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.

Nitrogen balance studies in rice using 15N-labelled urea and urea supergranules

Recovery of applied nitrogen by the rice crop is invariably low, often 30–50% (Prasad & De Datta 1979). The poor recovery has been attributed to different types of losses occurring in the rice field. Recovery improved with split application, delayed application or deep placement (Pillai & Vamadevan 1978; Craswell & Vlek 1979), indicating that the management factor plays an important role in increasing fertilizer nitrogen efficiency. To investigate such factors, and seasonal effects, field experimentswere carried out using 15N-labelled urea (PU) and urea supergranules (USG). The recovery of fertilizer 15N by the plant and retention in the soil were studied in both dry and wet seasons.

Fertilizer–use efficiency of amended urea materials in flooded rice

summaryIn a field experiment on a typic hapludoll in 1983 and 1984, deep placement of urea supergranules at 40 and 80 kg N/ha proved to be the best N source, of five tested, for grain production, but at 120 kg N/ha it was similar to neem-cake-coated urea. The results showed that deep placement of urea supergranules can save fertilizer use by 60% compared with prilled urea to obtain the same yield. Shellac-coated urea and dicyandiamide-coated urea was more effective than prilled urea in 1984. Differences in dry-matter production and grain yield were directly related to N uptake by the plants. On average, apparent recovery of applied N increased from 35% for prilled urea to 55, 52·5,46·5 and 37·5% for urea supergranules, neem-cake-coated urea, shellac-coated urea and dicyandiamide-coated urea, respectively.