that of H1 only with two irrigations at P1 (11.1 vs. 8.7 Mg ha-1). With dryland, the WUEs of H1 were higher at both populations.
In 2000, the WUE of H1 (averaged across irrigations) was higher than that of H2 at both populations. The WUE of H1 was increased by P2 while the WUE of H2 was decreased by P2. This differs from 1998 and 1999 because in those 2 yr, P2 of both hybrids either increased irrigated WUE or had no effect. However, WUE of H2 at P2 was lower mostly because of a lower dryland WUE. The WUE of P2 with one irrigation was slightly lower than that of P1, and the WUEs of P1 and P2 did not differ with two irrigations.
The irrigation x population interaction in 2000 was partially caused by a lower dryland WUE at P2 than at P1 but a higher WUE at P2 with two irrigations. The higher WUE at P2 with two irrigations was due to H1 at P2 yielding more grain than H2 at P2 (compare 10.09 with 8.59 Mg ha-1 for the hybrids with two irrigations in Table 3). At P1, the highest WUE was attained with one irrigation, and there was no significant difference between dryland and two irrigations. The highest WUE at P2 also resulted from one irrigation, but the dryland WUE was significantly lower than that from both one and two irrigations.
The WUE values in Table 5 were calculated using both rain and irrigation. The IWUE values in Table 6 were due only to irrigation. There was a three-way interaction for IWUE in 1999, as with yield and overall WUE, but no interactions occurred in 1998 and 2000. Thus, IWUEs in 1998 and 2000 will be discussed together. Irrigation water use efficiencies were higher in 2000 than in 1998 because less rainfall resulted in a larger response to irrigation. As expected, the largest IWUE resulted from the tassel irrigation, which was about three times the IWUE resulting from the vegetative irrigation in both years. Irrigation water use efficiencies were unaffected by hybrid in 1998 and 2000. The IWUE resulting from P2 was about twice as high as that from P1 in 1998 and 30% higher in 2000.
The IWUE from one irrigation was also highest in 1999. The early hybrid had essentially no response to the vegetative irrigation (2 vs. 1) and, in fact, was negative at the low population due to lack of a grain yield response (Table 2). The IWUE with one irrigation of H2 at P2 was 72% higher than that of H2 at P1 (31.9 vs. 18.5) but resulted mostly from the yield reduction of dryland H2 at P2 (Table 3).
Grain Yield Components
Coefficients of determination (R2) for yield vs. the yield components ears ha-1, kernels ear-1, and kernel weight are given in Table 7. Data are pooled across years because there weren't enough data points to compute accurate R2 values for individual years. Yield component data for individual years is discussed in more detail below. Coefficients of determination were computed for each hybrid at each population and for both hybrids at each population. This minimizes the effect of ears ha-1 because ears ha-1 is mainly determined by plant population. The corn from each hybrid averaged one ear per plant, plus or minus a few hundredths of an ear (data not shown), except for H2 in 2000. At the high population with no irrigation, H2 produced 0.90 ear plant-1 in 2000. For this reason, and because the corn was not thinned to exact populations, ears ha-1 still had a minor influence on R2.
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The hybrid x irrigation (averaged across population), hybrid x population (averaged across irrigation), and irrigation x population (averaged across hybrid) interactions for kernels ear-1 and kernel weight are presented in Fig. 1 through 3 , respectively. Kernels ear-1 and kernel weight usually increased with irrigation (Fig. 1). The data from 1998 and 1999 indicated a greater response to irrigation of H2 compared with H1. Although the responses of kernels ear-1 to irrigation of both hybrids were similar in 1998, the kernel weight of H2 responded more to irrigation, or at least to one irrigation, than that of H1. In 1999, the kernel weight of H2 was increased by both irrigations, and kernel weight of H1 was increased by one irrigation. There were no significant hybrid differences. Irrigation resulted in a larger increase in kernels ear-1 for H2 than H1 in 1999. With no irrigation, H2 had more than 100 fewer kernels ear-1 than did H1 while with two irrigations, H2 had almost 100 more. This is reflected in the grain yield increase of H2 due to irrigation, particularly at P2 (Table 3). The final year of the study had more climatic stress than the other years. Differences in kernels ear-1 between the two hybrids were not as great as in 1999, but H1 produced more kernels ear-1 than did H2 with zero and two irrigations. The effects of stress are most obvious in kernel weight. Although there was no difference between hybrids in kernel weight, average kernel weight in 2000 was 4.0 g lower than in 1999 and 5.4 g lower than in 1998.
