CONTROL OF NITRATE POLLUTION BY APPLICATION OF CONTROLLED-RELEASE FERTILIZER (CRF), COMPOST AND AN OPTIMIZED IRRIGATION SYSTEM

A nitrogenous controlled release fertilizer (Floranid 32) and a treatm ent of municipal organic waste compost were tested under two irrigatio n managements (conventional and ET-adjusted irrigation rates) with the aim of assessing risk of nitrate leaching to the aquifer. A check wit hout N fertilizer was introduced. The experiment was carried out at La Poveda Field Station (30 km SE Madrid, Spain) in alluvial soils with water table depth at 4 m and under maize cropping. The experiment was laid out in a randomized complete block design with three replications , allocating 12 plots to each irrigation management. Although N fertil izer rate (150 kg ha(-1)) was reduced at half as related to a previous experiment, no difference in grain yields was observed. This result r elates to a high content of soil-N. Floranid showed promising results in controlling N-leaching in comparison with urea that exhibited an ac celerated rate of N release which finally determines low use of N by t he plant and marked NO3- leaching. Treatment of municipal waste compos t showed NO3- concentrations in the soil water solution of similar val ues as those of urea at 140 cm. ET-adjusted irrigation showed no drain age during the corn growing season and lower NO3- concentrations in th e soil water solution which could indicate a general lower rate of N s olubilization.