Rainfall and previous crop effects on crop yields
Afield study was conducted between 1972 and 1982 to compare the effects of previous crop on row crop yields under rainfed conditions in eastern Nebraska. The objectives were to determine the effects of fallow and three previous crops: corn (Lea. maysLJ, soybeans /Glycine max (L.) Mem], and grain sorghum /Sorghum bicolor (L.) Moench], on the growth and grain yield of the same crops. The study was conducted on a Sharpsburg silty clay loam (fine, montmorillonitic, mesicf Typic Argiudoll). Corn grain yield was most variable (C. V. 23.4percent) compared to soybean (C. V. 13.6percent) or grain sorghum (C. V. 9.5 percent) yields. Corn was also the most sensitive crop to previous crop effects. The range of treatment yields for each crop was 47 percent, 22 percent, and 11 percent of the overall means for corn, soybean, and sorghum, respectively. Previous crop affected yields for all crops, but the effects were not consistent across years. All crops produced highest yield following fallow. Yields of corn, soybean, and grain sorghum following fallow were 74, 25, and 10 percent higher than their respective monoculture yields. In years of average precipitation, a corn-soybean sequence produced the greatest yield. In years having above- or below-normal precipitation, a grain sorghum-soybean sequence produced the highest yield.
Rotation effect on sorghum response to nitrogen fertilizer under different rainfall and temperature environments
Cropping sequence effects on sorghum (Sorghum bicolor L. Moench) 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-yr 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 soybean (Glycine max), 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 soybean and the soil nutrient complex in the previous year. Sorghum grown in rotation with soybean 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 soybean because of higher sorghum yields and lower fertilizer costs, and these are most likely under the favorable rainfall and temperature regimes identified in this study. The results provide useful information for fine-tuning management options to maximize sorghum yields and reduce input costs in atypical years.
What is Enlightenment
Enlightenment is man's emergence from his self-imposed nonage. Nonage is the inability to use one's own understanding without another's guidance. This nonage is self-imposed if its cause lies not in lack of understanding but in indecision and lack of courage to use one's own mind without another's guidance. Dare to know! (Sapere aude.) "Have the courage to use your own understanding," is therefore the motto of the enlightenment.