Mechanism Of Biochar Effects On Nitrogen And Phosphorus Of Cotton Uptake Under Drip Irrigation Conditions

[Object] Biochar can improve soil fertility,reduce soil nutrient loss,and increase crop yield and nutrient utilization efficiency.The properties and mechanism of different biochar were varied from the raw materials for biochar producing.Three types of biochar were produced from cotton straw,corn con,and poultry manure,respectively.The objective of this study is to investigate?1?the change of forms and concentrations of N and P in soil amended by different biochar;?2?root growth and nutrient uptake of cotton influenced by different biochar;?3?the mechanism of cotton nutrient use efficiency influenced by biochar.This research will benefit the reasonable application of biochar.[Method] A field experiment was conducted to investigate the differences in soil nutrient and cotton growth among three types of biochar from 2014 to 2015.The experiment consisted of a 4 × 2 factorial design with four biochar treatments and two P application rates.The four biochar treatments were?1?no amendment?CK?,?2?cotton straw biochar?CB?,?3?maize cob biochar?MB?and?4?poultry manure biochar?PB?.The P application rates were set as 0 and 105 kg P₂O₅/ha?noted as P0 and P105,respectively?.The mechanism of biochar effect on cotton nutrient uptake was conducted with a root-bag field experiment in 2016.The four treatments of cotton straw biochar application were set as?1?no amendment?CK?,?2?applied biochar inside root bag?CBN?,?3?applied biochar outside root bag?CBW?and?4?applied biochar both inside and outside root bag?CB?.The P application rates were 0 and 105 kg P₂O₅/ha?noted as P0 and P105?.[Result]?1?The soil NO₃-N concentration at 0⁴0 cm depth was increased by poultry manure biochar treatment?PB?during the early stage of cotton growth season and promoted by cotton straw biochar treatment?CB?during the mid-and late-stage of cotton growth season.The application of maize cob biochar?MB?had a little effect on soil NO₃--N concentration at 0⁴0 cm depth,but the residual NO₃--N of soil in MB was significantly higher than that in CK.Nitrogen uptake of cotton was increased significantly by biochar application.The N contents of cotton in CB,PB,and MB treatments were 34.3%,24.8%,and15.5% higher than in CK,respectively.The application of poultry manure biochar and cotton straw biochar reduced significantly apparent N loss and N surplus of soil.The apparent N loss and N surplus of soil in CB treatment were 63.2% and 46.0% lower than those in CK.?2?Three types of biochar increased significantly the concentrations of total P,available P,and water soluble P in soil.The highest of soil available P and water soluble P were found in PB treatment,and then in CB and MB treatments.The root weight of cotton under both no-P and fertilized P conditions and the root length density?RLD?under no-P conditions were significantly higher in PB,CB,and MB treatments than those in CK,but there were no significant differences among PB,CB,and MB treatments.In the no P plots,the average diameter,surface area,and volume of cotton root were significant higher in PB treatment than those in CK.In the P fertilized plots,CB treatment increased significantly the average diameter,surface area,and volume of cotton root.?3?Biomass,P uptake,and yield of cotton were increased significantly with three types of biochar amendment.Cotton biomass in PB and CB treatments were significant higher than that in MB treatment.Cotton P uptake were significant higher in PB and MB treatments than in CB treatment under no P conditions,however,there were no significant differences among three types of biochar treatments under P fertilized conditions.PB treatment had the highest yield of cotton,and then was CB and MB treatments,and the lowest cotton yield was found in CK treatment.Three types of biochar application increased significantly P fertilizer use efficiency of cotton.The highest P fertilizer use efficiency was found in CB treatment,which represented 186% and 95% higher than CK in 2014 and 2015,respectively.?4?Cotton straw biochar amendment increased significantly the concentrations of soil resin-P,Na HCO₃-P,and Na OH-P,but had a little effect on HCl-P and Residue-P concentrations in 2016.In the no Pplots,the concentrations of soil resin-P,Na HCO₃-P,and Na OH-P in CB treatments?CBN,CBW,CB?were17.6% ? 50.7%,and 27.2% higher than those in CK,respectively.However,there were no significant differences among CBN,CBW,and CB treatments.In the P fertilized plots,the order of soil resin-P,Na HCO₃-P,and Na OH-P concentrations under different treatments followed as CBN,CB > CBW > CK.?5?Root weight,RLD,average diameter,surface area,and volume of cotton were significant higher in CB,CBN,and CBW treatments than those in CK treatment.The order of root weight and RLD under cotton biochar amendment treatments followed as CB,CBN > CBW.The the highest average diameter,surface area,and volume of cotton root were found in CBN treatment,and then were in CB treatment,and the lowest were found in CBW treatment.In the P0 plots,biomass and P uptake of cotton were significant higher in CB,CBN,and CBW treatments than in CK treatment,but no significant differences were found among CB,CBN,and CBW treatments.In the P105 plots,the order of cotton biomass and P uptake under different treatments followed as CBN,CB > CBW > CK.Cotton biochar amendment increased significantly P fertilizer use efficiency of cotton.The P fertilizer use efficiency were 127%,120%,and 93%higher in CB,CBN,and CBW treatments than that in CK treatments.[Conclusion] Three types of biochar amendment increase soil N and P concentrations,reduce apparent N loss from soil,and promote cotton growth,nutrient uptake,and yield.Comparison among three types of biochar,poultry manure biochar and cotton straw biochar are obviously better than maize cob biochar.Cotton straw biochar increase soil labile P content and promote root weight and length density of cotton.Hence,biochar can enhance root growth and nutrient uptake,and increased P fertilizer use efficiency.