Nutrients transport through variably structured soils

Abstract

Soil structure development has a direct and indirect relation with hydraulic properties that generally control the transport of surface applied nutrients in unsaturated zones causing environmental implications. Nitrate (NO 3-) and phosphate (H 2PO 4-) transport was assessed using undisturbed columns of variably structured calcareous soils, i.e. Shahdara (massive to weak coarse sub-angular blocky silt loam), Sultanpur (weak coarse, sub-angular blocky very fine sandy loam), Lyallpur (weak, coarse and medium sub-angular blocky silt loam), and Pacca (moderate, medium and fine sub-angular blocky silty clay). After conditioning the columns with 0.01M CaCl 2 (≈2 pore volumes), a pulse of KNO 3 (50mM) and KH 2PO 4 (32mM) solution was applied and afterwards leached with 0.01M CaCl 2. The experimental breakthrough curves (BTCs) of NO 3- and H 2PO 4- were described with one-domain and two-domain (mobile-immobile) convective dispersive equations (CDEs). Results showed that both NO 3- and H 2PO 4-, applied in the same pulse, appeared in the effluent almost immediately after pulse application and peaked after 0.4 pore volume cumulative drainage in Lyallpur and Pacca columns. In contrast, in the Sultanpur and Shahdara columns, appearance of NO 3- in the effluent was delayed till 0.6 pore volume and 0.4 pore volume cumulative drainage, respectively, and peaked at ≈1.0 pore volume cumulative drainage. The appearance of H 2PO 4- in the effluent was further delayed until 0.8 pore volume and 0.6 pore volume cumulative drainage, respectively. The despersivity, λ, that occurred in the Lyallpur and Pacca columns was significantly greater than in Shahdara and Sultanpur columns. While the fitted mobile water fraction, β, was significantly greater in Shahdara (0.81) and Sultanpur (0.90) than that of Lyallpur (0.27) and Pacca (0.28). It was concluded that variable structured soils had significant effect on solute transport parameters and should be considered in nutrient management studies. © 2011 Japanese Society of Soil Science and Plant Nutrition.