Challenges facing the biogeochemical integrity of organic cropping systems.
Robertson, G *,1, 1 Michigan State University, Hickory Corners, MI
ABSTRACT- High productivity organic systems face the same biogeochemical challenge of conventional systems: how to get sufficient nutrients into the crop to maximize productivity while at the same time minimizing nutrient loss from the crop ecosystem. The challenge is especially acute for those nutrients that are either expensive or polluting or both, as in the case of nitrogen. Evidence suggests that organic varieties of field crops, if they differ from conventional varieties at all, are no more nutrient-efficient than conventional varieties. Thus nutrient efficiency must be achieved through management, and in particular through the timing, placement, and types of subsidies applied to the field. Does organic crop management in general minimize environmental harm from excess nutrients? For nitrogen and phosphorus, the two most harmful biogeochemical exports from croplands, the answer is an equivocal no. Nor is the answer always straightforward for carbon. Organic management provides different opportunities for achieving efficient nutrient use and carbon storage in field crops, but organic crops are not a priori less nutrient polluting than conventional agriculture popular opinion to the contrary. Providing nutrient conservation in organic systems, an important and potentially valuable ecosystem service that contributes to sustainability, is an elusive goal.
Key words: agricultural ecosystem, biogeochemistry, nitrogen and carbon cycling
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