Rotation effect on sorghum response to nitrogen fertilizer under different rainfall and temperature environments.

摘要

Cropping sequence effects on sorghum response to nitrogen fertilizer under different rainfall and temperature regimes were evaluated in eastern Nebraska. The Standardized Precipitation Index (SPI) and temperature Z-scores were used to characterize the 18-year cropping period into eight sets of contrasting cropping environments. Mean sorghum yields ranged from 4050 to 6260 kg/ha in continuous cropping, and from 5130 to 7120 kg/ha in rotation with soyabeans, a significant increase with crop rotation.Yields were lower in dry years with hot April temperatures than in dry years with cool April temperatures. Hot April temperatures improved yields in wet years. April temperature did not affect yield if a wet pre-season was followed by a dry cropping season. Sorghum responded more to fertilizer N in dry than in wet years, reflecting less available N from soyabeans and the soil nutrient complex in the previous year. Sorghum grown in rotation with soyabeans did not generally respond to fertilizer N, suggesting that high fertilizer N rates are unnecessary in rotation systems. Low September temperatures reduced final yields. Given the high probability of confronting adverse cropping conditions, it is strongly recommended that sorghum be considered as an important component of rainfed cropping systems in eastern Nebraska to ensure minimum crop loss to farmers. Greater economic gains can be achieved by using rotations with soyabeans because of higher sorghum yields and lower fertilizer costs, and these aremost likely under the favourable rainfall and temperature regimes identified in this study.