Effects Of Manure Application On The Form And Mobility Of Soil Phosphorus In Vegetable Greenhouse

Heavy manure application with excessive and frequent irrigation in vegetable greenhouse caused high accumulation of phosphorus (P) in soil and high risks of P loss. In this study, the data from literatures, surveys on greenhouse fields and livestock farms, and long-term experiments were used to (1) evaluate the contribution of manure application on P accumulation in soil under greenhouse vegetable production;(2) investigate the effect of manure application on the form and mobility of soil P;(3) analyze the influences of addition of high chemical nitrogen (N) fertilizer and straw on the form and mobility of soil P. Hedley sequential P extraction method was used to analyze P forms in manure and soil. Major results were summarized as follows:(1) Phosphorus surplus was527kg P hm-2per season in vegetable greenhouse. Excess P input led to soil enrichment of labile P, measured as Olsen-P, averaging179mg P kg-1in the0-20cm soil depth and the values were higher than that in open vegetable field and cereals field. Soil Olsen-P of nearly87%greenhouse sites exceeded the environmental threshold (80mg P kg-1). P leaching obviously occurred in vegetable greenhouse, as evidenced by increases in Olsen-P and CaCl2-P in the20-100cm soil depth and P leaching was enhanced with the increase of planting years.(2) Manure P accounted for54.3%of total P inputs in vegetable greenhouse. The annual increase in soil Olsen-P in the surface layer (0-30cm) was0.034mg kg-1per1kg ha-1surplus P in vegetable greenhouse with flood irrigation. Application of manure significantly increased the increasing rates of soil available P and degree of P saturation (DPS).(3) Significant differences were observed in total P content of different kinds of animal manure and mean P contents ranged from7.5to22.5g P kg-1. High proportion of inorganic P in total P (60-70%, except for duck manure with34%), low C/P ratio (<50) and high liable P fraction (H2O-P, P extracted by deionized water+NaHCO3-P, P extracted by NaHCO3solution>40%) led to high availability of P in animal manures. The content of total P in non-ruminant animal manure (pig, chicken and duck manures) was1.7-3.0folds greater than that in ruminant manure (cattle and sheep manures) and C/P ratio in the former was lower than that in the latter. The proportion of HC1-P (P extracted by HC1solution) in total P in non-ruminant animal manure (34.4%) was greater than that in ruminant manure (15.2%), but the proportion of NaHCO3-P in total P in the former (19.4%) was lower than that in the latter (32.8%). There were no significant differences in other P fractions between the two types of manure.(4) Application of manure significantly increased labile P fraction and DPS, which in turn increased the mobility of P in soil, especially inorganic P (Pi). Results of Shouguang experiment showed that Pi accounted for90%of annual P leaching loss below90cm soil depth. And the increasing proportion of H2O-P mainly contributed to the downward transport of P in manure application treatment. Results of Daxing experiment showed that manure application decreased the proportion of HCl-Pi in total P and promoted the leaching of Ca, and it indicated that the dissolution of Ca-P due to pH decrease influenced by manure application may be the strategy of Pi leaching in vegetable greenhouse with high soil pH. Manure application increased the contents of H2O-Po (Po, organic P) and its proportion in total Po. Results of Shouguang experiment showed that H2O-Po was30-40mg P kg-1in0-60cm depth soil. Therefore, the contribution of Po to transformation and transfer cannot be neglected.(5) Addition of straw significantly decreased contents of HCl-Pi in0-30cm depth soil, and increased contents of NaHCO3-Po and NaOH-Po (Po extracted by NaOH solution) in30-60cm depth soil. Addition of straw also significantly increased H2O-Pi content and its proportion in total P in60-90cm depth soil, and annual Pi leaching loss below90cm soil depth. It is indicated that addition of straw favor Po leaching, but mineralization of Po may occur during the P movement to deeper soil.(6) Heavy application of N fertilizer (urea) significantly decreased pH and promoted the transformation of HCl-Pi to NaOH-Pi in0-60cm depth soil. It also markedly increased the content of Po in60-90cm depth soil, P leaching loss and the proportion of Po in total P leaching losses below90cm soil profile, respectively. Additionally, N fertilization significantly increased the content of NaHC03-Po in30-90cm depth soil. And the proportion of NaHCO3-Po in total soil P increased with the soil depth increasing. It is indicated that NaHCO3-Po is an important form of Po movement under high N input system. In vegetable greenhouse with calcareous and high P content soil, soil acidification influenced by urea-N fertilizer application and an enhancement of Ca-P and CaCO3dissolution is the main strategy of inorganic P mobility increasement. In addition, Po mobility increasement is largely due to the increase of Po fraction.