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Oct 23, 2010
Organic management of vegetable and row crops in California's Central Valley has the potential to reduce net GHG emissions from soil by 3,496 kilograms (kg) of CO2-equivalents per hectare per year, compared to conventional management systems with standard tillage.
Conventional systems in the "Long-term Research on Agricultural Systems" (LTRAS) study resulted in net soil GHG emissions of 1,081 kg CO2-equivalents per hectare/year.
Accordingly, the organic system sequestered in the soil (i.e., reduced) approximately 2,400 kg CO2-equivalents per hectare per year – a very significant reduction.
In the LTRAS, conventional systems with conservation tillage performed about the same, and in some cases marginally worse, than the conventional system with standard tillage in terms of net soil GHG emissions.
Conventional systems with cover cropping did reduce net soil GHG emissions by about 1,000 kg/hectare/year, in effect making the conventional system+cover cropping neutral with respect to net soil GHG emissions.
Two striking insights emerge from this research.
In the quest to reduce agriculture's contribution to global warming, the most prominent and powerful coalition of agribusiness companies are promoting the combination of conservation tillage, GE seeds, and precision farming-guided fertilizer applications as the best way to reduce net GHG emissions. This study, along with others, shows why this combination of practices will bring about little or no change.
Conservation tillage, and even no-tillage does not result in appreciable, sustained soil carbon sequestration. The increase in soil organic matter in the top few inches of soil in no-till fields is accompanied by no increase or declines deeper in the soil profile.
GE seeds impact how farmers manage weeds and certain insects, but have marginal, if any impact on net GHG emissions.
Precision farming can bring about marginal gains in nitrogen use efficiency, and hence some reductions in nitrous oxide losses, but will do little to build soil organic matter and sequester substantial levels of carbon. The big gains from nutrient management come from incorporating cover crops plus animal manures in the soil profile.
Cover crops plus additions of compost and/or animal manures are core practices on organic farms in California, and indeed around the world. This California study shows that this combination of practices has the potential to turn significant GHG emissions into substantial reductions.
In addition, these same practices in organic systems help combat against yield losses in dry years, improve water quality, promote biodiversity and ecosystem stability, are safer for farm workers and consumers, and can increase net farm income. The major thing holding back the transition to organic fruit and vegetable production in California is consumer demand.
Source: De Gryze, S., et al., "Simulating greenhouse gas budgets of four California cropping systems under conventional and alternative management," Ecological Applications, Vol. 20, No. 7, pages 1805-1819. October 2010.
