Improving nitrogen fertilizer efficiency in lowland rice in tropical Asia

Rice production in Asia must increase 2.2–2.8% annually to keep abreast of increasing population. Greater fertilizer use and crop intensification together with varietal improvement and investment in irrigation will all contribute to increased rice supply. Because fertilizer and input prices have risen faster than the price of rice, increasing fertilizer N efficiency will be a major challenge for rice researchers and farmers. Greater fertilizer N efficiency may be achieved through improved timing and application methods, and particularly through better incorporation of basal fertilizer N without standing water. Other promising alternative practices are use of N-efficient rice varieties, hand or machine deep placement of urea supergranules, and use of slow release N fertilizers. Research challenges include development of placement machines for prilled urea and identification of cost-efficient nitrification and urease inhibitors. Under the present resource-scarce situation in many tropical Asian countries, several complementary practices must be followed to supplement inorganic N sources. Fertilizer supplies and proper price support should be maintained and wherever possible increased, and appropriate fertilizer materials and application methods must be devised to increase N use efficiency in lowland rice, so that increasing rice requirements are fulfilled.