Effects Of Long-term Fertilization And Management On Soil Enzyme Activity Of Lou Soil

Phosphorus is one of the essential nutrients for plant growth, which occurs in the soilswith various chemical forms. Different land use and fertilizer managements might have agreat influence on its speciation transformation, content, biological availability. It has greatscientific significance to understand the effects of soil management strategies as well asfertilizer management regimes on soil phosphorus fraction. By employing inorganicphosphorus （IP） fractionation method proposed by Jiang and Gu, and Tiessen, we investigatedthe effects of land use and fertilizer management regimes on the phosphorus fraction in amanural loess soil of a20-year long-term experiment. Treatments include bare fallow withoutvegetation （Fallow） and cropland abandonment （Setaside） under rainfed and irrigatedconditions, and such the nutrient management practices as un-a mended control （CK）, N, NK,NP, PK, NPK, straw plus NPK （SNPK） and2rates of manure plus NPK （M1NPK andM2NPK） for wheat-maize cropping system under irrigated, and seven fertilizer treatments forwinter wheat-summer fallow system under rainfed conditions. The results showed that Ca-Pwas a dominant fraction of the inorganic phosphorus in calcareous soil, occupied73.9%oftotal inorganic P; followed by O-P, accounted for17.16%; the content of Al-P and Fe-P waslow and cognate, occupied4.69%and4.98%of the total inorganic P, respectively. Thecontent of soil total inorganic phosphorus remained constant in treatment of Fallow andSetaside, whereas a significant change was observed for the proportion of inorganic fractionsto total IP. Ca₂-P, Al-P and Fe-P were found to be the main source of P for vegetation grownon plot of Setaside. In contrast, the content of soil total inorganic phosphorus was reducedsignificantly in control, where Ca₂-P, Al-P and O-P were showed to be the main contributorof P to crop production. The content of total inorganic phosphorus and its fraction wasincreased significantly on plots those receiving P containing fertilizers/manure over20years,of which Ca₂-P and Ca₈-P gained much more. Long-term application of P containing fertilizeralso promoted transformation of Ca10-P into other forms, and thus reduced the phosphorusfixation.In wheat-maize rotation cropping system with irrigation, long-term fertilizer P addition,notably manure in combination with mineral NPK, increased the contents of soil IP and its fractions, The order of increment was Ca₂-P> Ca₈-P> Al-P> Fe-P> O-P> Ca10-P.Accumulated phosphorus existed mainly in the form of Ca₂-P and Ca₈-P in the soil. SoilCa10-P content remained unchanged after fertilizer P application while its percentage relativeto Pi declined dramatically. On plot receiving no fertilizer, soil occluded phosphorus wasobserved playing a important role in crop growth.Based on Tiessen phosphorus fractionation system, the total P of the studied soil wasmainly made up of Pi, it stood65.76%-79.30%of the total phosphorus; the organicphosphorus was only20.70%³4.24%. According to the activity of the phosphorus, themoderately labile phosphorus （NaOH-P, HCl-P） was the mail fraction of TP,accounted for69.28%of the TP, followed by Residual phosphorus, consisted22.42%of TP, the content oflabile phosphorus （Resin-P, NaHCO3-P）was the lowest,only had8.35%of TP. All thetreatments were showed a tendency of increasing inorganic phosphorus, and reducing organicphosphorus. As compared to the corresponding value in soil sampled prior to experiment, thecontent of HCl-P and Resideal-P was reduced significantly on Fallow and setaside plots, andNaOH-P was increased, while labile P has no change. Twenty years cropping withoutphosphorus application had no significant effects on moderately labile and stable phosphorus,but reduced labile P significantly. Application of P fertilizer significantly increased labile andmoderately labile phosphorus contents, reduced stable phosphorus contents.