Harvested Dry Matter from Single and Double-Cropping Systems

Double-cropping (DC) has been advocated in the United States for increasing feed and food production and production efficiency. We studied single-cropping (SC) and DC systems to determine the most productive crops or crop combinations for harvestable dry matter. Ten crops grown from 1974 to 1976 at Ames in central Iowa were: corn for silage, corn for grain, tropical corn (all Zea mays L.), grain sorghum, forage sorghum, sorghum × Sudangrass (all Sorghum bicolor Moench), pearl millet (Pennisetum americanum (L.) K. Schum), sugarbeets (Beta vulgaris L.), soybeans [Glycine max (L.) Men.], and sunflowers (Helianthus annas L.). These crops were planted alone at recommended times in a SC system and as main (second) crops in DC systems following first crops of winter rye (Secale cereale L.) and spring oats (Avena saliva L.) harvested for forage. Dry matter (DM) yields of oats were greater than for rye. Rye, however, had the advantage of providing soil cover during the winter and being harvested earlier in the spring, thus permitting earlier planting of the main crop. Average DM yields of main crops were greater in the SC system than in the DC system, where the main crop DM yields declined with the later dates of planting. Seme crops (sorghum Average DM yields of main crops were greater in the SC system than in the DC system, where the main crop DM yields declined with the later dates of planting. Some crops (sorghum × sudangrass hybrid, forage sorghum, pearl millet, sunflowers, soybeans) produced comparable yields in the rye-DC and SC systems. Grain yields of grain crops and root yields of sugarbeets declined at a greater rate with later plantings than did whole-crop yields. Corn for grain and corn for silage in the SC system and forage sorghum and sorghum × sudangrass hybrid in both the SC and rye-DC systems produced the highest whole-crop yields. Total DM yields were greater for the early-harvested oat-DC system in 1974 and the rye-DC system in 1975 and 1976 than for other systems. We concluded that there is potential for increased harvestable dry matter by DC in the north central United States, particularly if a small grain harvested early for forage is the first crop of the DC system.