Micronutrients Losses from Soil under Subsurface Drainage System

Abstract

The drainage system, although it reclaims waterlogged soils, poses a potential threat to leaching of valuable nutrients. To assess the micronutrient losses from such system established more than two decades ago in the plains of northwestern Pakistan, drainage waters were periodically analyzed for selected micronutrients. The inputs of micronutrients in irrigation waters were also determined. The micronutrient removal in drainage water was 1.39 to 9.79 times greater than micronutrient inputs in irrigation waters and fertilizers. Among micronutrients, the removal of copper (Cu) and manganese (Mn) in drainage water was greater than iron (Fe) and zinc (Zn). The concentrations of micronutrients generally changed with cropping (sampling time), increased with soil depth, and were invariably negative on the nutrient balance sheet, suggesting that these nutrients are continuously depleted from the system in drainage water. These nutrients therefore must be replenished in soil through an appropriate means for optimum crop yields under the given drainage–irrigation–cropping system.