Crediting cover crops and soil organic matter in a variable rate nitrogen fertilizer prescription

View the project final report

Commodities

• Agronomic: corn

Practices

• Crop Production: application rate management, catch crops, cover crops, fertilizers, nutrient cycling, nutrient management
• Soil Management: green manures, nutrient mineralization, organic matter, soil quality/health

Nitrogen (N) mineralized from cover crop residues and soil organic matter is an important nutrient source for crop
growth, but N fertilizer application rates to corn often do not account for these N sources. This contributes to a
low fertilizer nitrogen use efficiency (NUE) in corn production systems and leads to environmental pollution from N
fertilizer losses (1). Recent advances in predicting the N supplied to corn by cover crops and soil organic matter
provide a quantitative framework for crediting these sources when calculating N fertilizer application rates (2, 3).
Furthermore, existing precision agriculture technologies could be utilized to generate spatially explicit predictions
of biological N supply, which could inform variable rate N fertilizer applications. In this project we will use
apparent electrical conductivity (ECa) sensors to delineate sampling zones for measuring soil organic matter and
soil texture, map cover biomass N content at the time of termination with a normalized difference vegetation index
(NDVI) crop sensor, and use recently developed equations to predict N supply from cover crops and soil organic
matter. We will then use the map of biological N supply to create prescription files for the variable rate application
of urea-N fertilizer at corn planting. We hypothesize that a variable rate N application will increase NUE while
maintaining similar corn yields to a fixed fertilizer rate control. Results and methodology of the project will be
shared with ag service providers and farmers through conference presentations, field day demonstrations,
electronic newsletters and extension fact sheets.

Our goal is to decrease N pollution in the environment and increase farmer profitability by improving NUE in corn
production. Our research question is whether the spatially explicit crediting of biological N supply from cover
crops and soil organic matter when calculating a variable rate N fertilizer prescription can improve fertilizer NUE.
The first objective is to use precision agriculture technologies to map cover crop biomass N content and delineate
soil sampling zones for the measurement of soil organic matter and soil texture. The second objective is to use the maps of cover crop biomass N, soil organic matter, and soil texture to calculate spatially explicit biological N
supply credits. The third objective is to use the map of biological N supply credits to calculate variable rate N
fertilizer prescriptions and measure whether NUE improves and overall corn yields can be maintained by using a
variable rate application compared to the standard practice of a fixed N rate.