Impact of Irrigation Management Practices on Nitrate Leaching at Farmers Fields

Abstract

Irrigated agriculture in Pakistan like many other countries in the world has undergone transformations over the last few decades. Now it is supported by extensive irrigation system, mechanization and bio-chemical technology. Increasing trend of input factors in agriculture has raised fertilizer use manifold whereas, the associated practices of tillage and irrigation remain almost unchanged. Fear exist that the leached part of the fertilizer ultimately joins groundwater which is generally used for human drinking without any treatment particularly in rural areas, at least in this part of the world. Apparently injudicious management of fertilizer-tillage-irrigation matrix is resulting in wastage of fertilizer in addition to polluting groundwater reservoir. This necessities to intensify research for efficient use of irrigation water and other inputs such as fertilizer. This study was an attempt to investigate and create awareness amongst the researchers, planners, scientists and water users in polluting groundwater reservoir by fertilizer. A set of land, water and fertilizer management practices were studied under surge and continuous irrigations. Judicious use of irrigation water and fertilizer also have fringe benefits in terms of energy saving, controlling water table, reducing drainage effluent and increase in crop yields. This study was carried out in two phases: Phase-I: Developing and Calibration of Surge Automatic Value/Gate, and Phase-II: Field Investigation of Nitrate Leaching Behavior in Crop Rootzone. Nitrate Leaching under following level of treatments were studied • Method of water application (Surge Vs. Conventional Irrigation). • Dose of fertilization (Heavy Vs. Light). • Depth of irrigation water (Heavy Vs. Light). Results of the study revealed that the surge gate is best suited for low inflows. Surge irrigation helps in retaining the N03 within the rootzone. Furthermore, light irrigations and lower dozes of fertilizer play a pivital role in controlling the groundwater contamination. It was observed that after first irrigation, downward movement of nitrates was significantly affected by depth of irrigation, dose of fertilizer as well as sampling depth. The nitrate concentration was maximum in 0-30 and 90-120 cm soil depths for light and heavy irrigations respectively. This suggests that heavy irrigation causes excessive movement of nitrates out of crop rootzone particularly during early stage of crop growth when roots are shallow. Similarly, higher doses of fertilizer caused greater I movement of nitrates out of the crop rootzone compared with smaller dose of fertilizer. Further the various types of fertilizer behave differently on the mobiIity of nitrates. Two models were initially used in this study. Results of the LEACHN model were reasonably well. However, an overestimation trend was observed during calibration of the model with the observed data. ROSE model performed better in estimating the N01 leaching behavior within the rootzone for both surge vs. continuous irrigations under various doses of fertilizers. This model was employed in this study due to its simplicity and ease of operation.