Effects Of Biochar Additions On Rice Yield And Soil Fertility In Acid Paddy Field

Biochar has been widely suggested as an effective amendment to improve soil nutrient content and rice yield.However,the potential and aging of biochar on improve soil nutrient content and rice yield with different addition have not yet been definitively answered.We conducted a five-year(2015-2019)field experiment with the single factor randomized block design in an acidic paddy of South China(i.e.,Changsha,Hunan Province),to investigate(1)how does rice growth,rice productivity and soil fertility respond to different amount of biochar amendment(i.e.,0 t/hm~2(CK),20 t/hm~2(B20),40 t/hm~2(B40),60 t/hm~2(B60),80t/hm~2(B80),and 100 t/hm~2(B100);and(2)how long can the effects of biochar amendment sustain?Furthermore,according to the field experiment results of the previous two years,three levels of biochar amendment(i.e.,60 t/hm~2,80 t/hm~2 and 100 t/hm~2)were beneficial to improve crop productivity and soil fertility were selected.Then,we conducted a two-year(2017-2018)pot experiment with double factors randomized design(three levels of biochar amendment×three levels of fertilizer amendment)to investigate the potential of reduce the amount of fertilizer applied and nutrient loss in farmland.Three fertilizer levels include basal and fertilizer were reduced 30%,15%and normal fertilization,and with no added biochar but normal fertilization(CK)for comparison,a total of 10 treatments.Results showed that:(1)Leaf area index(LAI),SPAD of the reciprocal fourth leaf and dry matter accumulation at the heading stage increased with the increase amount of biochar amendment,so did the rice yield.Rice yield significantly correlated with LAI,SPAD value of the reciprocal fourth leaf,and dry matter accumulation at the heading stage,and significantly correlated with grain number per panicle.(2)The amount of biochar amendment significantly impacted its role in increasing rice yield.Rice yield significantly increased 17.0%～23.7%in the first year with≥60 t/hm~2biochar amendment compared with CK.The corresponding numbers for the other four years were 15.5%～32.4%rice yield increase with≥40 t/hm~2 biochar amendment in the second year,9.6%～21.8%rice yield increase with 20～100 t/hm~2 biochar amendment in the third year,no significant increase for all treatments in the fourth year,and 15.7%rice yield increase with100 t/hm~2 biochar amendment in the fifth year.Biochar amendment increased the accumulated rice yield for the consecutive five years by 9%～23.7%,5.5%～27.8%,6.8%～25.9%,5.4%～22.0%,and 4.6%～20.6%,respectively.(3)The application of biochar significantly improved soil p H value,the content of organic carbon,total phosphorus,total potassium,available phosphorus,available potassium,microbial biomass carbon and nitrogen contents,and enhanced the activities of phenol oxidase,peroxidase,acid phosphatase and urease in acid soil.And soil quality improved with the increase of biochar additions.(4)Soil organic carbon,PK available nutrients,soil microbial biomass and soil enzyme activity were significantly positively correlated with dry matter accumulation,grain number per panicle and yield.(5)The results of pot experiment showed that:although the amount of fertilization was decreased,rice yield was still significantly increased when biochar was applied≥60 t/hm~2.From 2017 to 2018,the annual increase in rice yield was 18%～29%,12%～22%respectively.Rice yield significantly correlated with grain number per panicle and seed setting rate.(6)Compared with controls(normal fertilization,not add biochar),although the amount of fertilization was reduced,soil p H,total phosphorus,total potassium,available phosphorus,available potassium,microbial biomass carbon,the activities of soil phenol oxidase,peroxidase,urease and acid phosphatase were significantly increased after the application of biochar.In conclusion,we found one-time add biochar is beneficial to improve soil p H,soil nutrient cycle,soil fertility,the quality of rice population,and ultimately promote the rice production on acidic paddy.And the effects were stronger with higher amount of biochar amendment(i.e.,80 t/hm~2and 100 t/hm~2).We also found these effects could last at least three years.Based on the changes of rice yield and soil quality,the optimal biochar addition amount of acidic rice field in this study was 60～80 t/hm~2.On this basis,even a 30%reduction in fertilization would not lead to the degradation of soil fertility and the reduction of rice yield.The findings of this study can extend our understanding of the long-term effects of biochar amendment on rice growth,rice productivity and soil fertility,and can also help farmers to increase rice yield through proper biochar amendment in acidic paddy.