WHEAT TILLAGE AND WATER-QUALITY IN THE SOUTHERN PLAINS

This study considers the impact of conventional-till (moldboard plow o r sweeps) and no-till wheat (Triticum aestivum L.) management practice s on surface and groundwater quality. Concentrations and amounts of se diment, nitrogen (N), and phosphorus (P) in surface runoff, and associ ated nutrient levels in ground water were determined for seven dryland watersheds at two locations for periods up to 14 years. In general, a nnual surface runoff was similar for both tillage practices, ranging f rom 6 to 15 cm. Compared with conventional till, no-till reduced sedim ent, N, and P loss an average of 95%,75%, and 70%, respectively. Concu rrently, elevated levels of dissolved P (maximum 3.1 mg l-1) in surfac e runoff, and nitrate-N in ground water (maximum 26 mg l-1) were obser ved. About 25% more available soil water was in the no-till soil profi les, but this did not translate into increased grain yield. Instead, n o-till grain yields were reduced an average 33% (600 kg ha-1) compared with conventional till, which is attributed to a lower availability o f surface applied fertilizer, and increasing cheat (Bromus tectorum L. ) and associated weed problems. From an overall agronomic and environm ental standpoint, our results indicate that the management of no-till systems should include careful fertilizer placement and timing.