Effect of hog manure on soil phosphorus forms
Application of livestock manure can benefit crop production as a valuable source of nitrogen (Bandel and Fox 1984; Campbell et al. 1986; Chase et al. 1991). However, phosphorus is not a negligible factor as phosphorus in livestock manure may be readily used by crops (Tunney, 1981; Stewart, 1992). Generally, the rate of manure applied to the field to meet the crop nitrogen requirement in the year of application is often the first consideration. Under semi-arid conditions in the prairies, rates in excess of the crop's nutrient demand in the year of application may result in nutrients in manure in both organic and inorganic forms left over after harvest, which may pose environmental concern if nutrients escape the soil system before they are used by subsequent crops (Schoenau et al., 1999). In a scenario of repeated high rates of manure added every year, excess P is a concern as N:P ratio in manure may be lower than N:P ratio required by crop uptake. However, in the first year of application, the manure addition may not significantly increase extractable P in soils. The fate of manure P in the soil P cycle deserves attention in Saskatchewan soils. Manure addition changes different pools of soil P, especially at higher P rates as fertilizer or manure (Campbell et al., 1986; O'Halloran, 1993). However, most of the previous studies have only reported long-term effects of several years of manure addition (Dormaar and Sommerfeldt, 1986; N'dayegamiye and Angers, 1990; McKenzie et al., 1992a; Dormaar and Chang, 1995). Information on short-term effect is needed to help understand P availability and potential P mobility in soils receiving manure for the first time, an important consideration as the swine industry expands in Western Canada. Thus, we designed an incubation experiment and used a sequential extraction technique to identify changes in P forms and assess manure P dynamics two and sixteen weeks after addition of liquid swine effluents. Urea was added at the same rate of manure N for comparative purposes.
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