Legumes in Crop Rotations Reduce Soil Nitrous Oxide Emissions Compared with Fertilized Non-Legume Rotations

Abstract

Soil nitrous oxide (N₂0) emissions were measured from a range of dryland crops and crop rotations in the northern grains region of Australia. The objective was to compare N₂0 emissions associated with the growth and post-harvest residue decomposition of a nitrogen (N₂)-fixing legume crop with that from N fertilized non-legume crops. From 2009 to 2012 a dryland crop rotation experiment was conducted on a black Vertosol (cracking clay soil) representative of the main soil type used for grain growing in the region. Crop rotation treatments were: canola + N_wheat + N_barley + N (CaWB), chickpea_wheat + N_barley (CpWB), chickpea_wheacchickpea (CpWCp), and chickpea_sorghum + N (CpS). Soil emissions of N₂0 were monitored in the field seven to eight times per day using an automated system of chambers connected to a gas chromatograph. Soil mineral N and plant N uptake were measured by regular field sampling. During the project, extremes of cold, hot, wet and dry weather were experienced that were often well below or above long-term averages for the site.