Abstract
Maize (Zea mays L.), sorghum (Sorghum bicolor Moench) and Italian ryegrass (Lolium multiflorum Lam., IR) are major forage crops in southern Kyushu. This study tested 3 cropping systems typical to the region (double cropping of maize and IR (M-IR), double cropping of sorghum and IR (S-IR), and double cropping of maize (M-M)) for 5 years for their performance on the non-fertile, poorly permeable heavy soil. A single cropping of maize on fertile, permeable Andosol (M) was also tested for comparison. Herbage dry matter yields of summer crops (maize and sorghum) were more variable among years (CV=46.0-54.4%) than those of IR as a winter crop (CV=9.5-23.1%), with the low yields being associated with frequent attacks of typhoons and heavy rainfalls. Consequently, in M-IR and S-IR, incorporation of IR into the cropping system decreased the year-to-year variability in herbage yield (31.2 and 48.3%, respectively). Maize on Andosol (M) showed 2-34% higher yields than the 1st-crop maize on the heavy soil (M-M). The results confirm the relatively low productivity of the heavy soil and show the advantage of combining a winter crop with a summer crop for stabilizing annual herbage production on the heavy soil in southern Kyushu.
