Nutrient and Weed Management in Organic Sweet Corn Systems in the Central Sands of Wisconsin.

The Central Sands region of Wisconsin is host to commercial-scale conventional vegetable production. Significant water quality problems due to pesticide and synthetic fertilizer leaching and runoff plague the region, making organic management appealing to many growers. However, weed management is an enduring challenge to large-scale organic vegetable production because weeds compete for nutrients in fertilized soils and herbicide application is not permitted in organic systems. The goal of this research is to develop nutrient and weed management programs that will decrease agronomic and economic risk associated with conversion to organic systems thus increasing adoption of organic management practices in this region. Three nitrogen inputs were evaluated: spring-seeded field pea, composted poultry manure, and feather meal. Data collected include yield; biomass of corn, weeds, and field pea; nitrogen uptake in corn, weeds, and field pea; and post-harvest soil nitrate. The first year of data collection demonstrated a positive response to nitrogen fertilization with maximum yields between 16 and 21 tons of corn per hectare at 169 to 225 kilograms nitrogen per hectare, but little system effect attributable to green manure or animal manure systems or difference in weed management. This is likely due to inherently low levels of plant-available nitrogen in organic amendments and very fast mineralization and leaching potential of nutrients in sandy soil. The second year of data collection was expanded to include regular soil testing for nitrate to track nitrogen mineralization in these systems and thus hone nutrient crediting and application timing. At this time we cannot recommend use of pre-season organic amendments in sandy soil that cannot retain plant-available nitrogen as it mineralizes.