[Effects of nutrient and water addition on soil inorganic phosphorus fractions in an old-field grassland]. / å »åˆ†å’Œæ°´æ·»åŠ å¯¹å¼ƒè€•è‰åœ°åœŸå£¤æ— æœºç£·ç»„åˆ†çš„å½±å“.

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.

[Distribution characteristics of soil phosphorus in maize belt farmlands of Northeast China].

The study on the vertical distribution and latitudinal differentiation of soil total and organic phosphorus (P) down to 100 cm depth in maize belt farmlands of Northeast China showed that in Hailun and Harbin of Heilongjiang Province, Gongzhuling of Jilin Province, and Dashiqiao of Liaoning Province, soil total P decreased with soil depth, being significant higher in 0-40 cm than in 40-100 cm (P < 0.01). In Dehui of Jilin Province and in Changtu and Shenyang of Liaoning Province, soil total P was relatively lower in 40-60 cm, but no significant difference was observed among different layers. Soil organic P was significantly higher in 0-20 cm than below 20 cm (P < 0.05). Soil total and organic P increased with increasing latitude (P < 0.05). The differences in climate conditions and soil types were considered as the main reasons induced the latitudinal differentiation of soil P. Soil total and organic P were significantly correlated with soil organic carbon (P < 0.01), indicating that soil organic matter was one of the most important factors affecting the soil P content and its distribution in maize belt farmlands of Northeast China.