Effects of combined applications of biochar and reduced phosphate fertilizer on phosphorus forms in acid paddy soil of southern China
To address the issue of strong ability of southern acidic soils to adsorb and fix phosphorus specifically,this study used a micro-area experiment to investigate the effects of combined applications of biochar(40,60 and 80 t/hm2)and reduced phosphate-fertilizer(P2O5 75,60,45 and 30 kg/hm2)on the contents of different forms of phosphorus.Additional treatment was set up as control(CK).CK was fertilization of P2O5 75 kg/hm2 without biochar application.The results were as follows:(1)Combined applications of biochar and reduced phosphate fertilizer significantly increased the content of total phosphorus,available phosphorus,resin phosphorus,sodium bicarbonate inorganic phosphorus,diluted hydrochloric acid phosphorus,but significantly decreased the content of residual phosphorus.(2)The treatments of≥45 kg/hm2 phosphorus fertilizer application significantly increased soil total phosphorus and available phosphorus by 17.1%-46.7%and 32.5%-76.3%,compared with the control.(3)The treatments of≥45 kg/hm2 phosphorus fertilizer application significantly increased the contents of soil resin phosphorus and sodium bicarbonate inorganic phosphorus by 50.8%-160.3%and 36.1%-118.3%,respectively,compared with the control.(4)Compared with the control,phosphorus fertilizer reduction resulted in a decrease in soil organic phosphorus content of sodium hydroxide by 38.4%-39.8%,but there was no significant difference in soil inorganic phosphorus content of sodium hydroxide between treatments.(5)The content of diluted hydrochloric acid phosphorus was significantly increased by 57.9%-352.1%after biochar application,compared with the control.The organic content of concentrated hydrochloric phosphorus was significantly lower in the phosphorus fertilizer reduction treatment than in the normal phosphorus application with biochar.The inorganic content of concentrated hydrochloric phosphorus was significantly lower in the phosphorus fertilization level of 30 kg/hm2 than in the other phosphorus fertilization and biochar treatment combinations.The application of biochar significantly reduced the content of residual phosphorus in the soil.(6)The contents of soil total phosphorus and available phosphorus were positively correlated with the contents of resin phosphorus,inorganic phosphorus in sodium bicarbonate,and diluted hydrochloric acid phosphorus.In conclusion,biochar application is beneficial to improve the phosphorus content of the acidic southern paddy soil,promote the conversion of organic phosphorus to inorganic phosphorus and improve the effectiveness of soil phosphorus,on which the phosphorus fertilizer application can be as low as 45 kg/hm2.
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