Objectives:

• Develop and refine an existing model into a decision support tool for organic farmers to determine the ENOR for their corn crop that considers N contributions from SOM and decomposing cover crop residues.
• Test the model’s capacity to predict corn N requirements on a wide range of soil textures and SOM levels, and evaluate assumed values used in the model.
• Develop the model into an online tool that accurately predicts EONR based on information entered by the user including %SOM, soil texture, N content and C:N ratio of cover crops, yield goal, N fertilizer cost, and farmgate price for corn.
• Deliver the N decision support tool to farmers through multiple outreach venues.

Replicated field trials were conducted at the Penn State research station and several organic farms representing a range of soil textures and SOM levels. Corn was grown after several different cover crops, whose biomass, N content, and C:N ratio were measured at termination. Corn received 0, 50%, 100%, or 150% of the N recommended by the current version of the tool, using poultry feather meal (13-0-0), and corn grain yield and aboveground residue biomass were measured.

The prototype N decision tool, which included yield response curves from field trials and partial budget analysis, was tested by farmer participants in the project. The tool was refined and retested in an iterative process each year of the project. Improvements addressed the impacts of a wider range of soil textures and variations in actual C:N ratios of microbial biomass and SOM on N mineralization.