Does Meta-analysis Adequately Assess the Interaction of the 4Rs of Crop Nutrition with Climate and Other Factors Impacting Nitrous Oxide Emissions?

English Abstract:

The growing global demands for food, fiber, and biofuel, and the human need for cleaner air and water, require better science-based N management decisions. Climate change, and wide fluctuations in crop and energy prices, are adding to the risks and complexities of crop and livestock production. Losses of nitrate to water resources, volatilization of ammonia, and emissions of nitrous oxide (N₂O) are growing environmental concerns that compound the nitrogen (N) management challenges in agriculture. Collectively, these issues highlight the need for management of crop nutrition that is more likely to result in increased crop N uptake and soil N retention. Meta analyses of recent research results in the corn-producing regions of the U.S. and Canada have shown that combining a urease inhibitor with a nitrification inhibitor was a crop N management strategy that consistently reduced direct N₂O emissions, but that conclusion was based on a relatively limited number of observations. It is becoming clear that N₂O emission response to the management of crop N nutrition varies across land resource regions and their associated cropping systems. Better choices for source, rate, time, and place of N application (the 4Rs of nutrient stewardship), in a well-implemented farm conservation plan, may reduce N₂O emissions by 10 to 50% in many fields. Investments in research on 4R nutrient stewardship, including more meta analyses of recent field research, might allow greater integration of crop N nutrition practices within regionally-calibrated predictive models. Such analyses and models may more effectively identify practices that may reduce N₂O emissions while continuing the pursuit of improved crop yields, a key requirement of emerging sustainability tracking systems applied to agriculture.