Validating a fertilizer recommendation across a diverse cropping environment

One of the major objectives of on-farm research is to test and refine recommendations coming from controlled research conditions to suit the variable conditions met under farmer circumstances. In developing countries, resources available for agricultural research are limiting. Therefore the challenge is to develop methodologies favouring resource-use efficiency and facilitating relatively fast results. At the same time researchers must take advantage of a high level of farmer participation and sample environmental variables suspected of affecting the technology's performance. In this context, ways in which to deal with variability, both in terms of environment as well as in farmer management, become important. To present lessons learned, this case study describes first relevant aspects of the farming system, a brief history of the problem and the resulting experimental program. For illustration purposes, one year of data is presented in detail. This came from a farmer-implemented, farmer-managed test on urea use (30 kg/ha nitrogen) in rice cultivation based on water harvesting. Variation in rice yields has been investigated in order to determine whether known differences in cultivation circumstances (water level during fertilizer application, field position on the slope, rice variety used) warrant refining the recommendation regarding urea use. It is known for example that water height varying at application time can significantly influence the rice crop's response to nitrogen; however, in this investigation urea use proved to be an economically attractive option over the water level range investigated (5-15 cm). Although variable response to urea use due to environmental factors was identified, economic evaluation using Marginal Rates of Return showed that under all conditions urea use was justified. Therefore, the recommendation does not need to be refined, given the assumptions presented. Finally, the sustainability of urea use is discussed, in view of the fact that nitrogen application enhances crop yields and therefore increases the extraction of other crucial plant nutrients.