| Soil legacy phosphorus(P)is a huge kind of resource for nutrient supply.P activators can increase legacy P availability by accelerating the transformation of P fractions in P deficient soils.The aim of this study was to examine the role of four P activators(oxalic acid,lignin,phytase and ascorbic acid)in mobilizing legacy P in calcareous wheat soils.Machikou wheat soil with lower available P content(LAPS)was naturally planted,while Shangzhuang wheat soil with higher available P content(HAPS)was carefully managed.A 90-day laboratory incubation experiment was set up for two kinds of wheat soils which were different in legacy P contents and fractions.Then,mixed P activators(oxalic acid+lignin,phytase+ascorbic acid,oxalic acid+lignin+phytase,oxalic acid+lignin+phytase+ascorbic acid)were also added to enhance P availability in two wheat soils.Based on this,XRD,FT-IR,31P-NMR were used to explore the mechanism that P activators transform P fractions and activate soil P.The results proved that the release of available P reached the peak around day 10.This study demonstrated that oxalic acid,lignin,phytase and ascorbic acid all had effects on legacy P transformation,but they targeted different P fractions.The main sources of available P were H2O-P,NaHCO3-Pi and NaOH-Pi which transformed from HCl-P and Residual-P.Oxalic acid mainly decreased the content of HCl-P to improve the content of labile P,which includes H2O-P,NaHCO3-Pi and NaHCO3-Po.Lignin could decrease NaOH-Pi and HCl-P content and also made Residual-P content decline slightly when H2O-P and NaHCO3-P increased.While,phytase and ascorbic acid chiefly worked on organic P.Under their influence,NaOH-Po and Residual-P content decreased,while NaHCO3-Po content increased.Our results showed that oxalic acid and lignin had better effects to improve P availability in both two wheat soils since the content of labile P greatly increased.Under the effect of oxalic acid and lignin,the content of available P increased by 110.7%?419.7%and 4.1%?122.4%respectively.P activators have good potential to utilize the legacy P in agricultural soils.As for the mixed P activators,in LAPS,oxalic acid+lignin+phytase+ascorbic acid had the best activation effect,the P availability activation rate of which was 529%.While,in HAPS,oxalic acid+lignin had the best effect and the P availability activation rate was 529%.In LAPS,mixed P activators had the better effect than single P activators,however,in HAPS,the fact was just the opposite.The effect of P activators was related to the characteristics of soils,so the effect of mixed P activators was not always better than the single P activators.Under the influence of oxalic acid,minerals in soil with larger particle size gradually transformed into clay minerals with smaller particle size.And as for clay minerals,the content of illite,kaolinite and chlorite all decreased.Illite and chlorite would increase the content of available P by releasing the adsorbed P in soil.Through FT-IR and 3 P-NMR,the content of orthophosphate increased.After adding oxalic acid into soil,organic P could be transformed into inorganic P and inorganic P also would increase its availability.The possible mechanism of oxalic acid activating P was to enhance the release of adsorbed P and dissolute stable P into available P. |
PDF Full Text Request