Soil Nutrient Distribution Of Farmland And Phosphorus Loss In The Plain River-network Area Of Jiangsu Province

From March2009to June2010, taking the farmland in the town of Changdang in Sheyang County,Yancheng city as the representative research area, through the field observation and laboratory analysis, soil nutrient distribution and phosphorus loss potential under different land use patterns, phosphorus loss from farmland runoff-plots, and polder scales were investigated. The main research results are as follows:(1)The different land use patterns affect the value of pH, content of organic matter of soil. The value of pH is highest in the soil which has been grown rice-rape/wheat for1year. The content of organic matter is highest in the soil which has been grown soybean for1year, but the differences are not significant. The difference of TN contents under different land use patterns is not significant. For the contents of alkali-hydro nitrogen, TP(Total Phosphorus, TP), organic matter, Olsen-P, CaCl2-P(CaCl2-Extractable Phosphorus, CaCl2-P), WSP(Water-and/or Dilute Salt-Extractable Phosphorus, WSP), Phosphorus adsorption and PSI(Phosphorus Sorption Index, PSI), the difference is significant. Organic matter shows significant positive correlation with each item except for PSI. TP, Rapidly-available potassium, Olsen-P, CaCl2-P, WSP show significant positive correlation with them each other, and show significant negative correlation with PSI.(2) Vegetable land soil received a lowest PSI content and highest WSP content,60.6/kg and5.834mg/L respectively, which mean got a highest risk of phosphorus loss. The sustained growing of cotton-wheat/barley improved soil phosphorus ability and effectiveness of various nutrients, but increases the risk of phosphorus loss. PSI value of cotton-wheat/barley is only higher than vegetable land and fallow land.(3) Taking the heavy rainfall event in July,2009for example, in the initial period of the event, the phosphorus losses in the main form of particle phosphorus, the proportion is79%, and with the rainfall continuing, content of particle phosphorus reduces to the30%of TP. The main form of DTP(Dissolved Total P, DTP) loss is DIP(Dissolved inorganic P, DIP).(4) As the rainfall precipitation increased, the particle phosphorus loss from the polder scale intensified gradually during the rape seedling stage. And, the dominant species form of the polder scale farmland was particle phosphorus at the bud stage. Before the flowering stage arrival, the underground soil phosphorus loss occurred, of which94%was DOP.(5)The runoff of the polder scale farmland occurred mainly from July to September. The drainage runoff TP concentration curves showed a wave shape. The highest concentration of TP was0.235mg/L; and the lowest was0.120mg/L. The DP(Dissolved P, DP) flowed away mainly by the form of DIP. The variation of the runoff DIP was relatively consistent with the change of the DP. During storm events, the small drainage runoff peaks lagged behind the runoff peaks. With the shrinking of the runoff coming, the dominant form of the phosphorus loss was the particle phosphorus; while the runoff let down, the most of the phosphorus was DIP.(6)The values of SMC (site mean concentration, SMC) of phosphorus loss in several rainfall runoff events were different. The highest SMC amounted to0.344mg/L in June,2009; and the lowest was0.094mg/L which happened in September,2009. Moreover, the total runoff phosphorus amount of the cotton lands in July and August was about74.5%of the annual total phosphorus loss. Also, the phosphorus transport flux via surface runoff in cotton land was41.5mg·m·a-1.