A Better Way to Measure Cover Crop Nitrogen

Cover crops do more than hold soil in place over the winter. They can also feed the next cash crop by returning nitrogen to the ground. The hard part for farmers has always been knowing how much nitrogen they can count on. The Cover Crop Nitrogen tool developed by Penn State researchers and validated by graduate students, is built to answer exactly that question. It estimates the nitrogen a cover crop puts back into the soil and accounts for factors like soil texture, which makes it useful across Pennsylvania and surrounding states. 

For years, farmers have leaned on the Penn State Agronomy Guide to guide their nitrogen application decisions. However, the guide doesn't account for how conditions on individual farms might affect nitrogen demand. The new tool is more accurate, using soil tests and other inputs to give a clearer picture of what is already in the field. It also weighs the value of the nitrogen against the value of the crop, helping farmers see how much fertilizer actually pays off. The Graphical Interface to Determine Cover Crop and Soil Organic Matter N Credits tool is available for farmers to use. 

This summer, Copenhaver set up on-farm experiments on two working farms in Pennsylvania, along with trials at Russell E. Larson Agricultural Research Center in Centre County. The working farms have different crop rotation histories but follow a double-crop system popular on dairy farms, growing corn for silage and then a forage crop in a single year, often with manure as a nitrogen source. Managing nitrogen needs is more complex on dairy farms, where fields receive lots of manure in addition to what’s provided by cover crops and fertilizers. 

Copenhaver is testing how the cover crop nitrogen tool estimates the cover crop stubble left over by harvested annual forages in double-cropping dairy systems. Recalibration of the tool may be necessary so that dairy farms in double-cropping systems will be able to estimate the economic nitrogen optimum rate (ENOR) for their silage corn crop.  

She is also taking samples to run other nitrogen estimation tools like PSNT and CSNT to demonstrate how well they estimate corn nitrogen. In setting up trials that test nitrogen rates incremented starting from zero added synthetic fertilizer to over the recommendation of the tools, Copenhaver and her colleagues may develop a nitrogen response curve that correlates with added N and yield.  

For Copenhaver, the most rewarding part of the project is that it happens on real farms and directly involves the farmers who will use the results. It's improving sustainability on farms by helping them use nitrogen more efficiently. Farmers have been phasing out alfalfa hay in their dairy rotations in favor of the double-crop system. Without alfalfa adding free N from the atmosphere, and the double cropping system demanding lots of nitrogen, there’s a greater need for efficient, optimized nitrogen application. When nitrogen is lost into the air or groundwater, farmers are not getting full value from their resources, resulting in a loss of money in addition to the associated negative environmental impacts.  So, a tool that helps farmers apply just the right amount of nitrogen is a meaningful step toward better farming. Please check out the Graphical Interface to Determine Cover Crop and Soil Organic Matter N Credits and stay tuned for updates as the nitrogen tool is calibrated to interface with double-crop dairy rotations.