Study On Forms Of Soil Phosphorus And P Adsorption In Soils Under Long-term Crop Rotation And Fertilization Systems

Phosphorus is one of the necessary nutrients for crop growth, but it is alsonon-renewable mineral resources. Increasing use efficiency of phosphorus fertilizer andcontent of available phosphorus in soil and reducing soil phosphorus leaching and adsorptionof phosphorus are one of the key issues of further development of modern agriculture. Withlong-term experiment, forms of phosphorus, phosphorus sorption parameters in soils, soilphosphorus and soil organic matter under different crop rotation systems in a26a long-termfertilization field experiment in an arid loess plateau were determined for study of effects ofcrop rotation and fertilization on forms and adsorption of the phosphorus in the soil, as well asthe content of soil phosphorus and soil organic matter. The relationships between soilphosphorus adsorption parameters and phosphorus forms were analyzed, and the therelationships between soil phosphorus and soil organic matter(SOM) were also analyzed.Meanwhile, soil P leaching change-point was measured by lab simulation experiment.Relations between part of soil properties and soil phosphorus adsorption parameter orphosphorus leaching change-point were studied, as well as the relationship between soilphosphorus adsorption parameters and phosphorus leaching change-point were studied.Themain conclusions were drawn as follows:The maximum P adsorption capacity(Qm) of the soil was reduced under both long-termcrop rotation and long-term fertilization, and Qm of the soil was reduced by long-termapplication of phosphorus fertilizer(P) and organic fertilizer, but the degree of P sorptionsaturation(DPSS) of the soil was increased, the Qm of M₇₅N₁₂₀P₆₀was reduced by49.92%than CK treatment, but DPSS of M₇₅N₁₂₀P₆₀was increased by21.5times than CK treatment.Relative to other crop rotation and continuous cropping systems, the application of nitrogenand phosphorus fertilizer (N₁₂₀P₆₀) reduced Qm of the soil under the Wheat-Corn-Pea croprotation system, and the Qm of Wheat-Corn-Pea rotation was reduced31.57mg kg^-1thanWheat-Alfalfa rotation. As well as the application of NP plus organic manure (M₇₅N₁₂₀P₆₀)had a similar effect on Qm of the soil under the Wheat-Corn crop rotation system, and the Qm of Wheat-Corn rotation was reduced61.56mg kg^-1than Wheat-CornⅡrotation.Correlation analysis shows that Qm of loess plateau farmland were significantlynegatively related to total phosphorus (T-P),Olsen-P,CaCl₂-P and SOM(P<0.01), andnegatively related to pH(P<0.05). A constant related to bonding energy(k) were positivelyrelated to Olsen-P, but insignificantly to other parameters. The degree of P sorptionsaturation(DPSS) were significantly positively related to T-P,Olsen-P,CaCl₂-P and SOM, butinsignificantly to pH. The maximum buffer capacity (MBC) were significantly positivelyrelated to pH, and significantly negatively related to SOM, negatively related to CaCl₂-P, butinsignificantly to T-P and Olsen-P.In all the rotation systems, long-term application of N₁₂₀P₆₀increased the contents of soilphosphorus and SOM, while the long-term application of NP plus organic manure(M₇₅N₁₂₀P₆₀) significantly increased the contents of soil phosphorus and SOM. In all therotation systems, Wheat-Pea rotation(W-P-R) and Wheat-Corn rotation(W-C-R) had the besteffect on increasing soil phosphorus, the content of T-P and Olsen-P of W-P-R and W-C-Rtreatments was the highest. Under N₁₂₀P₆₀fertilization, content of T-P of them wererespectively increased by22.0%and23.1%than Wheat-Alfalfa rotation(W-A-R) treatment,and content of Olsen-P of them were respectively increased by1.86and1.35times thanW-A-R treatment. Under M₇₅N₁₂₀P₆₀fertilization, content of T-P and Olsen-P of them wererespectively increased by21.0%,22.9%and1.1times,1.0times than Alfalfa continuouscropping(A-C) treatment. Available phosphorus in the soil gradually exhausted after26along-term single application of nitrogen fertilizer(N₁₂₀), its Olsen-P was reduced by13.4%than CK treatment, and reduced by60.5%than before the experiment. Differentcropsforrotations also had certain impact on soil phosphorus and SOM in same rotationsysterm. The correlation analysis shows that SOM was significantly related to T-P,Olsen-Pand CaCl₂-P and extremely significant negative relations to pH.The various forms of phosphorus in the soil were accumulated under long-termfertilization, and the various forms of phosphorus in the soil were also taken a significantchange under long-term crop rotation. After26years of long-term fertilization, compared withthe bare land, the average value of Ca₂-P,Ca₈-P,Al-P,Fe-P,O-P,Ca₁₀-P and organicphosphorus of all crop rotation system were respectively increased by180%,106%,99%,85%,77%,9%and22%under N₁₂₀P₆₀fertilization, and they were respectively increased by832%,215%,105%,95%,96%,12%and37%under M₇₅N₁₂₀P₆₀fertilization. The same infertilization, the Wheat-Corn rotation and Wheat-Pea rotation systems significantly increasedthe contents of various forms of inorganic phosphorus, and the soils were higher in available Punder crop rotation than under long-term continuous cropping, especially in Ca₂-P. Correlation analysis shows that Qm were significantly negatively related to Ca₂-P,Ca₈-P,Fe-P,Ca₁₀-P and organic phosphorus, and negatively related to occluded phosphorus(O-P),but insignificantly to Al-P. DPSS were significantly related to Ca₂-P,Ca₈-P,Ca₁₀-P andorganic phosphorus, and related to Fe-P and O-P, but insignificantly to Al-P. Path analysis andstepwise regression analysis show that among the inorganic phosphorus fractions incalcareous Heilu soil, Ca₂-P contributed the most to Olsen-P.Long-term application of P₆₀,N₁₂₀P₆₀and M₇₅N₁₂₀P₆₀significantly increased the contentsof soil phosphorus, especially the contents of Olsen-P and CaCl₂-P were increased. After26years of long-term fertilization, content of Olsen-P of M₇₅P₆₀and M₇₅N₁₂₀P₆₀treatment wererespectively increased by10.7and9.8times than CK treatment, content of T-P wererespectively increased by60.4%and57.7%than CK treatment and content of CaCl₂-P wererespectively increased by11.4and9.7times than CK treatment. After long-term fertilizing,there was significantly linear correlation between Olsen-P and T-P, but significantlyexponential relation between Olsen-P and CaCl₂-P. Correlation analysis shows that theleaching change-point of soil Olsen-P had very significant positive correlation with Qm, andhad significant positive correlation with MBC, while it was significantly negatively related toDPSS,Olsen-P,T-P and CaCl₂-P. Results also indicated the value of soil Olsen-P leachingchange-point of loess soil arid land was about55mg kg^-1, and coincided with DPSS15%value,namely, the value of DPSS15%can be taken as soil Olsen-P leaching change-point of thepresent study area.