Optimal Nitrogen Fertilization for Potato and its Potential Effects on Ground Water

This study was conducted in Tubas district, which is considered an important agricultural district especially in irrigated agriculture. The experiment was conducted at an agricultural field located within Wadi Fara’ (Ras El-Fara’) which is an important irrigated agricultural area rich with ground water (Fara basin’) Water is available for irrigation purposes and for domestic use in Tubas and Nablus through a number of natural springs and wells. Potatoes crop was selected for the study, as it is one of the most important irrigated agricultural crops in the area. As a result of excessive use of nitrogen fertilizers for this crop as well as other crops, there is a danger of increasing nitrates concentrations in the wells and springs in the area. To reduce such possible problems, this study was conducted to determine the optimal nitrogen fertilization needed for potatoes. This optimal amount will be recommended to farmers through agricultural extension services. As a result of optimal fertilization, the economic benefits for farmers will improve and will assist in preserving ground water quality especially contamination with nitrates. This research included two experiments. The first was to find optimal nitrogen fertilization for potatoes and the second to determine the optimal type of nitrogen fertilization which gives best profit and minimize nitrates below root zone at the end of growing season (with comparison to its concentration before plantation) was used as indicator of the amount of nitrates leachate in soil which will contaminate ground water. Nitrates were selected as an important pollutant to ground water because of its negative effects on public health especially when its concentration in drinking water is over allowed limits. It is also formed through nitrification when fertilizers are added to any crop. It was found in this experiment that the amount of nitrogen fertilization added to potato affects such as hardness, density, and number of tubers and weight of each tuber. It was found that increasing the amount of nitrogen fertilization increases density, hardness, and number of tubers and weight of each tuber. • Due to the importance of total yield, the relation between total and nitrogen fertilization added was analyzed. It was found that the relation between yield and N - fertilization is a quadratic relation. After analyzing this relation, it was found that the maximum yield for potatoes under the experiment conditions was found when 35 Kg of net N—fertilization were added in the form of ammonium sulfate. Yield at this amount was found to be (4062 Kg / dunum). After analyzing the net profit which farmer gets, it was found that maximum profit will be obtained when (25 Kg / dunum) of net N- fertilization were added in the form of ammonium sulfate (yield will be 4016Kg/ dunum). However, this quantity is highly sensitive to price of potatoes in local markets. • After analyzing nitrate residue in the bottom of the root zone at the end of the season, it was observed that the concentration of nitrates increases significantly when more than 25Kg- N-fertilization were added, therefore, in conditions of light soils overlying ground water aquifers which are close to the surface, the recommended amount of net N-fertilization will be 20Kg/dunum (in form of ammonium sulfate), expected yield will be 3962Kg/dunum. From experiment for the type of N-fertilization, it was found that yield well be less when ammonium sulfate is used compared to other types. Yield was more when urea was used or when ammonium sulfates were mixed with other types such as urea and/or organic acids. (When the same amount of net N- fertilization was used). • It was found that the amount of nitrates left in the soil profile increases when organic acids are added to ammonium sulfate. Therefore, it is recommended to add organic acids to ammonium sulfate during fertilization of potatoes to increase yield and reduce leaching of nitrates.