2016 International Conference on Clean Water, Air & Soil (CleanWAS 2016)

93 / 2016-06-27 11:14:20

USE OF LEGUME CROP ROTATION TO IMPROVE SOIL HEALTH AND MITIGATE GREENHOUSE GAS EMISSION AND NITROGEN POLLUTION

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Growing legumes can reduce the population of soil pathogens, add extra quantities of nitrogen (N) into soil through biological N fixation, and help conserve soil mineral N in the biomass, which could otherwise be lost during the fallow period. The legume crop residues can contain 50-300 kg N per hectare and thus can substantially reduce or even eliminate N fertiliser application in the following season. The organic N in the legume residues can be easily mineralised, especially after incorporation of the biomass into soil by tillage. If not used by plants, the mineral N, particularly nitrate (NO3-), can be lost through leaching or runoff, and eventually cause pollution in water ways. Nitrate is also highly susceptible to denitrification upon heavy rainfall or irrigation, which leads to N2 gas loss and emission of the potent greenhouse gas nitrous oxide (N2O).
A range of management strategies have the capacity to minimise legume residue N loss and thus to maximise the economic and environmental benefits of legume rotation in agriculture. These strategies generally centre around three principles: (1) holding the mineral N in the relatively stable ammonium (NH4+) form as much as possible (i.e., inhibiting nitrification); (2) manipulating N mineralisation of the legume residues; and (3) capturing the mineral N before it is lost. We investigated the effects of legume rotation and several crop residue management strategies on N2O emissions, N downward movement in soil profile, crop yield and profitability in sugarcane cropping systems in tropical and subtropical Australia. The results will be discussed in the presentation.