| Rice is the most important food crop in the China and is the staple food of more than60%of the Chinse population. But in recent years, rice yields have shown declining or stagnant trends in most provinces in China. Therefore, whether and how the rice production in China could meet the need of increasingly population growth with efficient resource utilization and environmental protection is a huge challenge for China. With a focus on Chinese major rice farming systems, the main objectives of the present study were to quantify and understand the interactive effects of biophysical factors (e.g. soil and rice farming type) and crop management practices on agronomic productivity and environmental impacts, and to evaluate total rice production, fertilizer N consumption, and emissions of two major greenhouse gases (GHGs, N2O and CH4) for major rice farming types and at national scale following alternative strategies. In that context, crop management practices are referred to as current farming practice (FP) and best management practice (BMP), with the latter representing relatively low-cost easily adoptable practices such as improved N and water management, cultivating healthy seedlings and increasing rice transplanting density. The mian results as follows:(1) The total N input(chemical fertilizer-N, organic fertilizer-N, wet deposition-N, irrigation-N and biological N fixation) were443.5kg N ha-1,297.0kg N ha-1and215.3kg N ha-1of farmer’s practice in double rice (D-R-S), single rice(S-R-S) in South of China and single rice in North of China (S-R-N), respectively; the chemical nitrogen fertilizer rate accouted for75.0%,68.2%and69.7%of the total nitrogen input; chemical nitrogen fertilizer uptake by rice and N fertilizer loss rate were34.8and32.1%,43.4%and33.5%.,42.1%and36.3%for D-R-S, S-R-S and S-R-N, respectively; the chemical nitrogen fertilizer residued in soil were33.1%,23.1%and21.7%for D-R-S, S-R-S and S-R-N, respectively; The paddy soils with low, moderate and high inherent productivity for early rice and late rice accouted for21.5%and21.3%,57.8%and65.6%,20.7%and13.1%of total rice cultivated areas; the paddy soils with low, moderate and high inherent productivity for single rice accouted for16.7%,76.2%and7.1%of total rice cultivated areas.(2) The differences in yield (yield gap) and partial factor productivity of nitrogen (PFP-N gap) among farmers across and within rice farming types were observed. BMPs and soil inherent productivity had different contribution to yield gap and PFP gap of various farmer’ yield level. Inherent soil productivity could explain yield gaps and PFP gaps of high, medium and low yield under FP by19.4%and43.0%,26.6%and44.2%,36.4%and51.3%over all the rice farming type; Adopting BMPs could explain the yield gap and PFP gap of high, medium and low yield under FP by47.7%and36.9%,35.9%and37.4%,30.5%and39.2%over all the rice farming types.(3) Inherent soil productivity, management practices and rice farming type resulted in confounded and interactive effects on greenhouse gas emissions (N2O, CH4and CO2-equivalent) with both trade-offs and compensating effects. Advances in nitrogen, water and crop management (BMPs) resulted in a substantial reduction in CO2-equivalent emission of rice farming despite a tradeoff of increase N2O emission. Cultivating inherently better soil also led to lower GHG intensity, despite a slight increase in GWP of N2O and CH4. CH4emission, GWP and GHGI followed the order late>early>single rice systems.(4) Compared to continuing the FP scenario, adoption of BMPs across the major single and double cropping systems would increase rice production in China by16.9×106Mg (10%) and a decrease in total fertilizer N consumption by1.0×106Mg (20%) and CO2-eq emissions by14.9×106Mg (9%). A strategy of increasing inherent soil productivity by1500kg ha-1for soils of low and moderate inherent productivity but with continued use of FPs could increase rice production by16.1×106Mg (10%). However, this would lead to a small increase in fertilizer N consumption of0.01×106Mg (0.1%) and GHG emissions (2%); The greatest benefit will be obtained by the combined adoption of BMPs and increased inherent soil productivity, leading to increases in total rice production by18%, with reductions in fertilizer N consumption and emissions of CO2-eq of22and7%. Major rice cropping systems had different contribution to Chinse rice production and environment, single rice had greater effect on increasing total rice production and double rice spcailly late rice had greater contribution to greenhouse gas emission mitigation. |
