Evaluation of Full Factorial, Taguchi and Central Composite Design Methods in Reducing Nitrate Leaching from Soil under Zeolite Treatment

Use of nitrate fertilizer to increase crop yield is a method used by many farmers. Once this ion enters the soil, it is converted to nitrate and easily leached. Using zeolite is one of the methods to prevent nitrate leaching has received much attention today; however, determining the exact amount of nitrate fertilizer when using zeolite is very important. Performing experiments in a classic way and taking into account the effect of all factors (factorial design) needs time and cost in performing experiments. For this reason, old research methods should be replaced by simple and standard methods such as Taguchi and central composite design. For this purpose, this study was conducted in a completely randomized as factorial design. Treatments consisted of zeolite (at three amount; zero, 2 and 6%) and nitrate application (at three levels; zero, 200 and 400 mg nitrate per kg of soil) with three replications. Taguchi and central composite designs were considered with 9 and 13 experiments, respectively. The results of complete factorial method showed that the amount of zeolite had a significant effect on nitrate leaching; however, nitrate fertilizer had no effect on nitrate leaching. According to Taguchi results, both zeolite and nitrate fertilizer were very important on nitrate leaching reduction from soil. Based on prioritizing the effect in the central composite design, it was observed that zeolite was the most important factor in reducing nitrate leaching. Based on the results, the application of 2% zeolite was the beginning of the effect of zeolite on nitrate leaching. Therefore, it can be expected that in amounts between 2 to 6% zeolite, a significant reduction in nitrate leaching occurs.