Evolution Of Soil Phosphorus Fertility And Phosphate Fertilizer Efficiency Of Paddy Soils In The Upper And Middle Reaches Of The Yangtze River Based On Several Stationary Experiments

Phosphorus(P)is one of the essential nutrients for plant growth and development.The importance of P inputs becomes more prominent for paddy field in southern China as the general lack of P.But the phenomenon of P deficiency in the soil will be significantly improved with the long-term application of fertilizer.The reasonable application of phosphate fertilizer to achieve food security and environmental friendliness must be based on the effective regulation of soil P fertility.This research was based on 5 experimental sites in the middle and upper reaches of the Yangtze river.Several treatments were examined:applying chemical P plus manure(i.e.NPM?NPKM?NPKS?PKM),chemical P(i.e.NP?NPK),and without chemical P(i.e.CK?M?NK?NKM).Through analysis the evolution characteristics and influencing factors of soil total P,available P,P balance rate and crop P uptake,P recovery rate,the utilization ratio of phosphate fertilizer,phosphate fertilizer agronomic efficiency and physiological efficiency by 21-31 years long-term experiments,to clarify the characteristics of soil P pool and P fertilizer efficiency under long-term fertilization in a region.It was great theoretical and practical significance to improve the utilization efficiency of phosphate fertilizer for reasonable application of P fertilizer and to sustain agriculture development.The main finds as follows:1,The yield of early rice and late rice from NPKM and NPKS treatments could be increased by 1.1%-19.6%and 5.7%-21.6%compared with NPK,respectively.The yield of rice and wheat could be increased by application of chemical P fertilizer significantly.The contribution ratio of P fertilizer for early rice was larger than that for late rice in the regions with double rice cropping.The contribution ratio of P fertilizer for wheat season was larger than that for rice season in the regions with wheat-rice rotation.2,The total P,available P,and P activation coefficient(PAC)increased by application of P fertilizer in all sites.The annual mean value of available P content and PAC for each experimental site under long term fertilization performanced following the order:NPM,NPKM,NPKS,PKM>NP,NPK>CK,M,NK,NKM.There was a significant positive correlation between soil PAC and soil organic carbon content.The rate of soil available P increased in purple soil and paddy soil was 0.8-2.4 and 0.2-2.8 mg/kg·y respectively.The PAC in rice wheat rotation system and in double rice system was increased 0.18%and 0.16%with the increase of soil organic carbon in 1.0 g/kg,respectively3,The natural supply of P in different sites was significantly decreased with time,and the annual decrease rate of phosphorus natural supply in purple soil and red paddy soil ranged from 0.48 to 0.63 kg/hm~2.The balanced application of fertilizer can promote the P uptake by crops,and P uptake by early rice was greater than that by late rice.The recovery rate of P fertilizer was decreased with the increase in the application amount of P fertilizer significantly.The recovery rate of P fertilizer was decreased by~9.5%with an increase rate of P fertilizer application of 10 kg P/hm~2.The effects of different fertilization on fertilizer agronomic efficiency of each site was insignificant.The P content of the soil at each site was surplus with the long term input of P fertilizer.The recruitment of Olsen-P was significantly correlated with P surplus,and that the P surplus of soil ranged within a certain range.The soil available P content under application of chemical P fertilizer could be increased more than that under the organic P fertilizer when surplus equal P in soil.4,The agronomic thresholds of soil available P for wheat and rice was 16.6 and 10.2mg/kg in purple soil respectively,and the agronomic thresholds of soil available P for rice was 17.4 mg/kg in double rice cropping system in red paddy soil.It will take about 3-21years to reach agronomic thresholds for soil available P content by reasonable fertilization practices(NPK and NPKM)for experimental sites.In addition,there was a significant positive correlation between soil available P and average P uptake.5,The total amount of inorganic P in red paddy soil increased with the fertilization duration significantly.The total amount of inorganic P in the treatment of combination of organic and inorganic fertilizer was significantly higher than that in the treatments with chemical fertilizer or organic manure alone.The annual change rate of Fe-P was the fastest among the inorganic phosphorus fractions,with an average annual increase of about 1-8mg/kg,and the annual change rate of inorganic P in Ca-P was the slowest,with an average annual increase of about 0.3-2.0 mg/kg.The contribution of Fe-P and Al-P on the content of available P in red paddy soil more than other inorganic P fractions(Ca-P and O-P).There is no affect for the proportion of total inorganic P to total P under long-term application of chemical fertilizer.Applying fertilizer increased the proportion of O-P mainly,and decreased the proportion of Al-P,especially after the application of chemical P fertilizer or chemical P fertilizer combine with organic fertilizer.