The Spatial-Temporal Variation Of Nitrogen And Phosphotus On Facilities Cultivated Land In Ledu Of Qinghai

Excessive application of fertilizers is very common in vegetable production, which brings the problem of nutrients accumulation in soil,especially in the facilities vegetable cultivated soils. It will lead to lower efficiency and accumulation and leaching of nitrogen and phosphorus if application rates are overdose, moreover the groundwater may also polluted by leaching. In this study, the physiochemical properties and NP content of facilities vegetables soil were collected and combined with field investigation in Ledu County, Qinghai Province, China. The chemical properties and N, P content of facilities vegetable cultivated soils were determined at laboratory. Results as follows:1. The amount of alkali-hydro nitrogen, total nitrogen and organic matter in soils (0-20cm) were increased with the cultivated years of facilities vegetable cultivation; while soil pH declined with the increase of cultivation years. There is a significant positive correlation between soil salts content and cultivated years.2. Soil nitrate and ammonium content were increased with the cultivated years of facilities vegetables cultivation. In soil surface (0-20cm), nitrate and ammonium have an accumulation process under 20 cm layers and their contents have a little change. Nitrate larger share of mineral nitrogen, achieved 94.24%, while ammonium only account for 5.76%. So nitrate is the main form of nitrogen for crops to absorb and utilize. In 0-20cm facilities vegetables cultivated soils nitrate content activity significantly positive correlated with total salt and soil pH. That indicates total salt increased while the soil pH decreased as excessive application of fertilizers.3. The contents of total phosphorus, available phosphorus, inorganic phosphorus and organic phosphorus were increased with the cultivated years of facilities vegetables cultivation, and decreased with facilities vegetables cultivated soil depth increase. Different forms of phosphorus in cultivated soil enriched in surface soil. Inorganic P is the main form of phosphorus in facilities vegetables cultivated soil. It account for 65.85% of total phosphorus. Proportion of Ca₂– P, Al– P, O - P increased, while Ca8– P, Fe– P, Ca10– P decreased with the cultivated years of facilities vegetables cultivation. Proportion of Ca₂-P, Ca8-P, Al-P, Fe-P decreased and Ca10– P increased with soil depth increase. There is not obvious regular change of proportion of O– P. Ca-P was the most form in different forms of inorganic P, reached 82.65% of inorganic P, and the content of Fe– P, Al - P followed, the third is O– P. The content of Ca10-P took the most weight of Ca-P, and the second was Ca8-P.4. The correlation analysis showed that: total P activity significantly positive correlated with available P, total salt, nitrate and ammonium content. A significant correlation also existed between available P and total salt content. There is a significant correlation between inorganic P and ammonium content. Organic P activity slight correlated with total nitrogen, nitrate and alkali-hydro nitrogen content. Soil pH activity negative correlated with all different forms of phosphorus, just same as nitrate.5. The value of C/N, C/P, and N/P declined with the increase of cultivation years. Carbon has a low level in facilities vegetables cultivated soil. Phosphorus accumulated more than nitrogen.