Environmental Hazards and Agronomic Benefits of Organic and Inorganic Nitrogen Fertilization to Sandy Soils Monocropped with Radish. المخاطر البیئیة والفوائد الزراعیة للتسمید النیتروجینی العضوی وغیر العضوی للأراضی الرملیة المزروعه بالفجل.

Abstract

Application of organic in combinations with inorganic N fertilizers can supply plants with all necessary nutrients in slowly available forms without environmental pollution. Vegetable field trials were conducted under controlled greenhouse conditions for two successive seasons using radish as a catch crop in order to evaluate environmental hazards and agronomic benefits of applying different combinations of organic and inorganic N fertilizers to sandy soil. Over both seasons of this study, improvements in growth quality parameters of radish plants were in most cases not significantly different at the higher fertilizer application rates of 120 and 180 kg ha-1. This finding indicates that radish response as a catch crop owing to the increasing of fertilizer application rate is subjected to diminishing returns, beyond which further additions will not improve the yield but pollute soil environment.Results of this research showed that, major considerations in applying of inorganic N fertilizers alone on sandy soils monocropped with catch crops are the increase in residual nitrate in soils, the increase in groundwater contamination potentials by nitrate, and the threat of nitrates build-up in plant tissues. Under conditions of this study, high application rates of inorganic nitrogen fertilizer (180 kg ha-1) caused high levels of nitrate accumulation in radish, and on being con­sumed by human beings, pose serious health hazards. In general, at the rate of 120 kg ha-1 equal combined organic and inorganic fertilizers, no health problems could be foreseen to humans or animals from food chain movement of nitrates. From this research it could be concluded that incorporation of combined organic and inorganic fertilizers into sandy soil monocropped with catch crops at the rate of 120 kg ha-1 nitrogen using drip irrigation system was the best management strategy practice to reach optimum agronomic benefits while minimizing environmental and health hazards.