Abstract: Biochar prepared out of wheat straw was applied in reddish yellow paddy soil in Changsha of Hunan and red paddy soil in Jinxian of Jiangxi in a field experiment to explore for effects of biochar applied at a rate of 20 and 40 t·hm^-2,separately on yields of early and late rice and nitrogen recovery efficiency of late rice.It was found that the early rice didn′t respond much in yield to the combined application of nitrogen fertilizer and biochar,regardless of rate,in the two experiment sites,and neither the late rice in the experiment site of Changsha did,but the late rice at the experiment site of Jinxian did,increasing by 5.18% and 7.95%,separately,in the two treatments of 20 and 40 t·hm^-2 biochar.With the same N application rate,the treatments of 40 t·hm^-2 biochar in both experiment sites increased soil organic carbon by 55% or more over the control.Application of the biochar was found to increase pH in acid or weakly acid soil,lower soil bulk density and also increase nitrogen use efficiency of rice by 20.33 and 17.58 percentage point in the treatments of 40 t·hm^-2 biochar in the experiment sites of Changsha and Jinxian,respectively and nitrogen agronomic efficiency by 39.81% in Jinxian.The experiment demonstrates that biochar amendment in acid soil can stabilize or even increase rice yield and improve nitrogen use efficiency.

Key words: straw, biochar, paddy soil, rice, rice yield, nitrogen use efficiency