Phosphorus Loss From Paddy Soil In Northern Zhejiang

Phosphorus (P) is one of essential elements for rice production, particularly in the area short of ready P in paddy soil in China. Due to rapid transformation of P in soil and low efficiency of P uptake for crop, P input could be easily built-up in agricultural land. Inland water eutrophicaiion is normally accelerated by P transferred mostly from agricultural soil into nearby waters currently through various pathways.A field experimental trial for this study was set up in Shuangqiao farm, Northern Jiaxing city, Zhejiang province, which was closely located near the common boundary connected with Shanghai metropolis, Zhejiang province and Jiangsu province. The field plot experiment coupled with operation of simulated artificial rainfall was conducted for the purposes listed as: P uptake efficiency and potential risk of P loss under different rates of P application, seasonal P export loads through surface runoff and leaching individually, best P application beneficial for both agronomy and environment.1. Paddy plots experiment.a.The accumulative P loss load by rainfall-induced-runoff ranged from 0.179 to 0.454kg P/ha, between 1.72 and 1.82% of seasonal fertilizer-P application.b.Remarkable linear relationship between runoff P export load and intensity of rainfall was found with the regressive equation as Y= 0.05164xX₁+0.04182xX₂-6.197 (R2=0.8136, n=9), where Y, X₁ and X₂ were defined as runoff P loss load (kg/ha), intensity of rainfall (mm), application rate of P fertilizer (kg/ha).c.The variation of total phosphorus (TP) over time in subsurface flow was similar to that of vertical leaching. Field drying process could apparently enhance TP concentration in subsurface flow.d.The seasonal P loss through vertical leaching under the treatment of P0, P1, P2 were found as 0.036, 0.101, 0.186kg P/ha, respectively, while 0.016, 0.023, 0.031kg P/ha were recorded respectively in term of P loss through subsurface flow.e.Surface runoff was found the main pathway for P export from soil. 77.5%, 72.2%, and 67.7% of total loss load of P were found at the three treatments of P0, P1, and P2, respectively. However, droughty weather status in 2003 would enhance P leaching loss ratio, which is worth of further validation.f.The optimal fertilizer level for increasing production was observed under the treatment of N3P1, with the increment of rice yield between 4.1% and 9.1%. According to the local routine P application, total P input to paddy soil was recorded as 21.80kg P/ha while the total output reached as 39.72kg/ha, with the net P balance of -19.72kg/ha. Because abundant P fertilizer had been input for the continuous past 20 years which resulted in a comparative high concentration of Olsen—P in the top soil, subsequently the current soil P level in the local paddy field is believed to maintain the regular rice yield.2. Simulated artificial rainfall experiment.a.Surface runoff occurred approximately 2.0, and 5.8 minutes after simulated rainfall operated under the intensity of rainstorm, and heavy rain, respectively.