DOUBLE CROPPING WINTER RAPESEED AND GRAIN SORGHUM

Since rainfall generally exceeds 500 mm during the winter months and soil erosion is a problem in the southern U.S.A., a cover crop is essential to reduce soil losses. Continuous cultivation of a crop on the same land also provides the opportunity for pest problems to develop. A winter rapeseed (Brassica napus L.)-grain sorghum (Sorghum bicolor (L). Moench.) double-cropping system was investigated in the field from 1981 to 1984. Conventional tillage (CT) and no-till (NT) systems were used for both crops. Gullivar rape was planted in October and harvested in June. Winter rapeseed yields averaged 2.87 t ha−1 on CT plots in 1982. Averaged over 1983 and 1984, rape yields were 1.66 and 0.73 t ha−1 on CT and NT plots, respectively. However, the seeding method biased the rapeseed performance. Problems were encountered with winter weed control and pod shattering in the winter rape plots. Two sorghum hybrids, R. C. Young Oro Txtra and Funks G-550, were planted in June and harvested in October. Grain yields were not significantly different between hybrids (Oro 5.69 t ha−1, Funk 5.67 t ha−1) or between tillage systems (CT 5.59 t ha−1, NT 5.78 t ha−1). Grain yield differences were noted for year × hybrid × tillage interactions. Rape was a weed problem in the sorghum plots. The winter rape-sorghum double-cropping system offers an alternative to current winter small grains-sorghum/soybean (Glycine max (L.) Merr.) or winter annual legume-sorghum/soybean (Glycine max (L.) Merr.) systems; however, markets for the winter rapeseed and production economic analyses are needed prior to adoption of the system. Additional winter rapeseed research is needed to evaluate yields properly under NT conditions.Key words: Sorghum bicolor (L.) Moench, Brassica napus L., conservation tillage, multiple cropping, sorghum, rapeseed