Urea briquettes containing diammonium phosphate: a potential new NP fertilizer for transplanted rice

The rapid rise in fertilizer prices over the past 2 years coupled with the notoriously low nutrient recovery of fertilizer by lowland rice as managed by farmers of most developing countries has prompted a re-examination of urea briquette agrotechnology that improves fertilizer use efficiency.Urea briquettes containing diammonium phosphate (UB-DAP) can be cost effectively produced using a portable fertilizer briquetter on a small scale (200 kg^-1 h^-1) at the village level and at a price affordable by small rice farmers. Their improved management consists of hand placement of properly sized (weight) UB-DAP (N:P = 4:1) per briquette for every four rice hills, and at 7–10 cm soil depth, on the day of or the day after transplanting using modified 20 × 20 cm spacing (25 hills m^-2). This management is simple to adopt, saves up to 50% of the labor normally required for its conventional hand placement, and helps to reduce the lag period of spatial nonavailability of DAP-P to the rice plants. Results of several farmer-managed field trials conducted during the 1990–95 wet seasons in India demonstrate that the UB-DAP management makes the fertilizer agronomically more efficient, economically more attractive with less risk, and reduced losses of nutrients as compared with conventional use of prilled urea and single superphosphate. The fertilizer use offers women farmers a unique opportunity to play an important role in increasing rice productivity. The management of UB-DAP can be integrated with plant nutrient recycling and limited Gliricidia green manuring (an agroforestry approach). This integrated use of UB-DAP has the potential to increase rice production of small resource-poor rice farmers with less fertilizer and in sustainable manner in rainfed as well as irrigated transplanted rice ecoregions of developing countries, while protecting the environment. Therefore, the UB-DAP fertilizer can be an important NP source for transplanted rice in the 21^st century.