ارزيابي تلفات نيترات در كود آبياري جويچه اي با استفاده از داده هاي مزرعه اي و يك مدل رياضي كودآبياري

Evaluation of Nitrate Losses in Furrow Fertigation by Field Data and Model Analysis

In this study, a corn-field furrow irrigation was conducted to investigate the effect of fertigation on distribution uniformity and nitrate losses through surface runoff. Twelve experiments were carried out during two years (2008 and 2009) in free drainage furrows having 165 m length and 0.006 m/m slope in Karaj. Required fertilizer was applied based on soil analysis in four stages during the growing period: before planting, in seven- leaf stage, shooting stage and earring stage. The outflow from the experimental furrows was measured by WSC flumes. Nitrate concentration of water samples taken during the experiments was analyzed by spectra photometer. Collected data during the first year were used to specify the best time of fertilizer injection in order to achieve the lowest fertilizer losses. The results revealed that the best time of injection was 20 minutes in the end of irrigation. This time was used to apply the fertilizer in second year. Runoff- losses of nitrate in the first year ranged between 5.7 to 42 percent whereas in second year using optimized time (20 min) nitrate losses through runoff was 1.4 to 12.3 percent. Also, the results of the fertigation model showed that the model estimated water and fertilizer losses reasonably well. The correlation coefficient between measured and predicted data by the model was 0.85 and 0.8 for water and fertilizer losses, respectively during two years of experiment. Key words: Fertigation, Nitrate losses, Fertigation model, Furrow irrigation