On-farm adaptation of knowledge-intensive nitrogen management technologiesfor rice systems

Efficient use of all inputs is vital to achieve and sustain high crop yield s, maintain resource quality, and minimize environmental pollution. Fertili zer N is one of the major inputs in rice production. Blanket fertilizer rec ommendations do not take into account the high field-to-field variability a nd within-season dynamic changes in indigenous N supply. Since the plant gr owth reflects the total N supply from all sources, plant N status will be a good indicator of N availability to crops at any given time. The chlorophy ll meter (SPAD) and leaf color chart (LCC) are simple, portable diagnostic tools that can measure the crop N status in situ in rice fields to determin e the timing of N topdressing. Such decision aids are useful to vary N appl ication rates to rice crops, based on crop demand and indigenous N supply. Although the chlorophyll meter cannot be owned by individual farmers due to its high cost, it is a practically useful tool for field researchers, exte nsion specialists, and crop consultants who do not have access to well-equi pped laboratories. On-farm, adaptive research is in progress in 3 countries to adapt the chlorophyll meter technique for transplanted and wet-seeded r ice, local cultivar groups, and soil, crop, and environmental conditions. I nitial results indicate that the SPAD threshold value of 35 is good for tra nsplanted rice in dry season. The threshold has to be reduced to 32 for wet -seeded rice in dry season and for all rice during wet season with cloudy w eather and low radiation. Thus, when calibrated with local cultivar groups and crop conditions, it can be used to accurately monitor crop N status and to advise farmers on N topdressing for rice. It can also be used effective ly to verify the adequacy of existing N fertilizer recommendations to rice by the in situ monitoring of foliar N status of crops fertilized with curre nt recommendations and to refine them to further improve N fertilization of rice. The LCC is not as accurate as the chlorophyll meter in determining t he leaf N status in rice crops. However, LCC can be calibrated with the chl orophyll meter to fix the critical color shade for local rice cultivar grou ps and crop conditions. Farmers can, then, use the LCC to qualitatively ass ess foliar N status and adjust N topdressing to their rice crops. Initial f eedback on the use of LCC from farmer cooperators in the Philippines is hig hly encouraging. Both methods are affected by factors such as varietal grou p, plant density, crop stress that causes leaf chlorosis, soil nutrient sta tus, and climate; therefore, they have to be adapted to specific soil, clim atic, and crop conditions. Adequate training is necessary for both extensio n agents and farmers to properly use the new tools for increasing the effic iency N fertilizer use on rice. Wider farmer adoption of the two diagnostic tools discussed in this paper will minimize over-fertilization of rice, in crease profitability, and decrease fertilizer-related pollution of the envi ronment.