The effects of applying different commercial, controlled release fertilizers (CRF) as a means of controlling NO3- pollution of groundwater in an irrigated maize crop were tested. The polluting effects of two sources of irrigation water with different NO 3- content were also evaluated. The results showed that conventional agricultural practices are one of the main causes of NO3-aquifer pollution. Excess nitrogenous fertilization occurs because of the lack of soil monitoring to rationalize the fertilizer dosages and because the flood irrigation system, used with the frequency and rates applied, accelerates NO3- leaching. The results also show the inefficient use made of water. An analysis of the results, using the evolution of the NO3- leaching rate, proved to be a more reliable source of information for assessing pollution than the concentrations detected in the soil water solution, below the root zone when the water flow was downwards. The use of two different sources 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 maize growing period owing to the high levels detected in the soil and the 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 of stream and well-water irrigation sources. With Multicote this is only observed with the use of NO3- free water.
