Wednesday, November 7, 2007 - 9:30 AM
262-1
A Retrospective on Crop Rotation Research during the Last Century - What Have We Learned?.
Joseph G. Lauer, University of Wisconsin, Agronomy, 1575 Linden Drive, Madison, WI 53706
Crop rotation is a universal practice used to increase production. Prior to the 1950s, farmers recognized the importance of rotation because few options existed for soil fertility and pest management. During the 1950s and 1960s, rotation effects were hypothesized to be N related; consequently monoculture became popular where chemical fertilizers and pesticides substituted for rotation. During the 1970s, agronomists recognized not all rotation effects could be overcome and that there were N effects and non-N effects thought to be alleopathic with phytotoxic compounds originating from crop residues. During the 1980s, agronomists found that crop rotation improved soil moisture and structure, and beneficial soil microbes increased while pests decreased. During the 1990s, rotation research eliminated factors finding above-ground residue had no effect, and host-specific pathogens did not cause the rotation effect, but root development and grain nutrient composition differences existed. Specific rotation response recommendations were formulated. During the 2000s, experimental design and data analysis of rotation studies have matured with long-term, longitudinal results generated. Examples include stress interactions, population dynamics of pathogenic races, SCN management recommendations, and crops for C and N sequestering. Rotated-corn is important in stress environments and must be considered in modern crop management planning due to yield advantages of 5 to 30% compared to continuous corn. The rotation effect lasts at most two years increasing yield 10 to 19% in the first year and 0 to 7% in the second. Tillage does not affect corn yield the first year following soybean, but improves corn yield 5% in the second year, and 9% in the third year. The mechanism for the rotation effect is unknown; one hypothesis is that one edaphic factor causes the effect, while another hypothesis implies multiple factors cause the effect and expression depends upon environment.