Pathways and determinants of changing nutrient management in lowland rice-based systems of Southeast Asia

Production increases in lowland rice-based systems of Southeast Asia will not be possible without the addition of nutrients. Recent productivity gains were largely based on increasing the use efficiency of the applied nutrients through integrated and site-specific approaches. The adoption of such strategies has evolved differentially in the various country. We need to understand such recent trends, their driving forces, and their effectiveness to harness or leverage them for regional food security and sustainable development. To gain this understanding, we analyzed changes in fertility-related agronomic practices in six representative rice-based production systems of Southeast Asia (three favorable and three marginal sites). We implemented a diachronic survey (comparing the years 2000 and 2018) combined with field sampling and measurements in 1024 rice-producing households and, where applicable, in both dry and wet seasons (3638 complete data sets). We observed that soil fertility management followed similar trends across sites. However, the timing and the extent of changes were location specific, and differed primarily by the favorability/marginality of the site, and farmers’ capability to adopt technological innovations. The irrigated rice double cropping benefitted most from recent technology innovations (hybrid seeds, farm machinery), accelerating the adoption of improved fertility management practices to an aggregated level of up to 75% (mean across the six soil fertility-related management practices) at favorable sites. Most prominent were multiple splitting of mineral N and the application of mineral fertilizers other than N (P, K, Zn). At marginal sites, aggregate changes toward intensification were rather low with 35–55%, and farmers tended to intensify the non-rice component in the system by applying mineral fertilizers and organic amendments to dry season upland crops. A balanced use of nutrients will require the targeting of options to specific extrapolation domains (social-ecological target environments) based on site attributes and farmers’ resource endowment.