DOUBLECROPPING SOYBEAN AFTER CANOLA AND WHEAT

Canola (Brassica napus L.) can be planted as a winter crop and doublec ropped with soybean [Glycine max (L.) Merr.] in the southeastern Coast al Plain of the USA, but Little information is available about canola' s effect on subsequent crops in the rotation. A 2-yr study was conduct ed to determine the effect of deep tillage on both canola and wheat (T riticum aestivum L.), the subsequent response of doublecropped soybean , and response of wheat grown following the soybean crop when controll ed traffic and minimum tillage practices were used. The study was init iated in autumn of 1990 and repeated in 1991 on an Orangeburg loamy sa nd (fine-loamy, siliceous, thermic Typic Paleudults) near Blackville, SC. Canola yields averaged 37.8 bu/acre in 1991 and 43.2 bu/acre in 19 92, whereas wheat yields were 58.0 and 72.5 bu/acre, respectively. In both years, deep tillage (chiseling to 11 in.) had no effect on wheat yields when compared with dishing. Deep tillage increased canola yield s by 12.5% in the drier of the two growing seasons. Soybean yields wer e not significantly affected by the tillage used for the previous crop s. Subsoiled soybean yielded 33.7 vs. 31.9 bu/acre for no-till soybean in 1991, and 22.6 vs. 19.4 bu/acre in 1992. The difference was signif icant (P = 0.05) in 1992, and that year soybean tillage following whea t did not affect soybean yield but following canola, in-row subsoiling resulted in greater soybean yields than no-till. Wheat following soyb ean was not affected by the tillage practice used for the previous win ter crops, and the 1992 wheat yields were unaffected by previous winte r. crop or soybean tillage, In 1993, soybean tillage did not affect su bsequent wheat yield but following canola, in-row subsoiling resulted in greater wheat yields than no-tilt. These results suggest canola has no adverse effect on either soybean or wheat when grown in sequence o n a Coastal Plain soil.