Reducing nitrous oxide emissions from sugarcane soil with legume intercropping

Monica Elizabeth Salazar Cajas1, Nicole Robinson1, Adam Royle2, Lawrence Di Bella2, Weijin Wang3, Marijke Heenan3, Steven Reeves3, Susanne Schmidt1, Richard Brackin1

1 School of Agriculture and Food Sciences, The University of Queensland, QLD, 4072 Brisbane, Australia; email: [email protected]

2 Herbert Cane Productivity Services Limited, 181 Fairford Rd, Ingham QLD 4850, Australia

3 Department of Science, Information Technology and Innovation, 41 Boggo Road, Dutton Park, QLD 4102 Australia

Abstract

Australian sugarcane cropping has low nitrogen (N) use efficiencies, largely due to a mismatch of early-season N fertiliser application and later season peak crop N demand, in combination with poor soils and wet climate. To address the problem of N losses via run-off, leaching and N2O emissions, the sugarcane industry is evaluating several avenues. One approach is to improve N use efficiency (NUE) by reducing the use of vulnerable-to-loss N fertiliser, supplementing crop needs with biologically fixed N via sugarcane-legume intercropping. In an optimised system, decomposing legumes would deliver N to sugarcane, synchronised with sugarcane’s long N accumulation phase. We hypothesised that legume intercropping in combination with lower N fertiliser rates will reduce N losses (N2O emissions were quantified here) but not sugar yields. Here we report on one of several field trials with sugarcane grown as monoculture or intercropped with legumes at full N fertiliser or lowered rates (67 or 41% of full N). In the second year of implementation and compared to full N fertiliser, N2O emissions were reduced by 50 to 70% in the 67% N treatments irrespective of legume presence. Highest sugarcane biomass was achieved with full-N rate, 67% N, and 67% N + soybean intercropping. Sugarcane production was reduced in 67% N + mung bean intercropping, 41% N and zero N treatments. Sugar yield was variable but statistically similar across all treatments. These early results indicate that evaluation across different growing regions, fertiliser rates and planting times are needed to optimise sugarcane-legume intercropping systems.