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Importance of Soil and Cropping Systems in the Development of Regional Water Quality Policies

Dep. of Agronomy, Oklahoma State Univ., Stillwater, OK 74078,
Dep. of Agric. Eng., Oklahoma State Univ., Stillwater, OK 74078,
Dep. of Agric. Econ. Oklahoma State Univ., Stillwater, OK 74078.

^* Corresponding author.

ABSTRACT

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.

Approved as Journal Article no. 6392 of the Oklahoma Agric. Exp. Stn. Research Supported by the U.S. Geological Survey, Dep. of the Interior, under USGS award 14-08-0001-G1750. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of Oklahoma State Univ. or the U.S. government.

Received for publication January 12, 1993.

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