Farmland occupies approximately 915 million acres in the US, with cropland making up about a third of this, a little more than 13% of the country. Characterized by frequent disturbance and disproportionally high nutrient inputs, agroecosystems have the potential to impact the global cycling of carbon and nitrogen. However, due to the diversity of crop management practices there is a lot of variability in carbon and nitrogen cycling and storage. Sustainable agricultural practices must balance crop productivity with environmental impacts such as nitrate leaching. More research is needed to develop a thorough understanding of the effect management practices have on the composition and function of soil microbial communities. To study the long-term impacts of compost application and pasture integration in crop rotation, samples were collected from the existing Organic Crop Livestock Field (OCLF) experiment on the WVU organic research farm. The 19-year-old OCLF experiment has a traditional four-year rotation of corn, soybeans, wheat and kale/rape, and a pasture integrated seven-year rotation of the four crops followed by three years spent in orchard grass/red clover pasture, each with compost amended and no-input control treatments.
Results/Conclusions
The compost-input and pasture integrated rotation treatments increased soil organic matter, respiration, and extracellular enzyme activity, suggesting enhanced soil microbial activity. Soil prokaryotic community composition was affected by the long-term treatments. For instance, the relative abundance of ammonia oxidizing archaea was greater in soils that received compost, however this effect was reduced in the pasture integrated rotation. Similarly, the compost addition led to higher rates of potential nitrification early in the season, which was greatly mitigated by the pasture integration. These effects on the microbial community composition and function could underlie the variation in soil nitrate concentrations among the treatments. Early in the season, compost amendment produced high nitrate levels in the traditional but not in the pasture integrated rotation. Taken together these results suggest the difference in nitrate levels could result from more nitrate production, rather than less nitrate loss from leaching or denitrification. This link between nitrifier abundance, nitrification rates, and nitrate levels indicates that the long-term integration of pasture in crop rotation has the potential to reduce nitrogen leaching early in the growing season. As crop yields were unaffected by pasture integration, this management practice could reduce the potential for negative environmental impacts without reducing productivity.