Quantifying Nitrogen Mineralization and Plant Available Nitrogen Concentrations in the Soil Following Crop, Cover Crop Residue and Manure Incorporation Across An Organic Vegetable Rotation.

Providing adequate nitrogen fertilizer and synchronizing plant available nitrogen pool availability with crop nitrogen demands are great concerns in organic vegetable production. Net nitrogen mineralization quantity and rate, while affected by tillage, soil moisture, and soil temperature, varies with cover crop residue and organic amendment chemical composition. Within temperate crop species, C:N ratio, plant lignin and polyphenol concentrations have been used to predict net mineralization quantity and rate from amendments and cover crop residues added to the soil in laboratory mineralization studies. However, relatively little published literature exists on the in-situ analysis of nitrogen mineralization rates following amendment additions. Our goal was to determine in-situ nitrogen mineralization and plant available nitrogen pools as affected by previous crop, cover crop and manure residues alone and in combination within the soil. Specifically, our objectives were 1) In-situ quantification of nitrogen mineralized in soils following crop residue, cover crop residue, and composted poultry manure incorporation and 2) To determine plant available nitrogen concentrations with the soil, throughout a sweet corn crop growing under 5 organic fertility management systems. In-situ nitrogen mineralization rates were quantified using undisturbed soil columns with a resin-bead filled bag base. At the time of cover crop incorporation and after initial sampling, pre-weighed fertilizers and cover crop residues were added to each soil column. At predetermined intervals corresponding to critical periods of nitrogen demand in sweet corn, mineralization columns were extracted, sampled, and replaced within the soil. Plant available nitrogen pools were determined by taking 0-30 cm soil samples prior to planting, within season, and post harvest within each plot. Soil samples were analyzed for nitrate and ammonium concentrations. Data were analyzed using appropriate ANOVA and non-linear regression techniques to make comparisons within and between fertility management systems throughout the growing season. Analysis of the net nitrogen mineralization quantity and rates following five fertility management systems will allow recommendations for improved plant fertility management in organic vegetable rotations with cover crops.