EFFECT OF THE AMOUNT AND FORM OF NITROGEN FERTILIZER ON VEGETATIVE GROWTH AND NITROGEN UPTAKE AT MAIN PHENOLOGYCAL STAGES OF SPRINKLER IRRIGATED RICE

In cereal crops nitrogen availability is strictly linked with biomass production and can therefore become a limiting factor for grain yield. The amount and time of nitrogen distribution plays an important role in limiting losses and in increasing nitrogen fraction uptake by plants. In flooded irrigated rice, if the fertiliser is incorporated in the reduced soil layer, the denitrification process is reduced as nitrogen is kept in the N-NH4+ form by the soil exchange complex. With sprinkler irrigation the soil environmental conditions pass from a reduced to oxydated state: under these conditions soil NO3 is formed very rapidly and, not being retained by the soil CEC, is easily leached. The effects of different nitrogen amounts and formulations on vegetative growth and element uptake at main phenological stages was evaluated. Treatments with 100, 150 and 200 kg ha–1 nitrogen supply in ureic, nitric and mixed (ureic and nitric in equal parts) form was compared. The highest values of LAI, particularly at 150 and 200 kg ha–1 nitrogen levels, were recorded in the mixed treatment. A higher nitrogen content in leaves, stems and panicles at main phenological stages was also recorded in mixed treatment. The total amount nitrogen utilised by the crop, at ripening, was highest in the mixed treatment.