Effect of Soil Temperature and Length of Reaction Period on Water Solubility of Phosphorus in Soil Fertilizer Reaction Zones1
- J. D. Beaton,
- R. C. Speer and
- G. Brown2
Pellets containing 15 mg of P prepared from each of the following salts: KH2PO4 (MKP), NH4H2PO4 (MAP), (NH4)2HPO4 (DAP), Ca(H2PO4)2·H2O (MCP), and CaHPO4·2H2O (DCPD) were placed in cavities in the surface of Bradwell very fine sandy loam (pH = 7.8) and Monroe silt loam (pH = 5.8). The treated soils were stored at 5, 20, and 35C. Extent of dissolution of fertilizer pellets and development of soil-fertilizer reaction zones were measured during the first 14 days of storage. At the end of 2, 7, 14, 28, and 56 days the soil-fertilizer reaction zones were sampled and the concentration of water-soluble P and the percentage of fertilizer P soluble in the reaction zones were determined.
Rate of dissolution of the water-soluble P fertilizers increased markedly as temperature increased. Some pellets were incompletely dissolved at the end of 14 days at 5C, whereas, at 35C dissolution was usually complete in less than 4 days. For each 15C increase in temperature there was about a 33% reduction in concentration of water-soluble P and the proportion of fertilizer P soluble in water.
During the first 14 days after adding the water soluble fertilizers there was a rapid decrease in concentration of water-soluble P and proportion of dissolved fertilizer P while after 14 to 28 days the changes were much samller. Extraction of water-soluble P decreased in the order MKP>MAP = DAP>MCP>DCPD>check. Differences among sources became smaller with increased time of contact with soil. DCPD was more soluble in the acid Monroe soil than in the calcareous Bradwell soil.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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