We designed full-size field trials to test the effectiveness of sorghum-maize intercropping at the UMass Crop and Animal Research and Education Farm in South Deerfield, MA. Plots of sorghum monocrop and maize monocrop served as controls with two intercropping systems, alternating row and mixed seeding intercropping. All four planting treatments were coupled with DMPP application to compare the biological inhibition of sorghum to an artificial inhibitor. Nitrogen and potassium fertilizers were applied in a manner similar to local practices, with DMPP application occurring concurrently. Plants were grown throughout the summer and harvested in early October for the 2021 and 2022 growing seasons to represent a typical corn system in Massachusetts.
The methodology of this work relies primarily on the capture and analysis of N2O gas leaving the soil, which represents a loss of nitrogen from the system as well as a problematic source of greenhouse gas emissions. To capture this gas flux, we implemented static chambers placed over the soil for a period of 30 minutes and sampled gas from the chamber every 15 minutes. Gas samples were loaded into pre-evacuated glass vials and analyzed through gas chromatography. To ascertain the temporal variability of N2O flux, these measurements were carried out throughout the New England summer every 2 or 3 days. This sampling scheme is more intensive than those typically employed in the literature, with many studies measuring gas flux on a weekly basis or longer gaps. The high frequency of sampling events allowed us to better account for stochastic variables in the system such as soil moisture and temperature fluctuations as they changed throughout the season.
In addition to gas flux, we collected data on soil temperature and moisture, as well as detailed atmospheric data from a nearby weather station at the research farm. At the end of the growing season, we collected above ground biomass from representative areas of each plot to measure bulk yield for silage production, the intended production outcome for this experiment.
To further understand the underlying mechanisms of the reduction in N2O flux we periodically and destructively took bulk soil and root samples for microbial community analysis. In this analysis we compared the abundance of microbial communities responsible for nitrogen transformations in the soil, mainly ammonia-oxidizing bacteria and archaea as well as denitrifying bacteria. We will also be coupling these comparisons to more broad observations of the microbial community structure at high resolution to get insights into how the wider microbial community responds to N2O reduction treatments and intercropping systems.
