Effects Of Agronomic Practices And Environmental Factors On Soil Phosphorus Transformation And Loss And Corresponding Mechanism

Intensive livestock and poultry production systems have generated large quantities of manures, which are readily available and abundant sources of nutrients for crop production worldwide. The land application of manure for the purpose of conditioning the soil and fertilizing crops is a common practice in the world. However, repeated land application of manures to meet crop nitrogen (N) needs can cause the buidup of large amounts of phosphorus (P) in the soil profile, leading to the risk of P loss to water bodies by runoff, erosion or leaching. Previous studies showed that P forms, quantities and migration of P are strongly influenced by manure application, however, effects of agronomic practices and environmental factors on P translocation, transformation and loss potential haven’t been clearly studied. Incubation experiments and in situ field experiments were performed on calcareous soils using chemical testing and microbial molecular ecology technique. This study aimed at evaluating the impact of manure application on phosphorus accumulation, translocation and transformation in a calcareous soil under different land use, studying the effects of rainfall and manure application on phosphorus leaching in field lysimeters during fallow season, deriving sorption indices for the prediction of potential phosphorus loss from calcareous soils, to study effects of phosphorus addition on phosphorus availability and microbial community structure, and to explore the effects of freeze-thaw cycles on phosphorus forms and translocation and microbial community structure. The main results were listed as follows:(1) Soil samples under different cropping systems (Vegetable, Cereal, and Tree) were collected to a depth of200-cm to evaluate the effect of manure application on soil P forms and quantities. It was shown that soil calcium bound P was the most abundant P fraction, followed by the residual P. Organic P only accounted for less than5%of total P in most of the soils. Manure application increased the levels of inorganic P (Pi), with higher proportions of Pi in labile forms than stable forms. After manure application for8-15yr, available P (Pois) and DPS values of the0-20cm layer in all sites exceeded the threshold for Olsen P (60mg kg-1) and DPS (30%) and the risk of P loss by runoff is expected to significantly increase. The DPS values were generally lower than30%below20cm, indicating a minimal risk of P loss via leaching Tom deeper soil. The results indicated that in typical peri-urban areas of the North China Plain,;he on-going practice of manure application not only caused P accumulation on topsoil, but also ncreased labile P, thus leading to high P loss potential, with the highest P loss risk found in vegetable soil.(2) A short-term field lysimeter experiment (53d) was performed to evaluate the effect of rainfall (low, high) and manure application (0,43kg P ha-1) on phosphorus (P) leaching from a calcareous soil in the fallow season. Our results showed that the P loading, irrespective of different extractions, was found below40cm in all treatments and P was most concentrated in the4-10cm soil layer. High rainfall enhanced P leaching and consequently led to lower water P (Pw) and higher leachate dissolved reactive P (DRP) and total P (TP) than low rainfall. Furthermore, P leaching was observed regardless of manure application, with the highest leachate DRP (1.83mg L"1) and TP (7.46mg L-1) concentrations found at the end of experiment (day53).Observed P leaching loads during fallow season (53d) varied between0.08and1.21kg ha-1. The thresholds of degree of P saturation (DPS) indicating P leaching were identified at18.9%DPSCaM3and12.9%DPS(Ca+Mg)M3, respectively. In this study, the DPSCaM3and DPS (Ca+Mg)M3values exceeded the corresponding thresholds in the upper30-cm soil layer but did not reach the thresholds at30-40cm. Nevertheless, the leachate DRP and TP indicated soil P leaching. The results showed that intensive rainfall could significantly increase P leaching from manure application. Moreover, P leaching could occur in fallow season even in the absence of manure input, which should be assessed by not only soil P sorption capacities, but also soil fertilization history and hydrologic conditions. Implementation of soil P level evaluation is critical before spreading manure on land to avoid P pollution. Cost effective and applicable soil test methods are required to generate environmental indicators to classify agricultural lands for risk of P loss, providing basis to safe manure disposal.(3) Seventy five soils mostly from Northern China were analyzed for developing techniques to evaluate soil phosphorus (P) sorption capacity (PSC) and determine critical soil P levels to predict P loss potential for calcareous soils. Strong correlation was found between PSC150and St (r2=0.89, p<0.001). The sum of αCaM3and βMgM3as an index of PSC (PSC(CaM3+MgM3)) was most closely related to the maximum amount of P sorbed (Smax) as given by the sum of St and soil initial P setting α=0.039and β=0.462(r2=0.80, p<0.001). The degree of P saturation (DPS) was thereafter calculated from PSC(CaM3+MgM3)(DPS(CaM3+MgM3)), to which Olsen P (Pols) was significantly correlated (r2=0.82, p<0.001). In a split-line regression from Pw against DPS(CaM3+MgM3)(r2=0.87, p<0.05), a change point was identified at28.1%DPS(CaM3+MgM3), which was equivalent to49.2mg kg-1Pols and corresponded to a Pw concentration of8.8mg kg-1. After the change point, a sharp increase in Pw was observed. Our results reveal a new approach to approximating DPS from CaM3and MgM3for calcareous soils without the need to generate a Smax. We conclude that in the absence of an environmental soil test criteria for P, the DPS(CaM3+MgM3) and Pois could be used to predict P loss potential from calcareous soils. (4) An incubation experiment was performed to study the effects of different phosphorus additions (swine manure, compost and fertilizer). Results showed that the three P additions can increase Olsen P (Pols) content and enhance P release, with the significant effect found under fertilizer addition. As time prolonged, Pols concentration decreased with fertilizer addition, while there was no change with manure and compost additions. Phospholipid fatty acid analysis (PLFA) revealed that manure greatly increased fungal, bacterial and total PLFA biomass, fungal/bacterial ratio, and phosphatase activities, while actinomycetes were not affected. Besides, compost greatly increased total PLFA biomass and alkaline phosphomonoesterase activity, whereas, biomass of fungal, bacterial and actinomycetes, acid phosphomonoesterase or phosphosdiesterase activities were not influenced. For fertilizer addition, fungal, bacterial and total PLFA biomass didn’t change, while phosphatase activities were decreased. Therefore, P availability could be increased by different P additions, with the most significant increase observed with fertilizer. Moreover, fertilizer could decrease phosphatase activities and have no effect on microbial community structure, however, manure and compost can favor organic P hydrolysis by increasing phosphatase activities and PLFA biomass, thus providing sustainable P supply.(5) An incubation experiment was carried out to study the effects of long-term freeze thaw cycles (FTCs)(53cycles,424d) on phosphorus (P) transformation, release characteristics and corresponding mechanism. Our results showed that microbial biomass carbon (C) and P as well as bacterial biomass were significantly reduced by FTCs, while phosphosdiesterase activity was increased and the responses of fungal and actinomycetes biomass as well as phosphomonoesterase activities to FTCs were affected by soil P levels. Furthermore, labile P concentration and the proportion in total P (TP) were significantly increased by FTCs, while the organic P (Po) content and the proportion in TP were obviously decreased. Soil P release characteristics showed that P release was reduced by FTCs, especially in high P soils. Therefore, FTCs could enhance Po hydrolysis by releasing soil biomass P, shifting microbial community structure and increasing phosphatase activities, thus improving soil P availability.