Nitrogen is the most limiting nutrient in agricultural ecosystems. Organic and sustainable farmers have limited options for nitrogen augmentation, yet are compelled to maximize yields to remain competitive. The use of composted manure amendments and cover crops have the potential to increase available nitrogen in the soil but the impact of these management strategies on soil microbial communities and biogeochemical processes is not thoroughly understood. The microbial mineralization carbon and nitrogen mineralization of organic matter could lead to loss of much of the carbon and nitrogen in natural amendments. The objective of this research is to determine how organic farming practices impact microbial communities and the biogeochemical processes they perform. This objective was investigated using the 20 year running Organic Crop Livestock Field (OCLF) experiment on the WVU organic research farm. The OCLF experiment has four management regimes: 1) no compost or livestock (control) 2) yearly compost addition (compost), 3) no compost with livestock rotation (livestock) 4). Plots without live stock were on a four-year crop rotation of corn, soybeans, wheat and kale/ rape, livestock integrated plots were on a seven-year rotation of the four crops plus three years spent in orchard grass/red clover pasture.
Results/Conclusions
Overall the long term management treatments impacted aspects of microbial community composition and biogeochemical processes. Compost addition with or without livestock led to an increase in the percent soil organic matter. Both livestock rotation and compost input influenced respiration rate and net nitrogen mineralization. Specifically, the livestock treatments exhibited increased respiration rates indicating increased soil activity. The plots that did not receive compost mineralized nitrogen while the compost added plots exhibited net nitrogen immobilization. These differences were tightly linked with shifts in microbial community structure. Wherein compost added plots had high fungal abundance while plots without compost had a greater proportion of bacteria and bacterial community structure was correlated with rates of net nitrogen mineralization. Overall these findings indicate that organic management practices drive microbial community structure and function. A better understanding of agroecosystem biogeochemistry is necessary to help inform management strategies in order to maximize plant nutrient use efficiency and reduce environmental damage that results from agriculture.