Intercropping Effects On Organic Matter Accumulation and Soil Carbon and Nitrogen Dynamics in An Organic System: Does Plant Functional Diversity Play a Role?.

The introduction of multiple species in cropping systems is believed to play a major role in soil health and nutrient availability. Soil health is affected by a series of processes which are driven primarily by organic matter decomposition in the rhizosphere, otherwise known as the rhizosphere priming effect. Both above- and below-ground inputs in the form of plant and root residues can affect organic matter decomposition and, therefore, soil carbon and nitrogen dynamics based upon the total amount and quality (C:N) of residues being deposited. In diverse mixed cropping systems, it is believed that net primary productivity, and thus quantity and quality of inputs, is increased due to species interactions. We investigated different combinations of watermelon, peanut and okra in single crop and various intercropping combinations; each selected to perform a specific function within the system. Specifically, we assessed the effects of plant functional diversity on soil health (organic matter content, microbial, total and organic C and N) in an organic system. Simple regression analysis confirmed the justification of using dissolved organic carbon (DOC) to estimate soil microbial C with an R² value of 0.99 (p<.0001). However, contrary to our hypothesized outcome that an increase in plant diversity would result in an increase in microbial biomass C, preliminary results suggest a decrease in soil microbial C in the intercropping combination of peanut, watermelon and okra as compared to watermelon, peanut and okra grown in monocrop, 718, 941, 942 and 1189 µg C/g dry soil respectively (p=.0072). We are currently conducting analyses on above- and below-ground C and N inputs, in addition to total and organic soil C and N to help explain these observations and to determine if introducing plant functional diversity can be utilized as a tool to enhance soil health and nutrient cycling in small-acreage organic cropping systems.