Accumulation and Leaching Risk of Phosphorus in Vegetable Soils under Intensive Cultivation
|School||Nanjing Agricultural College|
|Keywords||vegetable soils phosphorus accumulation adsorption-desorption fertilizer utilization efficiency soil enzyme leaching|
Field sampling survey, soil sample analysis, pot cexperiment and laboratory soil column leaching simulated experiments were carried out to study the characterists of phosphorus accumulation, the adsorption-desorption and fraction and distribution of P. Additionally, the effects of different phosphorus fertilizers applied on high-phosphorus, phosphorus soil leaching and the assessment of phosphorus leaching risk in Nanjing suburb vegetable soils were also studied. Thereby formulating indicators to assess the environmental risk of phosphorus loss potential in typical vegetable soils collected from suburb of Nanjing. The obtained results were listed as follows:In order to study soil phosphorus accumulational characteristics and the risk of phosphorus leaching, we assayed the concentrations of total phosphorus (TP), available phosphorus (Olsen-P), dissolved reactive phosphorus (CaCl2-P) and bio-available phosphorus (NaOH-P) in soil samplies which have been cultivated continuously for 3 to 5, 15 to 20 and 25 to 30 years respectively. The phosphorus adsorption-desorption characteristic was also studied by analysing the layer of 0-20 cm sampled soil. The risks of phosphorus loss in soil were evaluated through studying the degree of phosphorus saturation (DPS) and the value of maximum buffer capacity (MBC). The results indicated that the longer period of vegetable cultivation was, the greater accumulational degree of phosphorus would be excepted for NaOH-P. The TP, Olsen-P, CaCl2-P and NaOH-P were mainly accumulated in the 0-20 cm soil layer where as the accumulated phosphorus decreased in proportion to the depth of sampled soil. The phosphorus isothermal adsorption curve and adsorption-desorption curve could be well presented by Langmuir equation and quadratic equation. With the increase of cultivation years, the maximum phosphorus adsorption quantity and MBC of the surface soil decreased significantly in the sampled soil, while DPS and phosphorus desorption rate increased. Moreover, the longer cultivation years, the greater phosphorus desorption rate. Phosphorus desorption rates of the vegetable soils cultivated for 15 to 20 and 25 to 30 years were significantly higher than that of has being cultivated for 3 to 5 years. The correlational analysis of main factors affecting the soil phosphorous adsorption-desorption, such as MBC and DPS, revealed that the amorphous Fe-Al content of soil significantly affected the characteristic soil. With the increase of cultivation years, adsorption-desorption.A pot experiment was conducted with five rate (0,75,150,225 and 300 mg·kg-1) of phosphorus fertilizer to determine agronomic characters, soil properties and P fertilizer utilization efficiency of cabbage in response to fertilizer phosphorus ratio on high phosphorus testing soil with 232.59 mg·kg-1 at the net room of Jiangsu Academy of Agricultural Science in Nanjing. The results showed no significant yield increase with the increase of phosphate fertilizer by using such methods. Absorbed nitrogen and potassium were mainly accumulated in the leaves and stems of those different varieties of cabbage under such experimentations, whereas phosphorus was mainly stored in the roots. With the increase of phosphate fertilizer there was an increasing trend of total nitrogen, total phosphorus, total potassium accumulation in plants and reducing the phosphorus utilization efficiency. Compared with no phosphorus fertilizer application, all P fertilizer application treatments had no significant difference on acid phosphatase activity. With increasing phosphorus application rate, there was a reducing trend of urease and sucrase activity in "Shanghai Qing", but no marked effect in "Si Ji" and "Huang Yang". In the phosphate fertilizer was 225 mg·kg-1 sucrase activity increased significantly in "Ai Jiao Huang"Leaching characteristics of high phosphorus vegetable soils with high salinity, high acidified soil and conventional vegetable soils were studied. The results showed:with the increase in the amount of leaching, three kinds of vegetables, high phosphorus content of soil EC, NO3-, K+ and Na+ concentration in the elution volume of 150 mL (8 d), the leaching quantity reached its maximum, continue leaching, leachate EC, NO3-, K+ and Na+ concentration were rapidly reduced, but the TP concentration in leaching solution reached its maximum at the 28th day (350 mL). The leachate soluble P content remained at a high level in three kinds of high phosphorus contentional soil after 57 days leaching. Then the TP and PO43- leaching had hysteresis and continuity, so phosphorus had more potential environmental hazards.