The economic impact of timing of grazing termination in the wheat (Triticum aestivum L.) grain‐stocker cattle (Bos sp.) enterprise has not been elucidated. A 4‐yr study used the first hollow stem stage of growth in ungrazed wheat as a grazing termination indicator and the subsequent effect on net return. First hollow stem is the stage at which hollow stem can first be identified above the crown; it occurs prior to the growing point reaching the soil surface. Net return was maximized when grazing was terminated at first hollow stem. Grain yield decreased (P< 0.05) 83 kg ha−1 d−1 as cattle grazed past first hollow stem. Increased weight gain by cattle was not sufficient to offset grain yield losses. Since hollow stem formation was delayed in grazed wheat, producers who use semidwarf wheat as a dual‐purpose crop should monitor the morphological stage in ungrazed areas of the field to determine the optimum time to terminate grazing.
Potential economic and environmental effects of broad versus targeted nitrogen use policies are evaluated in five Central High Plains subregions. Results indicate that per-acre restrictions are more effective than total nitrogen restrictions in reducing expected nitrogen losses in runoff and percolation, and reducing percolation losses at all probability levels. Because of the distribution of soils within subregions, targeting nitrogen reductions to more permeable soils may not produce the anticipated reductions in percolation. It may be more effective to target nitrogen restrictions on production systems than on soil types. Reductions in producer income are less for targeted than for broad policies.Agricultural chemicals and fertilizers have been cited as significant groundwater contaminants (Office of Technology Assessment). EPA reported that over seventy pesticides were detected in the groundwater of thirty-eight states, and forty-six pesticides found in groundwater in twenty-six states were from agricultural use (Office of Technology Assessment). Nitrates are the most commonly detected agricultural chemicals in groundwater. EPA estimated that more than half of the nation's wells contain nitrates, with about 1.2% of the community wells and 2.4% of the rural wells having concentrations above
Targeting certain soils and cropping systems may be necessary in consideration of regional water quality protection policies. However, little information is available relating soils and cropping practices to regional water quality problems. This study evaluates crop yield and NO3‐N movement to surface and groundwater on four soils and nine principal cropping systems in the High Plains region of Oklahoma. The cropping systems involve wheat (Triticum aestivum L.), grain sorghum [Sorghum bicolor (L.) Moench], and corn (Zea mays L.), and are part of a regional data base also containing soils and chemical management information. For each combination of crop, soil, cropping system, and chemical alternative, a 20‐yr simulation was made. The simulation was based on a modeling system that includes EPIC‐PST (crop growth/chemical movement model) interfaced with a Geographic Information System (GIS), Earthone. Results of each simulation included crop yield and NO3‐N movement in runoff and percolation. Results show wide variations in NO3‐N losses for different soils, irrigation systems, and cropping systems. When compared with continuous irrigated wheat and grain sorghum cropping systems, double‐cropped wheat‐grain sorghum resulted in greater NO3‐N loss in percolation. Compared with sprinkler and LEPA (low energy precision application) irrigation systems, furrow irrigation resulted in high NO3‐N loss on both fine‐textured and coarse‐textured soils, with significantly greater loss on the coarser‐textured soils. The modeling framework can be used to compare alternative water quality policies. Broad policies such as a restriction on the amount of N that can be applied per hectare can be compared with targeted policies, such as limiting N applications or irrigation water use on coarser soils or under furrow irrigation.
A farm‐level risk programming framework is presented which evaluates income/ environmental risk tradeoffs. This framework uses a time‐series of environmental risk indices to incorporate the stochastic, multiattribute characteristics of environmental outcomes associated with agricultural production practices. The model is applied to a representative farm in the Oklahoma Panhandle region of the Central High Plains. Results indicate that expected income is sensitive to nitrate loading restrictions, and relatively less sensitive to pesticide loading restrictions. Results also indicate that prescriptions derived using deterministic environmental risk measures may ignore significant probabilities of exceeding an environmental standard.
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