Using interseeded cover crops to enhance nitrogen ecosystem services driven by plant-soil microbial relationships in agroecosystems

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Sarah A. Isbell and Jason P. Kaye, Department of Ecosystem Science and Management, Pennsylvania State University, University Park, PA, Sarah A. Isbell, Terrence H. Bell and Jason P. Kaye, Intercollege Graduate Degree Program in Ecology, The Pennsylvania State University, University Park, PA, Terrence H. Bell, Department of Plant Pathology and Environmental Microbiology, The Pennsylvania State University, University Park, PA

Background/Question/Methods
Nitrogen (N) management is a critical challenge with environmental and economic implications across local and global scales. Plant and soil microbial communities are drivers of N-cycling in terrestrial agroecosystems, and could be the target for management strategies that reduce N losses. Planting cover crops (CC), which are not harvested, can increase N retention and reduce nitrate leaching in agroecosystems. Here, we tested an innovative CC strategy, interseeding CCs into living cash crops. We hypothesized that interseeded CCs would reduce N losses through both increased N retention in plant biomass and in the associated soil microbial biomass. We expected an interseeded agroecosystem to have a distinct soil microbial community, and that the capacity of this community to store and cycle N would be impacted by soil N status. To test this, we planted a factorial field experiment in grain and silage maize with interseeded CCs, “standard practice” CCs, and no CCs at two rates of N application. We measured differences in N retention in CC biomass, soil inorganic N, microbial biomass, and soil bacterial communities.
Results/Conclusions
Inorganic soil N concentrations reveal that N retention was similar in interseeded systems as in the standard CC system, but greater than compared to the no CC system. In the low N addition treatment, total microbial biomass was similar among CC systems. However the high N systems increased microbial biomass in spring in the interseeded CC treatment relative to other CC treatments. Microbial community composition was different between seasons (fall and spring) and was impacted by soil N content, as well as by spring CC. This work shows that interseeding CCs may be a viable alternative to the standard CC practice for N retention services, and in some systems, such as those with excess soil N or large temporal niches available for CC growth, may outperform the standard practice. This work serves as a building block for advising land managers and growers on CC management and soil microbial regulators and provides a foundation for further research into manageable regulators of soil microbiomes across landscapes.