Effects Of Biogas Slurry And Biochar Applications On Soil Nitrogenand Phosphorus In The Poplar Plantation In A Costal Area,China

Biogas slurry is a kind of high-quality liquid available fertilizer,rich in N,P,K and other nutrients,which can be directly absorbed by plants.Biochar can adsorb nutrients in the biogas slurry and act as a retainer of effective nutrients,reduce leaching of nutrients,and allow the retained nutrients to have a certain hysteresis effect,slow release of effective nutrients retained,and increase nutrient utilization.In this study,the joint application of biogas slurry and biochar in the plantations of a coastal area with low organic matter content and poor water retention and fertility maintenance may improve the soil fertility.In this experiment,a randomized block design was adopted in the poplar plantation in the northern Jiangsu Province,and four biogas slurry application levels were set up,which were CK(0m^3.hm^-2.a^-1),L(125m^3.hm^-2.a^-1),M(250m^3.hm^-2.a^-1),H(375 m³·hm^-2·a^-1),respectively,and the four biochar application levels were CK(0t.hm^-2),L(40t.hm^-2),M(80t.hm^-2)and H(120t.hm^-2),respectively.The changes of soil N and P concentrations under different concentrations of biogas slurry and biochar application levels were the main research priorities.The results showed that:?1?Application of biogas slurry significantly increased soil TN,NO₃^--N,NH⁴⁺-N,TP,available phosphorus,MBN,MBP,phosphatase,urease,nitrate reductase,nitrite reductase.NO₃^--N,NH4+-N and MBP reached the maximum under the treatment of medium-strength biogas slurry.Soil TP,available phosphorus,phosphatase,and urease showed H>M>L>CK.Nitrate reductase activity and nitrite reductase activity increased firstly,then decreased,then decreased first and then increased with the increase of biogas slurry application amount.Application of biogas slurry reduced soil pH and MBC,and decreased with increasing biogas slurry application concentration.Soil TN,NH₄⁺-N,and MBC were evenly distributed between the two soil layers,and the soil layer was not significantly different.The other indicators were significantly different among the soil layers.?2?Application of biochar increased soil NO₃^--N,NH₄⁺-N,available phosphorus,MBC,MBN,and MBP,significantly increased soil phosphatase,urease,and nitrite reductase activities,and significantly increased soil pH.Biochar application increased soil TN and TP content but was not significant.Soil TN,NO₃^--N,phosphatase,urease,nitrite reductase reached the highest under high-concentration biochar treatment.The pH,TP,and TN were distributed evenly among the soil layers and the difference was not significant.The other indicators were significantly different among the soil layers.?3?Combined application of biogas slurry and biochar increased soil TN,NO₃^--N,,pH,TP,available P,microbial biomass and enzyme activity,and reduced soil NH₄⁺-N.The effects of combined application of biogas slurry and biochar on soil N and P elements,soil microbial biomass and soil enzyme activity were better than those of single biogas slurry and single biochar application,and there were significant differences between soil layers.?4?The seasonal variation of soil TN content in biochar and biogas slurry was roughly the highest in September,followed by December and June,and lowest in March.The seasonal dynamic change of soil total phosphorus content was December>September>June>March.The content of soil available P,NH₄⁺-N and NO₃^--N,and enzyme activity were generally high in June and September and less in March and December.In short,as a high-quality,quick-acting organic fertilizer,biogas slurry can significantly increase soil N,P and other nutrient contents,and the biochar adsorption characteristics can effectively compensate for the shortcomings of biogas slurry nutrient loss and improve soil nutrient utilization.The effect of combined application of biogas slurry and biochar was better than that of biogas slurry and biochar alone,and it had a significant effect on increasing soil N and P nutrients.