Effects Of Returning Straw And Biochar To Fields On Nitrogen Availability In Tropical Soil-rice System

In order to clarify the effects of straw returning and carbonization returning on tropical soil fertility,nitrogen gaseous loss,nitrogen uptake and yield by rice,pot experiment was conducted to study the effects of straw returning and biochar on rice yield and its composition,soil properties,ammonia volatilization,greenhouse gas emission and rice nitrogen uptake.Six treatments including no nitrogen（0N）,no nitrogen straw returning（ST）,no nitrogen biochar treatment（BI）,conventional fertilization（CF）,straw returning with nitrogen fertilizer（NST）and biochar combined with nitrogen fertilizer treatment（NBI）were designed.The effects of straw and biochar returning on soil properties,nitrogen loss,greenhouse gas emission,rice yield and its components and nitrogen balance were studied.The main results are as follows:1.Straw returning significantly decreased soil p H at rice tillering stage and panicle differentiation stage.At the rice maturity stage,the soil urease activity and dehydrogenase activity of NBI treatment were significantly higher than those of others（P<0.05）.2.Nitrogen application increased the contents of soil NH₄⁺-N,soluble organic nitrogen（DON）and acid-hydrolyzable ammonium nitrogen（HAN）at the rice maturity stage.At the rice maturity stage,compared with CF,ST and NST treatments significantly promoted soil amino acid nitrogen（AAN）content at tillering stage.NBI treatment significantly increased the contents of NH₄⁺-N,soluble organic nitrogen（DON）,amino acid nitrogen（AAN）and acidolysis NH₄⁺-N in soil at maturity stage（P<0.05）.3.NST treatment significantly reduced the p H of overlying water at rice tillering stage and panicle differentiation stage,and increased the NH₄⁺-N concentration of overlying water.The cumulative ammonia volatilization emission of biochar combined with nitrogen fertilizer was significantly reduced by 28.9%,which had a good inhibition effect on ammonia volatilization in paddy fields.4.CH₄ emission mainly occurred at rice tillering stage and panicle differentiation stage.CH₄emission of fertilization treatment was higher than that of non-fertilization treatment.straw returning significantly increased CH₄ emission of paddy field.Both of straw returning and biochar contributed to the reduction of N₂O emission（P<0.05）.Compared with CF treatment,NBI treatment significantly reduced CH₄ and N₂O emissions.5.Compared with the control,ST treatment significantly increased the plant height（P<0.05）.The grain number per spike and theoretical yield of NST treatment are the highest among all treatments.6.The nitrogen of rice gradually transferred to grain with the growth period.The nitrogen uptake by plants mainly occurred in rice panicle differentiation stage and maturity stage.The ratio of soil residue nitrogen to input nitrogen and soil basic nitrogen was 40.41%～45.56%,plant uptake was 17.87%～22.82%,and nitrogen loss was 31.62%～41.68%.Soil residual nitrogen in NST and NBI treatments was significantly higher than that of CF treatments,and nitrogen loss ratio of NST treatment significantly decreased.