Quantifying the effect of biochar amendment on soil quality and crop productivity in Chinese rice paddies

China needs to produce about 20% more rice by 2030 to meet the growing demand for food that will result from population growth and economic development. This is not an easy task with soil quality being one of the major limiting factors. Improving the recycling of organic manures can be an important step toward stabilizing and optimizing soil quality in crop production systems. Recently, the pyrolysis conversion of crop straw into biochar and using it as a soil amendment has begun to attract increasing attention in China. Here, we performed a comprehensive analysis of 6 published studies with 11 field experiments to quantify the biochar amendment effect on soil quality and crop productivity in Chinese rice paddies. Our analysis showed that short-term application of biochar amendment had a positive effect on soil quality in rice paddies across a wide range of climates and soil types in China. However, the average effect of biochar amendment on rice yield was neutral. In contrast to biochar amendment, N fertilizer was less effective for improving soil quality but more effective for increasing rice yield. More interestingly, we found that biochar amendment had a positive effect on rice yield under N fertilizer application conditions, and there was a tight relationship between the effect of biochar amendment on rice yield and that on agronomic N use efficiency. The results lead us to conclude that further investigations are needed to determine (1) the long-term effect of biochar amendment on rice productivity, (2) the effect of biochar amendment on N uptake and metabolism in rice, and (3) the effect of biochar amendments produced from different feedstock and under different process conditions on soil quality and rice productivity in Chinese paddies.