Soil, fertility, crop nutrients, weed biomass and insect populations in organic and conventional field corn (Zea mays L.) agroecosystems

The objective of this study was to describe organic and conventional farms in farms in terms of the following variables: (1) seasonal dynamics of soil fertility, crop nutrient status and growth, and insect damage, (2) weed and insect abundance, and (3) soil nutrient availability and its relationship to grain quality, with focus on field corn, Zea mays L. These objectives were addressed on three pairs of organic and conventional farms in 1995 and 1996, and on six pairs of organic and conventional farms in 1998.;In 1995 and 1996, soil and plant nutrients fluctuated less on organic farms. Leaf amino N, predicted by near-infrared (NIR) spectroscopy, was significantly lower on organic farms in June when soil N was less available in organic systems. European corn borer damage was correlated positively with leaf amino N in June. In both years, conventional fields had more European corn borer damage, and yields were not significantly different between farming systems. These results suggest that optimal timing of N release may reduce insect damage by decreasing host suitability when the first generation of European corn borer is colonizing, without decreasing yields.;Organic fields had more annual grasses, but conventional fields had proportionally more perennial broadleaf weeds. Billbugs, armyworms, and cutworms caused more damage in organic fields, but only cutworms exceeded the economic threshold. Parasitic wasps and predatory bugs were generally more abundant in organic systems, whereas conventional systems favored lady beetles and green lacewings, predators that preferentially feed on aphids.;In an additional study, a higher proportion of soil N was immobilized by microbes in four of six organic fields, indicating a larger role of microbes in regulating nutrient availability in organic fields. Grain from organic fields had a significantly higher concentration of high-quality (non-zein) protein than grain from conventional fields. The ratio of zein to non-zein protein was negatively correlated with the ratio of microbial N to NO 3, indicating an increase in grain quality with enhanced role of soil microbes in regulating soil nutrient availability.;This information will be used to identify soil management practices that optimize crop productivity and limit insect pest levels.