Effects Of Organic Amendments On Soil Phosphorus Adsorption And Related Factors In Reddish Paddy Soils

Phosphorus?P?is one of the essential nutrient elements in the growth of crops.Phosphorus in soil mostly exists in poorly soluble or adsorptive state and is poor movable.However,with the extensive application of phosphate fertilizer,or organic amendments based on crop nitrogen demand will lead to excessive accumulation of P in soil and increase mobility,resulting in agricultural non-point source pollution and eutrophication of water body.To systematically evaluate the effects of organic amendments on the agro-chemical effects?i.e.,P availability?and environmental effects of P in reddish paddy soils,this study was based on the long-term fertilization experiment?since 1981?,in Jiangxi province representative reddish paddy soil as the research object,using soil test P?Olsen-P,Bray1-P,iron strip extractable P[Fe-strip-P],resin strip extractable P[Resin-P]?and P isothermal adsorption experiment,studied the effects of long-term different organic amendments on soil P availability and soil P adsorption properties.Meanwhile,the effects of biochar on the P adsorption and desorption properties of reddish paddy soil were studied by means of culture experiment.The main study results are as follows:1.Fertilization,especially chemical fertilizer combined with organic fertilizers such as Chinese milk vetch?A.sinicus L.?and biogas slurry,significantly increased the available P content of paddy soil Olsen-P,Bray1-P,Fe-strip-P and Resin-P.Under the same fertilization mode,Bray1-P had great difference in two years,and was more sensitive to the change of available P content in paddy soil.The variation coefficient of Olsen-P in two years was smaller than the other three methods,and the accuracy was higher than the other three methods.The four methods for determining available P in paddy soils showed significant correlation in two years.For the reddish paddy soil under different fertilization modes,four methods could be substituted for each other.There was a linear relationship between the P uptake of rice plants and the four methods for determining the available P content in paddy soils.With the increase of available P in soil,the P uptake by plants also increased.Compared with Fe-strip-P,Olsen-P,Bray1-P and Resin-P had higher correlation with P uptake in rice,which could reflect the P supply capacity of reddish paddy soil in Jiangxi province.2.In the P sorption isotherm experiment,the amount of sorbed P increased with initial added P concentration increasing.The Langmuir equation was more ideal than Freundlich and Temkin equations in fitting the P sorption isotherm,which had determination coefficients greater than 0.99 for all treatments.Biogas slurry incorporation had the greatest Langmuir P sorption maximum?X_m?,which was significantly higher than the other three treatments?p<0.05?,followed by straw retention and chemical fertilization treatments,and the lowest in CK.In addition,biogas manure treatment had the highest value of degree of P saturation.However,there were no significant differences in the constant related to the bonding strength and maximum buffer capacity among the four treatments.Oxalate-extracted Fe,Al,and P?Fe-ox,Al-ox,and P-ox,respectively?,and Mehlich 3-extracted Ca and Mg?Ca-M3 and Mg-M3?were positively correlated with X_m,especially for P-ox and Fe-ox,for which the correlation coefficient was 0.95?p<0.01?and0.64?p<0.05?,respectively.Principal component analysis showed that Fe-ox,Al-ox,Ca-M3 and Mg-M3 contributed mostlybiochar to the variation of P sorption characteristics among the four fertilization regimes.Compared with CK and chemical fertilizer application treatments,long-term incorporation of biogas manure increased the contents of amorphous Fe and Al minerals in paddy soil,and thus enhanced soil P sorption capacity.3.In the biochar culture test,high P soil and low P soil with different biochar were added.With the increase of P concentration,the amount of P adsorption increased gradually.The fitting coefficient of Langmuir and Freundlich equation to the adsorption curve of P isothermal adsorption of different biochar soils was above 0.9,and the fitting effect was good.Based on the Langmuir equation,the maximum P uptake?X_m?and P zero holding equilibrium concentration?EPC₀?of low P soil were higher than that of high P soil after adding biochar,and X_m and EPC₀ were significantly different in soil phosphorus fertility.Based on the Freundlich equation,the adsorption of soil on P was that the high P soil was larger than the low P soil,and which on the soil phosphorus fertility and biochar materials were significantly different.The two equation parameters showed that the adsorption of soil to P was affected by soil phosphorus fertility and biochar materials.After adding different biochar,the adsorption amount of low P soil and high P soil increased,desorption rate increases.When the concentration was low,it was mainly adsorbed,desorption and desorption rates were small.With the increase of P concentration,desorption and desorption rates increased rapidly.