Amounts, Forms, and Solubility of Phosphorus in Soils Receiving Manure
- Andrew N. Sharpley *a,
- Richard W. McDowellb and
- Peter J. A. Kleinmana
Continually land-applying manure at rates exceeding crop removal can change soil P chemistry and increase soil P to levels that are of environmental concern. To assess the effect of long-term manure application on soil P forms and solubilities, we determined water-extractable P, Mehlich-3 P, Hedley-P fractions, and crystalline Ca-P minerals in surface soil (0–5 cm) from 20 locations in New York (n = 6), Oklahoma (n = 8), and Pennsylvania (n = 6), which received dairy, poultry, or swine manure (40–200 kg ha−1 yr−1) for 10 to 25 yr. For all untreated and manured soils, the pH averaged 5.9 and 6.6; exchangeable Ca, 0.9 and 6.2 g kg−1; organic C, 15.7 and 32.6 g kg−1; and total P, 407 and 2480 mg kg−1, respectively. As Mehlich-3 P increased (64–2822 mg kg−1), the proportion that was water extractable (14–3%) declined as exchangeable soil Ca increased (R 2 = 0.81). Results suggest that addition of manure to soils shifts P from Al- and Fe- to Ca-P reaction products, accounting for the relatively greater Mehlich-3 but lower water extractability of soil P. This shift has implications to environmental soil P testing. For instance, the fact that Mehlich-3 P has been shown to overestimate potential losses of P in overland flow from heavily manured soils may be explained by dissolution of Ca-P minerals not soluble in water.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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