Reasonable nutrient and water management is effective ways to improve productivity and biodiversity of degraded grasslands. However, little is known about the effects of nutrient and water addition on soil inorganic phosphorus (P) fractions in old-field grasslands. Based on a field experiment with nutrient addition (N: 10 g·m-2·a-1, P: 10 g·m-2·a -1) and water addition (180 mm water irrigated during plant growing season) in Duolun County, Inner Mongolia in 2005, we examined the changes of inorganic P fractions and Olsen-P contents in the topsoil (0-10 cm). Results showed that 11-year P addition significantly increased total inorganic P (TIP) content, and that exogenous P was mostly transformed into calcium phosphate (Ca-P: 62.6%-69.2%), and then into aluminium phosphate (Al-P: 19.9%-25.1%), ferric phosphate (Fe-P) and occluded P (O-P). Phosphorus incorporated with nitrogen (N) addition significantly increased Fe-P and Al-P contents by declining soil pH and activating Fe3+ and Al3+ in soil. Water addition alone significantly increased Fe-P, Al-P, and decalcium phosphate (Ca10-P) fractions, and the contents of Fe-P, Al-P, octacalcium phosphate (Ca8-P), and Ca10-P were greater in P incorporated with water treatment than in P addition alone. There was no difference of each inorganic P fraction between P incorporated with N and water treatment and P incorporated with N treatment. Phosphorus and P incorporated with N additions significantly increased soil Olsen-P content, while water addition significantly decreased soil Olsen-P content under P addition alone and P incorporated with N treatment. In the calcareous soils, calcium superphosphate addition could enhance soil inorganic P pool through increasing Ca-P fraction.
合理的养分和水分管理措施是提高退化草地生产力和生物多样性的有效途径,但养分和水添加对弃耕草地土壤无机磷组分的影响研究较少。本文依托内蒙古多伦县2005年建立的养分(N: 10 g·m-2·a-1、P: 10 g·m-2·a-1)和水分(植物生长季增水180 mm)添加田间试验,研究了表土(0～10 cm)无机磷组分及有效磷(Olsen-P)含量。结果表明: 11年的磷添加显著增加了表土无机磷总量,外源磷大部分转化为磷酸钙(Ca-P: 62.6%～69.2%),其次是磷酸铝(Al-P: 19.9%～25.1%)、磷酸铁(Fe-P)和闭蓄态磷(O-P)。磷氮添加通过降低土壤pH、促进Fe3+、Al3+活化而显著增加Fe-P和Al-P的含量。单独增水显著增加Fe-P、Al-P、磷酸十钙(Ca10-P)含量;磷水处理的Fe-P、Al-P、磷酸八钙(Ca8-P)、Ca10-P含量均显著高于单独加磷处理,而磷氮水与磷氮处理间土壤各组分无机磷含量均无显著差异。磷及氮磷添加处理显著增加了土壤Olsen-P含量,但磷及氮磷处理在增水条件下土壤Olsen-P含量显著降低。石灰性土壤中,过磷酸钙添加主要通过增加Ca-P组分来增加土壤无机磷库。.
Keywords: inorganic P fraction; nitrogen; old-filed grassland; phosphorus; precipitation.