Study On The Dynamic Changes And Influencing Factors Of Phosphorus Enrichment In Facility Agricultural Soil

With the adjustment of agricultural structure and the improvement of people's living standards, there is a large demand for high quality anti-season facility agriculture. Therefore, the development of facility agriculture is extremely rapid, which plays an important role in improving the efficiency of agriculture, income of farmers and the economy of countryside. Phosphorus is one of the requisite nutrient elements for plant growth. Not only it is an important component of organic compounds, but also participates in various metabolic processes inside plants in different ways. The phosphorus which is absorbed by plants is mainly come from the soil. The fertility of greenhouse soil is closely related to the production and quality of crops and economic benefits. The degradation of soil quality has become a main factor which influences the quality, benefit and sustainable development of facility agriculture. During production, facility agriculture is always in semi-closed condition, and has the characteristic of high temperature, humidity and fertilizer inputs, shorter and more vegetable growth cycles and more output, etc. Farmers lack the know-how of systematically understanding of the special facilities environment, so blindly application of phosphate is very common, which causes the application of phosphate far exceed the demand of vegetables. Phosphorus nutrients in the soil of facilities agriculture enrich extensively, which causes problems such as unbalanced nutrient, low fertilizer efficiency, salt enrichment, soil acidification, soil environment pollution, low vegetable quality and waste of resources. Consequently, all of the above problems seriously affected the yield, quality and benefit of crops. In order to find the dynamic change law of phosphorus enrichment in facility agricultural soil, and the relationship between phosphorus nutrients and soil pH, organic matter, soil texture, nitrogen nutrient, rapidly-available potassium, cadmium and enzymes in the soil. Through the investigation of facility agriculture, experimental analysis and systematic comparison of facilities agriculture soil after different years of planting and different layers at Zichang (Yanan), Yang ling and Baoji, the conclusion is as follows:(1) The total phosphorus, rapidly-available phosphorus, inorganic phosphorus and organic content in facilities agricultural soil are higher than the control field, and there is a significant difference between soil of different planting years and in different layers. Under the circumstance of the facilities agriculture, long-term massive application of phosphate fertilizer make tilth soil phosphate, not only in 0 20cm, but also in 20 40cm, enrich extensively. With the increment of planting years of facility agriculture, all kinds of phosphate increased year by year at different speed, but the content of phosphate decreased gradually with the depth of the soil.(2)With the increment of planting years, the content of organic and inorganic phosphorus in facility agriculture increased significantly. The increment of the phosphorus is mainly inorganic phosphorus, which occupies 69.88% of the soil phosphorus, and organic phosphorus accounts for 30.12% of the total soil phosphorus. In inorganic phosphorus components, Ca₂-P, Ca₈-P, Al-P, Fe-P, O-P and Ca₁₀-P enriched at different levels, and the content of them decreased with the soil depth with the increment of planting years. Inorganic phosphorus enriched in different layers of soil is mainly Ca-P (including Ca₈-P, Ca₁₀-P and Ca₂-P), which occupies 72.91% of the inorganic phosphorus, and the next is O-P,Al-P and Fe-P, which accounts for 14.20%, 7.38% and 5.50% of the inorganic phosphorus, respectively. In all types of Ca-P, the highest content is Ca₁₀-P, which is 388.25mgï¹’kg^-1,accounts for 54.67% of Ca-P, and the next is Ca₈-P and Ca₂-P, which occupies 32.37% and 12.96% of Ca-P. In 0⁴0cm soil profiles, the increasing extent of Ca₈-P, Ca₂-P and Al-P is relatively wide with the increment of planting years, and increasing extent of Ca₁₀-P, O-P and Fe-P is relatively less.(3)Changing trend of the organic phosphorus content is in accordance with other forms of phosphorus. In the soil profile, the content of organic phosphorus in the 0-20cm is higher than 20-40cm, and the content increase gradually with the increase of soil depth and planting year.(4)The soil pH, organic matter, total nitrogen, alkali-hydrolysable nitrogen, nitrate nitrogen, ammonium nitrogen, and available potassium and cadmium changes obviously, pH decreases with the cultivation year of facility agriculture, but increased with the depth of soil layers. Organic matter, total nitrogen, alkali-hydrolysable nitrogen, nitrate nitrogen, ammonium nitrogen, available potassium and cadmium content were higher than those of control field, and enriched greatly with the increment of planting years, but decreased with the increment of soil depth. The soil texture is in the range of 0-40cm, <0.05mm,<0.02mm,<0.01mm,<0.005mm and <0.002mm soil particle content decreased with the increment of planting years, but increased with the increment of soil depth. The activity of catalase, urinary enzyme, invertase and phosphatase increased with the increment of planting years (there is a significant difference between different planting years and soil layers), but decreased with the increment of soil depth.(5)There is an extremely significant negative correlation between the soil pH and phosphorus of facility agriculture (total phosphorus, available phosphorous and organophosphorus), and an extremely significant positive correlation between the organic matter and phosphorus nutrients. The content of total nitrogen, alkali-hydrolyzable nitrogen has an extremely significant positive correlation with phosphorus nutrients. After 28 days cultivation, there is a significant negative correlation between the content of nitrate nitrogen (NO^3--N) and phosphorus nutrients, and there is a positive correlation between the content of ammonium nitrogen (NH⁴⁺-N) and phosphorus nutrients. The content of available potassium has an extremely significant positive correlation with phosphorus nutrients. There is a extremely significant negative correlation between the content of <0.05mm, <0.02mm, <0.01mm and <0.005mm soil particle and phosphorus nutrients, and <0.002mm soil particle has a negative correlation with phosphorus nutrients. There is an extremely positive correlation between the urinary enzyme, invertase, phosphatase and phosphorus nutrients, and the enzyme activity enhanced gradually with the enrichment of phosphorus. There is an extremely positive correlation between the content of cadmium and phosphorus nutrients, and the content of cadmium increased gradually with the enrichment of phosphorus nutrients.