Pinto peanut cover crop nitrogen contributions and potential to mitigate nitrous oxide emissions in subtropical coffee plantations

Many coffee (Coffea arabica L) production systems are characterised by high use of nitrogen (N) fertilisers, which can result in N leaching and emissions of nitrous oxide (N₂O). We investigated the potential for legume cover crops grown inter-row to provide N for coffee trees and lower seasonal N₂O emissions compared to poultry litter amendment at two subtropical field sites over 12 months, with unfertilised traditional grass groundcover used as a control treatment. Groundcovers (legume and grass treatments) were slashed from the inter-row into the tree line every 2-6 weeks as per normal farming operations. The prostrate ground cover legume Pinto peanut (Arachis pintoi) produced 4-5 t ha^-1 biomass at both sites over the 12 month period, and fixed 146 kg N ha^-1 year^-1 at one site as estimated using the ¹⁵N natural abundance method. Background emissions from soil were lower at site 1 (0.38 kg N₂O-N ha^-1 year^-1) than site 2 (2.26 kg N₂O-N ha^-1 year^-1) reflecting differences in soil N and C levels at the sites. The use of Pinto peanut residues as an N amendment didn't result in any N₂O flux events beyond those observed in the traditional groundcover control treatment across the season at either site, while the application of poultry litter to match farmer practice at these sites led to a major emission event. Ultimately, the Pinto peanut cover crop treatment led to a lower emission factor than for poultry litter at both sites, and resulted in significantly lower cumulative seasonal emissions for the legume cover crop (0.34 kg N₂O-N ha^-1 season^-1) than poultry litter amendment (0.68 kg N₂O-N ha^-1 season^-1) at site 1 despite similar inputs of N into the system. These findings suggest cover crop legumes could be integrated into coffee plantations to offset a portion of external N inputs, while lowering N₂O emissions.