Declining groundwater levels in irrigated areas of the Great Plains may require a shift to limited irrigation or a return to dryland production. A field study was developed to determine the yields that could be attained in minimum till cropping systems that included winter wheat (Triticum aestivum L.), corn (Zea mays L.), soybean [Glycine max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench] under dryland farming, and limited and full irrigation. The limited irrigation allocation was 6 in./crop/year. The experiment began in 1981 on a Cozad silt loam (fine‐silty, mixed, mesic Fluventic Haplustoll) at North Platte, NE, where average annual precipitation was 19.4 in. Management practices for fertilizer, herbicide, variety selection, and pest management were modified as improved varieties, technology, and products became available. In the winter wheat (WW)‐corn (C)‐soybean (SB) rotation, 6‐yr average yields for winter wheat were 33, 64, and 65 bu/acre for dryland, limited, and full irrigation, respectively. Average corn yields were 90,161, and 188 bu/acre for the three moisture regimes, whereas soybean average yields were 29, 52, and 59 bu/acre. The limited irrigation yields were 99, 86, and 88% of fully irrigated yields for winter wheat, corn, and soybean. Marginal returns from limited irrigation were 10.9 bu/in. for corn, 4.3 bu/in. for soybean, and 5.9 bu/in. for winter wheat. Poor stand establishment in heavy residue and chlorosis were problems in grain sorghum culture, which may limit its competitiveness with corn in this area. This research demonstrated that minimum tillage cropping systems and limited irrigation have possibilities for maintaining acceptable yield levels of corn, winter wheat, and soybean in areas of declining irrigation water. Research Question Declining groundwater levels in irrigated areas of the Great Plains may require a shift to limited irrigation or a return to dryland crop production. Advances in dryland agriculture through the use of herbicide, residue management, and no‐till farming have improved dryland grain yield stability. Dryland grain yields and profitability are lower and not as stable as those with irrigated agriculture. Crop production data are needed to assist in decisionmaking in regions that may experience a transition from full irrigation to limited irrigation or dryland agriculture. The techniques of moisture conservation required for successful dryland farming plus the appropriate timing of limited irrigation must be researched to determine the production potential of different cropping systems. Such systems might extend aquifer life and provide smoother transition from intensive irrigation to dryland or limited irrigation in the central Great Plains. The primary objective of this study was to determine the yields that could be attained with the application of limited irrigation in minimum tillage cropping systems with four crops common to the Great Plains: winter wheat, corn, grain sorghum, and soybean. Literature Summary Numerous studies throughout the Great...
Careful management of both N fertilizer and irrigation water is required to minimize NO−3 leaching below the root zone in irrigated corn (Zea mays L.) production. Practices related to management of fertilizer N and irrigation water were evaluated in a series of studies conducted at 79 sites in Nebraska, from 1984 through 1988. Practices evaluated included N credit from NO−3 in soil, N credit from NO−3 in irrigation water, realistic yield goal selection, and irrigation scheduling according to crop water use. Nitrogen was applied in field length strips at the recommended rate, and at rates 50 lb N/acre above and below the recommended rate. Groundwater NO−3‐N concentrations at sites ranged from 0.5 to 46.1 ppm. The procedure for determining the recommended fertilizer N rate provided adequate N without reducing yields. Averaged over 79 sites, yield goal was 170 bu/acre; recommended fertilizer N rate was 130 lb/acre; yield was 173 bu/acre; and fertilizer N reduction due to accounting was 45 lb N/acre. Because of the often high NO−3‐N concentrations in irrigation water and substantial amounts of NO5 in soil (ranging from 15–265 lb/acre in 4 ft), grain yield was relatively insensitive to fertilizer N rate. With average values for soil and irrigation water N credits, increasing the fertilizer N rate by 100 lb/acre increased yield by only 1.3%. Decreasing the fertilizer N rate by 50 lb/acre decreased yield by only 2.6%. At the three primary N rates used in these studies (−50, 0, and 50 deviation from the recommended rate), irrigation water NO−3‐N concentration, irrigation water amount, and soil NO−3 level all influenced yield more than fertilizer N rate.
A gronomy J our n al • Volu me 10 0 , I s sue 4 • 2 0 0 8 ABSTRACT Water levels in the Ogallala aquifer are declining, and with the resultant decrease in water capacity of wells, irrigators face diffi culty in meeting crop water needs. Off -season irrigation is common in the region, although research has shown it is oft en ineffi cient. Storage effi ciency of off -season irrigation is aff ected primarily by the amount of water in the soil profi le during storage. Because of much interest in off -season irrigation, our objective was to describe the relationship between water storage effi ciency and soil profi le water content. Th rough use of simulation results from a water balance model, we calculated net water gain on 15 May that resulted from fall or spring irrigation. Storage effi ciency was related with the maximum of soil water (SW) from irrigation to 15 May. Storage effi ciency was 90 to 95% of spring, or 80 to 85% of fall net irrigation amount, with SW in the lower half of the available water (AW) zone. As SW increased above ≈55% AW for fall or ≈60% AW for spring irrigation, storage effi ciency decreased and approached zero with SW near 100% AW. Th is analysis will help producers understand water storage effi ciency of off -season irrigation and how storage varies with SW.
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