Soil Carbon,Nitrogen And Phosphorus Stoichiometry,and Phosphorus Balance Under Long-term Fertilization In Different Paddy Soils

Understanding the nutrient stoichiometry and their balance is very important for a sustainable agricultural production system,specially under the long-term different organic and inorganic fertilization in rice based cropping systems.Soil carbon?C?,nitrogen?N?and phosphorus?P?are major essential nutrient elements,which play significant role in plant growth and agricultural pollution.Therefore,investigating soil C:N:P stoichiometry and P balance under long-term fertilization is very important to maintain sustainable crop production.The main objectives of present study were to investigate the effect of different long-term fertilization on ecoenzymatic stoichiometry and P dynamics in paddy soil.To investigate the relationships between soil C:N:P stoichiometry and P fractions in paddy soil,and to investigate the microbial community structural response to the soil C:N:P and microbial biomass stoichiometry under long-term fertilization in rice-based cropping system.In present study we selected long-term different organic and inorganic fertilization treatments in the rice based cropping systems at the five different long-term experimental sites in the southern region of China.Treatments of long-term experiment at the Chongqing?started from 1991?and the Suining?started from 1981?sites included CK?no fertilization?,NPK?N,P and potassium fertilization?and NPKM?N,P,K and manure application?.In the two other long-term experimental sites both located in Hefei city?started from 2013 and 2015 named as HF-1 and HF-2,respectively?,Anhui province of China,treatments included,CK,NPK,NPKS?NPK plus straw?and NPKM treatments.At the Qiyang experimental site?started from 1982?treatments included,CK,NPK,NPM,NKM,PKM and M treatments.Results showed that inorganic fertilization significantly decreased soil pH,compared to the combined organic plus inorganic fertilization or manure application alone at the all experimental sites.Soil enzyme activities and nutrient availability were also higher under the combined manure plus inorganic fertilization treatments,compared to the inorganic fertilization at the Chongqing and Suining experimental sites.Compared to the CK treatment,the NPK and NPKM treatments significantly decreased soil C:N,C:P and N:P ratios at Chongqing and Suining sites.Compared to the inorganic fertilization,NPKM treatment significantly decreased residual-P fraction by 61.6%and 14.0%at Chongqing and Suining sites,respectively.In contrast,non-labile fractions were decreased in manure treatments.Moreover,path analysis indicated that indicated that soil C:N:P stoichiometry controlled P uptake by affecting P transformation from non-labile to labile-P pools.At the both experimental sites of Hefei,NPKS and NPKM treatments,increased the grain yield,P use efficiency?PUE?and decreased P balance,compared to the NPK treatment.Compared to the CK treatment,crop yield under the NPKM and NPKS treatments was increased by 110%and 115%,respectively at HF-1and 100%and 122%,respectively at HF-2 site.Compared to the NPK treatment,NPKS and NPKM treatments,increased soil pH and SOC content in surface?0-20cm?and subsurface?20-40cm?soil layer.NPKM and NPKS treatments,increased labile fractions of P and decreased residual P content,compared to the NPK treatment.At the Qiyang experimental site,results showed that combined application of manure and inorganic fertilizers significantly increased soil C,N,P contents,extracellular enzyme activities and total phospholipid fatty acid?PLFA?concentration,compared to CK and NPK treatments.Compared to the CK treatment,?-1,4 glucosidase,?-1,4 glucosidase,urease,Acid phosphomonoesterase and phosphodiesterase activities under the NPKM treatment were increased by 23.0%,279%,118.3%,62.3%and 71.9%,respectively.At the Qiyang site,we also found that soil C:N showed positive?P<0.01?relationship and soil C:P ratio showed negative?P<0.05?relationship with microbial C:N and C:P ratios,respectively.The order of individual PLFAs concentrations was:Gram negative bacteria>Gram positive bacteria>Actinomycetes>AM fungi>Fungi>Eukaryotes>anaerobes in the all fertilization treatments.At Qiyang site,crop yield and sustainability yield index under combined application of manure and chemical fertilizers was significantly higher than chemical fertilization.Soil organic C sequestration rates under NPM,NKM,PKM and NPKM treatments were increased,while decreased under CK and NPK over the fertilization years.At the Qiyang site,P balance was exceeded the environmental risk threshold(P balance>49 kg hm^-2 year^-1)under combined application of chemical P fertilizer and manure,which may pose a serious threat to the aquatic environment.Boosted regression tree indicated that soil available N?AN?,organic carbon?SOC?and total N?TN?were the most influencing factors of crop yield and their relative influence on crop yield was 36.4%,17.8%and 13.4%,respectively.Overall we concluded that combined application of manure and inorganic fertilizers significantly increased the crop yield and nutrients availability,compared to the inorganic fertilization.Combined application of manure and inorganic fertilizers also increased soil pH and SOC content,compared the inorganic fertilization at different experimental sites.Long-term application of manure increased the labile fractions of P and decreased the residual-P.Soil C:N:P stoichiometry indirectly controlled P uptake by directly affecting P transformation from non-labile to labile-P pools.However,at Qiyang site,long-term combined organic and inorganic P input under NPKM treatment,the P balance was exceeded the environmental threshold level.The P input under the combined manure and inorganic P application should be reduced to avoid the risk of environmental pollution under long-term fertilization in rice based cropping system.Moreover,ecoenzymatic stoichiometry and microbial community structure were also very sensitive to combined long-term organic and inorganic fertilization that can affect the nutrient acquisition and cycling in agroecosystem.Further research is required to investigate the nutrient stoichiometry at molecular level and microbial nutrient stoichiometry at cellular level to find out the mechanism and controlling factors of ecoenzymatic stoichiometry agricultural production system.Advance research is required to investigate the biochemical and environmental factors that affect the P cycling in soil-plant system in long-term cropping,using high throughput gene sequencing,NMR and XANES techniques.