Modeling solute transport in soil under conventional plow-based and conservation agriculture production systems in Claveria, Misamis Oriental, Philippines

In the Philippines, no research has yet been done that compares the solute transport behavior of soils under conventional plow-based and conservation agriculture production systems. Hence, this study aims to model and to compare the solute-transport behavior of soil under the aforementioned production systems. Undisturbed soil core samples were taken from both production systems from experimental sites in Claveria, Misamis Oriental. Miscible displacement and adsorption experiments were performed at the laboratory. A stochastic method, following continuous-input soil column tests, determined the dispersivity of the soil samples while a laboratory flow-through method, using pulse-input soil column tests, calculated the retardation factor. Both the soil dispersivity and the retardation factor were optimized using the CXTFIT/Excel to fit the observed values to the Convection-Dispersion Equation. Upper-layer plow-based soil, with a combined lowest retardation factor 1.26 and dispersivity of 17.5 cm, had the highest peak concentration of 0.07 C subzero and the shortest time-to-peak of 44 s. Conservation agriculture soil, having a high retardation factor of 6.54 in spite of the highest value of dispersivity of 27.3, exhibited the lowest peak concentration of 0.44 C subzero after nearly 7 min of peaking time. These results may be indicative of macroporosity in plow-based soils, as well as higher organic carbon content in conservation-agriculture soils. Model efficiencies ranging from 77% to 98% signify that the Connection-Dispersion Equation is able to adequately predict solute transport in these soils. Simulations of solute transport in response to changing soil organic carbon content for a ten-year period were performed. Increasing the organic carbon by 30% in conservation-agriculture soils reflects a 9.6% decrease in peak concentration and a 3.1% increase in time-to-peak. Whereas, there are minimal changes in terms of both peak concentration and time-to-peak when plow-based soils assumed 3% decrease in organic carbon. The combination of low dispersivity and high retardation factor may prove to be beneficial in terms of fertilizer and pesticide application, nutrient uptake by crops and minimized leaching into the ground water. Conservation agriculture production systems may achieve the two said conditions and set economic and environmental precedents.