Increasing nitrogen (N) and phosphorus (P) inputs have greatly contributed to the increasing food production in China during the last decades, but have also increased N and P losses to the environment. The pathways and magnitude of these losses are not well quantified. Here, we report on N and P use efficiencies and losses at a national scale in 2005, using the model NUFER (NUtrient flows in Food chains, Environment and Resources use). Total amount of "new" N imported to the food chain was 48.8 Tg in 2005. Only 4.4.Tg reached households as food. Average N use efficiencies in crop production, animal production, and the whole food chain were 26, 11, and 9%, respectively. Most of the imported N was lost to the environment, that is, 23 Tg N to atmosphere, as ammonia (57%), nitrous oxide (2%), dinitrogen (33%), and nitrogen oxides (8%), and 20 Tg to waters. The total P input into the food chain was 7.8 Tg. The average P use efficiencies in crop production, animal production, and the whole food chain were 36, 5, and 7%, respectively. This is the first comprehensive overview of N and P balances, losses, and use efficiencies of the food chain in China. It shows that the N and P costs of food are high (for N 11 kg kg(-1), for P 13 kg kg(-1)). Key measures for lowering the N and P costs of food production are (i) increasing crop and animal production, (ii) balanced fertilization, and (iii) improved manure management.
During the past 50 years, China has successfully realized food self-sufficiency for its rapidly growing population. Currently, it feeds 22% of the global population with 9% of the global area of arable land. However, these achievements were made at high external resource use and environmental costs. The challenge facing China is to further increase food production while drastically decreasing the environmental costs of food production. Here we review the major developments in nutrient management in China over the last 50 years. We briefly analyze the current organizational structure of the "advisory system" in agriculture, the developments in nutrient management for crop production, and the developments in nutrient management in animal production. We then discuss the nutrient management challenges for the next decades, considering nutrient management in the whole chain of crop production-animal production-food processing-food consumption by households. We argue that more coherent national policies and institutional structures are required for research extension education to be able to address the immense challenges ahead. Key actions include nutrient management in the whole food chain concomitant with a shift in objectives from food security only to food security, resource use efficiency, and environmental sustainability; improved animal waste management based on coupled animal production and crop production systems; and much greater emphasis on technology transfer from science to practice through education, training, demonstration, and extension services.
Abstract. Although the concept of producing higher yields with reduced greenhouse gas (GHG) emissions is a goal that attracts increasing public and scientific attention, the trade-off between high yields and GHG emissions in intensive agricultural production is not well understood. Here, we hypothesize that there exists a mechanistic relationship between wheat grain yield and GHG emission, and that could be transformed into better agronomic management. A total 33 sites of on-farm experiments were investigated to evaluate the relationship between grain yield and GHG emissions using two systems (conventional practice, CP; high-yielding systems, HY) of intensive winter wheat (Triticum aestivum L.) in China. Furthermore, we discussed the potential to produce higher yields with lower GHG emissions based on a survey of 2938 farmers. Compared to the CP system, grain yield was 39% (2352 kg ha−1) higher in the HY system, while GHG emissions increased by only 10%, and GHG emission intensity was reduced by 21%. The current intensive winter wheat system with farmers' practice had a median yield and maximum GHG emission rate of 6050 kg ha−1 and 4783 kg CO2 eq ha−1, respectively; however, this system can be transformed to maintain yields while reducing GHG emissions by 26% (6077 kg ha−1, and 3555 kg CO2 eq ha−1). Further, the HY system was found to increase grain yield by 39% with a simultaneous reduction in GHG emissions by 18% (8429 kg ha−1, and 3905 kg CO2 eq ha−1, respectively). In the future, we suggest moving the trade-off relationships and calculations from grain yield and GHG emissions to new measures of productivity and environmental protection using innovative management technologies.
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