Urea Phosphate Effects on Infiltration and Sodium Parameters of a Calcareous Sodic Soil
- John Ryan and
- Hadi Tabbara
There are potential advantages to using acidic fertilizers, especially in irrigation systems. Such materials improve water infiltration and permeability in soils whose structure is adversely affected by excess Na. A laboratory study evaluated urea phosphate (0–20 g kg−1 solutions), which contains H3PO4, with respect to initial infiltration of the urea phosphate (UP) solution and subsequently with water alone. A calcareous clay soil was equilibrated in columns with saline solutions [electrical conductivity (EC), 1.5 dS m−1] with sodium adsorption ratios (SAR) of 5, 10, 20, 40 and 60, to give varying exchangeable sodium percentages (ESP). Initial infiltration rates (IR) were enhanced only with the dilute UP solutions, i.e., 1.0 and 2.5 g kg−1, while all UP solutions improved subsequent infiltration with water alone. As the UP concentration of the infiltration solution increased, decreases occurred in soluble Na from the saturation extract and exchangeable Na, and estimated SAR. The improvement in IR was probably due to H3PO4 solubilizing CaCO3 for exchange reactions of Ca2+ with soil Na+. Urea phosphate may therefore enhance water use efficiency in some irrigated soils as well as serving as an effective source of N and P.
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