Understanding the Effects of Cover Crops and Nutrient Management on Microbial Carbon Use Efficiency and Nitrogen Mineralization

View the project final report

Commodities

• Agronomic: corn

Practices

• Crop Production: cover crops, fertilizers, nutrient cycling, nutrient management
• Education and Training: decision support system, on-farm/ranch research
• Soil Management: nutrient mineralization

Microbial carbon use efficiency (CUE) is a critical property of the soil ecosystem that affects both carbon(C) storage and nitrogen (N) mineralization. Microbial CUE is the proportion of C in decomposing organic material that remains assimilated in microbial biomass rather than being respired as carbon dioxide. When microbial CUE is high, plant residue inputs are more effectively stabilized into soil organic matter. But increasing CUE reduces N-mineralization because microbial retention of C requires retention of N. This research will evaluate how soil texture, cover crop residue type, and N-fertilizer additions affect CUE in agricultural soils. Experiments will be conducted on two farmer fields and a research station in Pennsylvania for two years. Microbial CUE will be measured through oxygen isotope labeling, enzyme assays, and cover crop decomposition in litterbags. Microbial CUE will be related to soil properties, microbial community structure, and farm management factors to identify the relevant controlling factors. Finally, measured, and predicted values of CUE will be used to improve a new prototype decision support tool that predicts N-mineralization based on microbial processes and adjusts N-fertilizer recommendations accordingly. Results from the project will be disseminated through a co-learning workshop, a fact-sheet, farmer conferences, and an academic meeting. The improved understanding of CUE gained from this research will help farmers increase soil carbon storage as well as more precisely adjust N-fertilizer inputs based on predictions of N-mineralization from soil organic matter and crop residues, leading to greater farm profitability and fewer N losses to the environment from N over-fertilization. 

1. Evaluate and understand the effect of cover crop residues and the quantity and type of supplemental N fertilizer inputs on microbial carbon use efficiency.
2. Assess whether microbial communities (e.g., fungal: bacteria ratios, ammonia-oxidizing bacteria) respond to different availability of carbon and nitrogen resources and determine if this influences carbon use efficiency and enzyme activity
3. Determine if factors that control microbial CUE could be used to improve a nitrogen fertilizer recommendation tool that relies on an estimate of CUE to calculate N mineralization of cover crop residues and soil organic matter.
4. Compare corn yield response to supplemental N fertilizer additions to the recommended N application rate from the decision support tool and evaluate how adjusting CUE in the decision support tool with field measured CUE improves the tool’s prediction