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...

Thirteen hard red winter wheat cultivars were evaluated for their ability to suppress summer annual weeds in grain production systems near North Platte, NE, from 1993 through 1997. ‘Turkey’, a 125-yr-old landrace selection, suppressed both broadleaf and grass weeds more than other cultivars. Some relatively new cultivars, such as ‘Arapahoe’, ‘Jules’, ‘Pronghorn’, and ‘Vista’ suppressed summer annual grasses almost as well as Turkey. Total weed density was negatively correlated with number of winter wheat stems/m2, mature winter wheat height, and lodging. Weed density after wheat harvest was positively correlated with delay in winter wheat seeding date and was negatively correlated with precipitation 0 to 30 d after winter wheat seeding, during tillering, tillering to boot stage, and heading to maturity stage. Mean air temperature 0 to 30 d after wheat seeding was positively correlated with weed density. In the spring, weed density was positively correlated with temperatures during the tillering stage, tillering to boot stage, and heading to maturity stage. Stinkgrass and witchgrass densities were positively correlated with severity of wheat leaf rust. The highest grain-producing cultivars included three medium height cultivars ‘Alliance’, Arapahoe, and ‘Niobrara’. Alliance wheat produced 53% more grain than Turkey, and the other two produced 43% more grain.

SummaryCompetitive ability of 48 sorghum [Sorghum bicolor (L.) Moench] hybrids and 41 parental inbred lines was evaluated using (a) germination percentage and germination rate index, (b) emergence percentage and emergence rate index, (c) seedling vigor, (d) rate of root and shoot development, and (e) cation exchange capacity of roots as selection criteria. Average response of sorghum hybrids was superior to parental inbred lines in all selection criteria. Sorghum lines selected for high and low seedling growth characteristics in laboratory and greenhouse studies showed corresponding competitive advantages over weeds in field studies. Competitive advantage of sorghum over weeds was largely due to rapid germination, emergence, and root and shoot growth during the early stages of sorghum development.

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