Quantifying the effects of no till vegetable farming and organic mulch on greenhouse gas emissions and soil carbon
The broad objective of this project was to assess the potential of sustainable vegetable farming systems, developed by AHR and others, to reduce carbon dioxide (CO2) and nitrous oxide (N2O) emissions. This was achieved by first measuring greenhouse gas emissions and soil carbon (C) levels on common vegetable crops (processing potatoes, lettuce, broccoli and cabbage) grown using sprinkler irrigation and conventional nutrition and cultivation practices. Subsequently, no-tillage permanent beds, cover crops and organic mulches were established and the measurements repeated. Baseline N2O emissions were in the range of 50-100 ig N2O m-2 h-1, and spikes in N2O emissions were caused by nitrogen fertilizer applications and rainfall events. Methane (CH4) emissions were about 175 ig CH4 m-2 h-1, and were affected by rainfall events. CO2 emissions were highest for lucerne and annual rye cover crops, with emissions in the order of 940 mg CO2 m-2 h-1. Organic mulch, chicken manure and inorganic fertilizer treatments resulted in lower CO2 emissions of about 660-770 mg CO2 m-2 h-1. Organic mulch resulted in the greatest accumulation of soil C over time. The data collected is a valuable contribution to that currently available on greenhouse gas emissions and soil C for the Australian vegetable industry. Soil C levels and CO2 emissions were modelled using the Rothamsted carbon (RothC) model and predictions made for 100 years, for various land use scenarios. Organic mulch and annual rye cover crops resulted in the highest level of CO2 emissions and also the highest level of C sequestration in the soil. Inorganic fertilizer resulted in the lowest C emissions and sequestration. The work will be published in a recognised international scientific journal, as it represents some of the first baseline vegetable soil greenhouse gas emissions data available for the Australian vegetable industry.