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Kernels ear-1 and kernel weight of P2 were always significantly lower than those of P1 at the same irrigation level (Fig. 3). Except for P1 kernels ear-1 in 1998 and P2 kernel weight in 1999, kernels ear-1 and kernel weight increased significantly with one irrigation in all years at both populations. In 1999 and 2000, there was no significant increase in kernels ear-1 at either population from one to two irrigations. In 1999, there was no significant increase in kernel weight from one to two irrigations at either population or from dryland to one irrigation at P2.
Economics
An economic analysis using the 3-yr average is illustrated in Fig. 4
. The top part of Fig. 4 consists of returns of the two hybrids at a corn price of $0.099 kg-1 and pumping costs of $0.12, $0.20, and $0.28 mm-1. The lower part of Fig. 4 consists of returns at a pumping cost of $0.20 mm-1 and corn prices of $0.079, $0.099, and $0.119 kg-1. Return for H1 at a corn price of $0.099 kg-1 (Fig. 4a) indicates that the returns for both irrigation levels are greater than for dryland at the $0.12 mm-1 pumping cost but do not differ from each other. At $0.20 mm-1, returns from 150 mm are greater than from dryland, but the 350-mm return is the same as with dryland. At the $0.28 mm-1 pumping cost, the return from 150 mm is the same as dryland, and the return from 300 mm is $61 ha-1 less than that of dryland. Returns from H2 at a corn price of $0.099 kg-1 (Fig. 4b) follow the same pattern as H1 except that irrigated returns are $45 to $50 ha-1 higher. With H2 and the $0.28 mm-1 pumping cost, the return from 150 mm was $41 ha-1 more than that of dryland, but 300 mm returned $11 ha-1 less than dryland.
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The data indicated that returns from 300 mm of irrigation water were never more profitable than from 150 mm, regardless of hybrid maturity. The 150-mm return from H1 exceeded the dryland return when pumping costs were $0.20 mm-1 or less and the corn price was $0.099 kg-1 or higher. With H2 at the $0.079 kg-1 corn price and $0.20 mm-1 pumping cost, the return from 150 mm of water was barely more than that of dryland (Fig. 4d). Of course, the return from 300 mm (or 150 mm) increases as the corn price increases. At a $0.119 kg-1 corn price and $0.12 mm-1 pumping cost, the 300-mm return from H2 was $25 ha-1 higher than the 150-mm return (data not shown). However, that difference was eliminated at a pumping cost of $0.20 mm-1.
Under the conditions of this study, risk-averse producers may not want to apply more than 150 mm of water unless corn prices exceed $0.099 kg-1 and pumping costs are less than $0.20 mm-1. At the $0.20 mm-1 pumping cost, irrigating short-season corn once would return $27 ha-1 more than dryland production at a corn price of $0.099 kg-1 (Fig. 4c), and irrigating long-season corn once would return $71 ha-1 more (Fig. 4d). This is enough return to prevent a return to dryland. However, if the corn price drops to $0.079 kg-1, the short-season hybrid results in a loss of $26 ha-1, and the long-season hybrid returns only $8 ha-1 more than dryland production.
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SUMMARY |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARYREFERENCES |
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Returns of irrigated corn depend on corn price and pumping costs, two things over which the farmer has no control. At relatively high corn prices and relatively low pumping costs, using more irrigation water increases profits. The direction of crop prices is unknown. However, pumping costs are not expected to drop to the costs of 2 or 3 yr ago. Under the climatic conditions of this study, and at current pumping costs of about $0.20 mm-1, farmers growing limited flood-irrigated corn probably cannot afford to irrigate more than one time unless the corn price exceeds $0.099 kg-1. These results indicated that a farmer flood-irrigating corn one time and receiving $0.099 kg-1 will make $27 ha-1 more with a short-season hybrid and $71 ha-1 more with a long-season hybrid compared with dryland production. At current pumping costs, a single irrigation is profitable enough to prevent a return to dryland systems. However, in recent years, corn prices have usually been below $0.099 kg-1 and have even remained below $0.079 kg-1 for long periods of time. Thus, corn prices have to increase and pumping costs decline, or at least not increase any more, to prevent the conversion of irrigated corn hectares to dryland.
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NOTES |
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1 Mention of a trade name does not imply endorsement by Kansas State University over comparable products. 
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