Sunflower response to tillage and nitrogen fertilization under intensive cropping in a wheat rotation

Sunflower (Helianthus annuus L.) is a warm-season, intermediate water-use c rop that can add diversity to dryland crop rotations, Reduced tillage syste ms may Enhance sunflower yield in intensive cropping systems. A 12-year stu dy was conducted to determine how sunflower er cultivars of early and mediu m maturity respond to tillage system (conventional-till, CT; minimum-till, MT; no-till, NT) and N fertilization (34, 67, and 101 kg N ha(-1)) within a dryland spring wheat (Triticum aestivum L.)-winter wheat-sunflower rotatio n. Averaged across N rates, cultivars, and years, sunflower seed yields wer e greater with MT (1550 kg ha(-1)) than with NT (1460 kg ha(-1)) and CT (14 50 kg ha(-1)). Increasing N rate above 34 kg N ha-L generally increased gai n yield, but varied from year to year. The tillage X N interaction showed t hat the highest seed yields were obtained with NT (1638 kg ha(-1)) and MT ( 1614 kg ha(-1)) at 101 kg N ha(-1). Total plant-available water (TPAW) of < 350 mm greatly reduced sunflower yield potential, due to water stress, comp ared with yields for 350 to 500 mm of TPAW. TPAW > 500 mm did not result in increased sunflower yields over those with 350 to 500 mm TPAW. Yield diffe rences between cultivar maturity classes varied from year to gear and with tillage and N level. At the lowest N rate, weeds were more problematic in N T than in CT and MT plots. More N fertilizer may be needed with NT to optim ize sunflower yields than with CT and MT, because of less residual soil NO3 -N with NT. Results indicate that producers in the northern Great Plains ca n use sunflower successfully in annual a cropping systems, particularly if MT and NT are used with adequate N fertilization.