TILLAGE, PLANTING DATE, AND PLANT-POPULATION EFFECTS ON DRYLAND CORN

Dryland corn (Zea mays L.) usually is not grown in western Kansas beca use of its low yield potential under drought stress. A study was condu cted at the Southwest Research-Extension Center near Garden City, KS, from 1991 through 1994 to determine proper management practices for dr yland corn. Corn was planted in a wheat (Triticum aestivum L.)-corn-fa llow rotation in early (D1), mid (D2), and late (D3) May at plant popu lations of 12 000 (P1), 18 000 (P2), and 24 000 (P3) plants/acre with conventional tillage (CT) and no tillage (NT). No tillage increased yi elds 100% in the driest year (1991), increased yields by 41% in 1994, and resulted in yield increases in most comparisons in the remaining y ears. The highest yields in the dry year of 1991 resulted from D1 and D3, whereas D1 and D2 usually produced the highest yields in all other years. In 1991, yields declined with increased plant population, but the average yield reduction of 16% for P3 with NT was half that with C T. In other years, yields usually increased with an increase in popula tion. In 1992 and 1993, P3 resulted in average yield increases,over P1 of 41% and 28% with NT and CT, respectively. In 1994, NT usually prod uced the most grain with P2, whereas population increases did not incr ease CT yields. We conclude that dryland corn in southwest Kansas shou ld be planted in early to mid-May at plant populations not exceeding 1 8 000 plants/acre. No tillage is essential for adequate yields in dry years and will usually result in yield increases in years with more fa vorable climatic conditions.