Effects of biochar amendment on rice growth and nitrogen retention in a waterlogged paddy field

Overuse of chemical fertilizer in agriculture has caused serious nitrogen (N) loss and water pollution problems in China. Biochar has the potential ability to reduce N loss and increase crop yield. However, there is still limited knowledge of the impacts of different biochars on N loss and crop yield over agriculturally relevant time frames. In this study, we compared the effects of amendment with bamboo biochar and rice straw biochar on the N retention and rice productivity in paddy fields, over an agriculturally relevant time span of 2 years. A 2-year field study was conducted to investigate the effects of bamboo biochar and rice straw biochar amendment at a rate of 22.5 t ha(-1) (with or without urea) on N retention and rice growth. Total nitrogen (TN), ammonia (NH4 (+)-N), and nitrate (NO3 (-)-N) in soil and surface water were determined after biochar application. Stem lengths and rice yield were monitored during the experiment. Amendment with rice straw biochar resulted in higher rice yields than in paddy soils that had bamboo biochar amendments. Incorporating rice straw biochar into a paddy field increased the rice yield by 19.8 % in 2009 and 21.6 % in 2010 without urea (P < 0.05) and by 11.3 % in 2009 (P < 0.05) and 14.4 % in 2010 with urea, compared with their corresponding control treatments. Although there were no significant impacts on the surface water N runoff potential, biochar amendment did result in a significant increase in the NO3 (-)-N content of rhizosphere soil-121.2-135.7 % with urea and 89.7-102.2 % without urea, respectively, at the tillering stage in the first year (P < 0.05). These results show that carbonizing rice straw residue into biochar and incorporating it into soil has the potential to enhance rice productivity and N retention in a paddy field.