Phosphorus Status And Environmental Risk Of Phosphorus Leaching In Typical Vegetable Soils In The Suburb Of Hangzhou

Long-term and excessive fertilizer and manure phosphorus inputs to vegetable soils elevated P in soil solution and P leaching loss, which can lead to water eutrophication. There is critical need for a practical, simple and reliable method to assess the environmental risk of P loss potential from soils. The chemical tests, an incubation experiments and GIS were used to study soil phosphorus status, spatial distribution and the relationship between agronomic and environmental soil P tests in order to develop an indicator to assess the environmental risk of P loss potential in typical vegetable soils collected from suburb of Hangzhou.1. Chemical analysis was used to study soil phosphorus status and the relationships between agronomic and environmental soil P tests in order to develop an index to assess the environmental risk of P loss potential in typical vegetable soils collected from suburb of Hangzhou. The results showed that total soil P (TP) and soil-test P measured with CaCl₂-P. Olsen-P and P_M3 (Mehlich 3) with a wide range were 0.7～2.9 g/kg,0.48～19.64 mg/kg,10.65～151.60 mg/kg and 50.53-904.95 mg/kg, respectively. Of all the tested soils, 72% soils with Olsen-P exceeded agronomic optimum critical level of 60 mg/kg. DPS_OX ranged from 6.91 to 49.15% and DPS_M3 ranged from 5.82 to 52.56%. Positive significant relationships were observed between DPS and TP, Olsen-P and P_M3 Two methods of DPS calculations were linearly related to another. A split-line model related soil soluble P concentrations to the Olsen-P concentrations and DPS, indicating that the respective change points are: Olsen-P= 76.19 mg/kg, DPS_OX=26% and DPS_M3= 22%. Soluble P loss in leaching may be greater in soils with Olsen-P and DPS values that exceed these thresholds than in soils with lower Olsen-P and DPS values. More than 60% of the tested soils exceeded the above Olsen-P and DPS thresholds. It indicated that the environmental Olsen-P threshold is above agronomically optimum soil Olsen-P test value and, and therefore, if agricultural soils are below these environmental Olsen-P and DPS thresholds, then adequate crop P supply and environmental protection can both be achieved. 2. Chemical analysis and GIS technique were used to study nutritions, phosphorus status and spatial distribution of 150 vegetable soils collected from the suburb of Hangzhou. The results showed that 11% of all the tested soils with pH were below 5.5, the minimum was 4.6. That indicated the partial area was acidification. The soils with EC, OM, nitrogen and potassium values under agronomic optimum critical levels were 95%, 40%, 94% and 94% respectively. Soil nitrogen and potassium deficiency and phophorus accumulation were widely distribution in the tested soils. Of all the tested soils, More than 92% soils with Olsen-P exceeded agronomic optimum soil Olsen-P test value (60 mg/kg). The great variation in soil nutrient status and spatial distribution were observed at the tested area. The fields with high pH were at south and corner of northeast area, the fields with high EC were also at south area, the spatial distributions of OM, nitrogen and potassium were similar, the relative high level fields were at middle and partial south area, the spatial distributions of Olsen-P, TP, CaCl₂-P were also similar and the high P fields appeared at the east of whole area and part of southern area. A split-line model related soil soluble P concentrations to the Olsen-P concentrations and TP, indicating that the respective change points are: Olsen-P=78.58 mg/kg, TP=1.33 g/kg, 90% of all the tested soils were above Olsen-P or TP thresholds. Some controlling measures of P leaching loss to water and the optimum application managements were also recommended.3. An incubation experiment was carried out to study the effects of application rates of fertilizer on phosphorus status and leaching in the vegetable soils. The results showed IP-P and IP-N gave more contributions than other treatments to CaCl₂-P and Olsen-P released. Especially contribution of IP-N to CaCl₂-P was biggest in all treatments. The effects of incubation time and application rates of fertilizer on CaCl₂-P were very significant. The average accumulative rates of Olsen-P and P_M3 in the N-based treatments were above 25%, contrastingly these in the P-based treatments were only 20%. DPS was the efficient indicator for P leaching loss. Generally, DPS of the N-based treatments was higher than one of the P-based treatments and DPS of the N-based treatments exceeded DPS threshold value, the risk of P leaching loss was more significant than the P-based treatments. As the same P applicantion rates of the N-based, there were no significant variance in contributions to CaCl₂-P,Olsen-P,TP and P_M3 accumulated and DPS, that indicated effects of different P Sources on P accumulated and leaching were very similar in all N-based treatments.