CONTROLLING NITRATE POLLUTION OF AQUIFERS BY USING DIFFERENT NITROGENOUS CONTROLLED-RELEASE FERTILIZERS IN MAIZE CROP

The effects of applying different commercial, controlled release ferti lizers (CRF) as a means of controlling NO3- pollution of groundwater i n an irrigated maize crop were tested. The polluting effects of two so urces of irrigation water with different NO 3- content were also evalu ated. The results showed that conventional agricultural practices are one of the main causes of NO3-aquifer pollution. Excess nitrogenous fe rtilization occurs because of the lack of soil monitoring to rationali ze the fertilizer dosages and because the flood irrigation system, use d with the frequency and rates applied, accelerates NO3- leaching. The results also show the inefficient use made of water. An analysis of t he results, using the evolution of the NO3- leaching rate, proved to b e a more reliable source of information for assessing pollution than t he concentrations detected in the soil water solution, below the root zone when the water flow was downwards. The use of two different sourc es of irrigation water (well, 43 mg NO3- l-1 and stream, 3 mg NO3- l-1 ) showed no significant differences on the NO3- leached during the mai ze growing period owing to the high levels detected in the soil and th e high dosages of N applied. In the stream irrigation water experiment , a greater polluting effect was observed with conventional fertilizer application (urea) than with CRF. The results obtained with Floranid 32 showed the effects of control over NO3- leaching both in the case o f stream and well-water irrigation sources. With Multicote this is onl y observed with the use of NO3- free water.