Comparative Effects of the Application of Prilled Urea and Urea Supergranules on Flooded Rice in Madagascar

Applying urea supergranules to flooded rice (10 cm deep, 3 weeks after transplantation) is associated with yield increases of 17%, 23%, 22% and 16% (for doses of 27, 54, 81 and 108 units of nitrogen per hectare) compared with prilled urea. Nitrogen-15 can be used to establish the real nitrogen utilization coefficients for the aerial parts of the plant. While the figures are very low for prilled urea (between 4% and 9%), they exceed 25% and 38% for supergranules on the sites studied. The effect of fertilizer form is greater than the dosage factor. The results are discussed in terms of apparent utilization coefficients and mechanism used.