Effects Of Biochar And Phosphate Fertilizer Application On Soil Nutrients,Biomass And Plant Nutrient Contents Of Pakchoi

In this study,biochar(BC)was produced from rice straw through pyrolysis at five different temperatures(350,450,550,650,750℃).Effects of different pyrolysis temperature on the chemical properties of rice straw BC were analyzed.Then,the BC at 350℃(BC350)was selected,a pot experiment was carried out with different BC application rates(0,1.5%,3%)under the condition of different phosphate fertilizer application rates(0,50,100 kg·ha-1 P),to investigate the effects of BC and phosphate fertilizer alone or combined application on soil pH,nutrient contents,and C,N and P stoichiometry ratio,biomass,nutrient contents and C,N and P stoichiometry ratio of pakchoi(Brassica chinensis)plant,which can provide valuable information for the effective utilization of biomass resources,soil improvement and the safe production of vegetables in this region.The main results showed that the yield of BC gradually decreased with the increase of pyrolysis temperature,and greatly decreased at 350～650℃.There was significantly different in the yield of BC at 350℃,450℃,550℃ and 650℃(P<0.05).The pH of BC was greater than 7,and gradually increased and then gradually decreased with the increase of pyrolysis temperature,and reached the maximum at 550℃.The total carbon and total nitrogen content of BC decreased with the increase of pyrolysis temperature,and there was significantly different in the total carbon content of BC at 550℃,650℃and 750 ℃(P<0.05)while there was significantly different in the total nitrogen content of BC at 350℃,450℃ and 550℃(P<0.05).The C:N ratio of BC gradually increased,then significantly decreased with the increase of pyrolysis temperature,and reached the maximum at 550℃.The total phosphorus and total potassium content of BC gradually increased and then stabilized with the increase of pyrolysis temperature,the total phosphorus content of BC at 350℃,450℃,550℃ and 650℃ was significantly different(P<0.05)while the total potassium content of BC at 350℃,450℃ and 550℃was significantly different(P<0.05).The correlation analysis showed that the yield,pH and nutrient contents of BC were significantly correlated with the pyrolysis temperature.Compared with S(the control soil)treatment,BC alone or combined with phosphate fertilizer application all significantly increased soil pH,available phosphorus,available potassium,total carbon,total nitrogen and total phosphorus contents of soil,and the effects of 3%BC350 was significantly better than that of 1.5%BC350(P<0.05);phosphate fertilizer alone application had no significant effect on soil pH and total carbon content,but significantly increased soil available phosphorus and total phosphorus content,and significantly reduced soil available potassium and total nitrogen content.Compared with S(the control soil)treatment,the total potassium content of soil was not significantly increased with S + 1.5%BC350 treatment,but significantly increased with S+ 3%BC350 treatment;phosphate fertilizer alone or combined with BC application all significantly increased the total potassium content of soil(P<0.05).Compared with S(the control soil)treatment,BC application all significantly increased soil C:N ratio and C:P ratio no matter whether phosphate fertilizer application or not(P<0.05),and the effect of 3%BC350 was significantly better than that of 1.5%BC350(P<0.05);3%BC350 alone application significantly increased soil N:P ratio(P<0.05);when BC and phosphate fertilizer combined application,only S + P1 + 3%BC350 treatment significantly increased soil N:P ratio(P<0.05),S + PI + 1.5%BC350 and S + P2 + 3%BC350 treatment had no significant difference while S + P2 + 1.5%BC350 treatment significantly reduced the soil N:P ratio,phosphate fertilizer alone application also significantly reduced the soil N:P(P<0.05).Compared with S(the control soil)treatment,BC and phosphate fertilizer alone or combined application all significantly increased the biomass of pakchoi,and the effects of 1.5%BC350 on increasing biomass was significantly better than that of 3%BC350(P<0.05).Compared with S(the control soil)treatment,BC alone or combined with phosphate fertilizer application all reduced total carbon and total nitrogen content of pakchoi plants,but significantly increased total phosphorus and total potassium content and the improvement of 3%BC350 was better than that of 1.5%BC350(P<0.05);phosphate fertilizer alone application had no significant effects on total carbon content of pakchoi plants,but significantly increased total nitrogen and total phosphorus content,and significantly reduced total potassium content.Compared with S(the control soil)treatment,S + 3%BC350,S + PI + 1.5%BC350,S + P2 + 1.5%BC350 and S + P2 +3%BC350 significantly improved the C:N ratio of pakchoi plant(P<0.05);while biochar alone or combined with phosphate fertilizer application all significantly reduced the C:P ratio and N:P ratio(P<0.05),and decreased with the increase of BC application rates;phosphate fertilizer alone application also significantly reduced the C:P ratio and N:P ratio and decreased with the increase of phosphate fertilizer application rates(P<0.05).