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Excess phosphorus (P) from agricultural soils contributes to eutrophication in water bodies.Samples (n=60) were taken from sites where rice paddies have been converted to vegetable fields for 0,< 10,10-20,and > 20 years and analyzed for five inorganic P (Pi) fractions,three organic P(Po) fractions,and several soil parameters to investigate how land use conversion affects Pi and Po fractions in a peri-urban area of China with soils characteristic of many agricultural areas of Asia.Significant increases of 33,281,293,and 438 mg kg 1 were found for soluble and loosely bound Pi (SL-Pi),aluminum-bound Pi (Al-Pi),calcium-bound P i (Ca-Pi),and iron-bound Pi (Fe-Pi),respectively,after conversion from rice paddies to vegetable fields.Most of the increase in Pi was in the form of Fe-Pi,which increased from 8% of total P (TP) on paddy soil to 31% on the soil with > 20-year vegetable cultivation,followed by Al-Pi,which increased from 2% to 19% of TP.For Po fractions,there was no significant change in P concentrations.The conversion of land use from paddy fields to high intensity vegetable fields was causing significant changes in soil P fractions.Management practices were causing a buildup of soil P,primarily in the Fe-Pi fraction,followed by Ca-Pi and Al-Pi fractions.If current trends continue,a 30%-70% increase in TP could be expected in the next 20 years.Farmers in the area should reduce P application and use to maximize P uptake.
Excess phosphorus (P) from agricultural soils contributes to eutrophication in water bodies. Samples (n = 60) were taken from sites where rice paddies have been converted to vegetable fields for 0, <10, 10-20, and> 20 years and analyzed for five inorganic P (Pi) fractions, three organic P (Po) fractions, and several soil parameters to investigate how land use conversion affects Pi and Po fractions in a peri-urban area of China with soils characteristic of many agricultural areas of Asia. Significant increases of 33,281,293, and 438 mg kg 1 were found for soluble and loosely bound Pi (SL-Pi), aluminum-bound Pi (Al-Pi), calcium- bound Pi (Ca-Pi), and iron-bound Pi (Fe-Pi), respectively, after conversion from rice paddies to vegetable fields. Host of the increase in Pi was in the form of Fe-Pi, which increased from 8% of total P (TP) on paddy soil to 31% on the soil with> 20-year vegetable cultivation, followed by Al-Pi, which increased from 2% to 19% of TP.For Po fractions, there was no significant change in P concentrations. The conversion of land use from paddy fields to high intensity vegetable fields was causing significant changes in soil P fractions. Management practices were caused a buildup of soil P, primarily in the Fe-Pi fractions, followed by Ca-Pi and Al-Pi fractions. Current trend continue, a 30% -70% increase in TP could be expected in the next 20 years. Farmers in the area should reduce P application and use to maximize P uptake.