| Phosphorus（P）is an essential macronutrient for crop growth and production.The widespread application of chemical P fertilizers over the last decades increased the risk of P loss and eutrophication.Animal manure can be used as nutrients resource to cut down the agricultural waste,reduce the application of chemical fertilizer,and therefore alleviate environmental risks.However,the effect of manure on soil P availability depends on manure types,application rates,soil types,and farmland utilization patterns.Therefore,it is important to explore the mechanisms of P release rates from different manures and also P transformation in flooded and upland soils after the input of manures.Our aim is to understand the soil P cycle in drying-wetting rotation under the application of organic manures for the efficient utilization of P in agriculture.In this study,both incubation experiments and field experiments were conducted.The water-extractable P in different types of animal manures（PM,pig manure;CM,chicken manure;DM,dairy manure;OM,conventional commercial organic compost）were analyzed and P fractions in soil were extracted according to Hedley method.Po classification,13C-NMR,PLFA,etc were applied to analyze the change of P availability in paddy soil,the transformation of soil P fractions,the response of biological factors such as microbial community,and extracellular enzyme activity in drying-wetting alternating soil after the input of organic manures.In addition,organic P（Po）mineralization,microbial community,enzyme activity,and P composition were analyzed for their correlation to P availability.Our study will provide a therotic reference for the application of animal manure in agriculture practice.The main results were as follows:（1）By analyzing the Water-Extractable P（WEP）released from different manures with time,it was found that WEP released from commercial organic compost after 7 days of hydroponics accounted for 31.6%of total P（TP）,followed by pig manure（20.5%）,chicken manure（16.2%）,and dairy manure（0.3%）.All the application amounts of different manures（calculated as Pi amounts for LP,low P;MP,medium P;and HP,high P）after 120 days significantly（P<0.05）increased soil available P（Olsen-P）,but the difference between each treatment was not significant.Therefore,low P addition(60 kg P2O5 ha-1)is recommended in the following experiments.The Olsen-P released or amount after the addition of OM,PM,CM,and DM average increased by 32.7%,26.1%,12.4%,and 10.4%,respectively,in comparison with the control(120th).Analysis of the soil P fractions indicated that,under flooded conditions,PM treatment significantly（P<0.05）increased soil available P by 29.1%compared to the control,while under upland conditions(120th),PM treatment significantly（P<0.05）increased moderately inorganic P by 17.1%.Using structural equation modeling（SEM）analysis,it was found that the addition of manure prefer to transformation of Na OH-Pi to Na HCO3-Pi.In conclusion,WEP concentration was highest in pig manure and commercial organic compost.In addition,all the manures,especially the pig manure（PM）can improve the amount or release rate of Olsen-P in soil,which in turn increases the available P components in paddy soil.Pig manure could promote the transformation of moderately inorganic P to available P.（2）Field experiments with application of different manures in rice-wheat rotation were conducted to investigate soil P fractions,soil microbial biomass,and runoff of total phosphorus（TP）for two years.30%of chemical P fertilizer was substituted by animal manures to explore the soil P transformation in the rice-wheat rotation soils.The results showed that substitution of different organic manures（PM,CM,and DM）didn’t reduce the yield of rice or wheat,but significantly（P<0.05）reduced soil total P loss due to the runoff by 3.2%,compared with chemical P fertilizer treatment.PM and CM application significantly（P<0.05）increased the soil available P by 37.4%and 58.5%compared to the control.Furthermore,animal manures significantly（P<0.05）increased soil microbial biomass carbon（MBC）by 11.3～18.4%and microbial biomass P（MBP）by 57.1～81.2%.SEM analysis indicated that manures promoted the transformation of moderately available P to available P.Microbial biomass and microbial metrology play an important role in the transformation of soil P,especially the transformation of organic P（Po）to available P due to the increase of soil microbial biomass and changing the microbial biomass stoichiometric ratio.（3）The biological mechanism of soil P transformation was further explored through incubation experiments.Compared to the control(30th),animal manures（PM,CM,and DM）significantly（P<0.05）increased soil available P and Po by 2.7～14.7%and 6.4～20.0%respectively,amongst which PM treatment had the strongest effect.In addition,manure treatments also significantly（P<0.05）increased MBC and MBP by 10.4～14.0%and51.9～57.8%.PM,CM and DM increased bacterial abundance by 34.8%,22.5%and 33.5%,respectively.The PM treatment significantly（P<0.05）increased bacteria biomass to 561μg g-1.Overall,during the early stage of incubation,microorganisms were affected by the P source,while the C source was the main regulator for microbial growth during the later stage.Redundancy analysis showed that soil MBC/MBP ratio was the main factor involved in the transformation of soil available P and moderately inorganic P.In summary,animal manures（especially pig manure）promote bacterial abundance by providing C source,thereby modified the microbial community and microbial biomass,adjusted the microbial biomass ratio,and promoted the transformation of moderately inorganic P and Po to available P.（4）According to the above research results,pig manure was selected as the research object,focusing on the transformation mechanism and main regulatory factors of Po in drying-wetting alternate soil affected by pig manure application.The results showed that PM treatment significantly（P<0.05）increased soil Olsen-P by 476%compared to the control（CK）.Under the flooded conditions,PM significantly（P<0.05）increased MLPo and HAPo by 38.2%and 429%,respectively.While PM significantly（P<0.05）reduced the HAPo by71.3%.PM treatment enhanced extracellular enzyme activities under wet-dry conditions.Compared to CK,PM treatment significantly（P<0.05）increased the L-leucine aminopeptidase（LAP）and alkaline phosphatase（ALP）under flooded conditions by 10.2%and 8.6%,respectively.β-1,4-glucosidase（BG）,β-D-cellobiosidase（CBH）and L-leucine aminopeptidase（LAP）activities were increased by 33.3%,18.1%,and 15.0%,respectively.Through vector analysis it was found that the soil microorganisms were mainly limited by P sources,followed by C sources.Microbial carbon limitation was enhanced by P limitation,indicating that manure could alleviate P and C limitations to promote soil microbial growth.Compared to flooded conditions,drying process of soil increased the abundance of Actinobacteria and Acidobacteria in soil bacterial communities.Actinobacteria and Acidobacteria were positively correlated with ALP.Through random forest model analysis,the results showed that the main predictors of soil Po and Olsen-P were CO2 accumulation,WHC,and P application.In conclusion,animal manures can stimulate the abundance of oligotrophic microorganisms（Actinobacteria and Acidobacteria）by modification of soil nutrients（including TC and TP）,and promote the release of ALP,which accelerates the transformation of Po to available P.In conclusion,on the premise of ensuring crop yield and not increasing the soil runoff TP concentration,animal manure application changed the structure of soil microbial community,improved soil microbial activity,stimulated the increase of specific microbial community and the secretion of ALP,and finally accelerated the transformation of soil moderately labile P and Po into labile P.Based on incubation combined with field experiments,this study measured and analyzed animal manure types,microbial communities,enzyme activity measurement,P components and bio-available P,which provided theoretical basis for guiding scientific application of organic fertilizer to improve soil P availability and reduce environmental load. |
