On-farm agronomic manipulations to improve rice (Oryza sativa L.) production in the saline coastal zone of the Red River Delta in Vietnam

Abstract

ABSTRACT Sporadic salinity caused by seawater intrusion is a serious concern for rice (Oryza sativa L.) production in the Red River Delta (RRD) of Vietnam, and guidance for on-farm agronomic management is needed. Three sets of on-farm experiments – namely, trials of (1) nitrogen (N) fertilizer use (replicated trials and surveys of farmer fields, including plots receiving zero N), (2) resistant varieties, and (3) shallow irrigation management – were conducted from 2015 to 2017 in three communes in Nam Dinh province in the RRD, to assess technologies adaptable by farmers. Yield response to N fertilizer in the farmer fields was generally low and greatly variable, associated with variable N recovery efficiency and internal efficiency, particularly in fields at risk of high salinity in one commune during summer 2015. In the replicated trials, N fertilizer applied at 120–180 kg N ha−1 in spring and 100–150 kg N ha−1 in summer generally produced better yields with higher N use efficiencies than the current high N application rates (219 and 189 kg N ha−1, respectively). Recently developed salinity-resistant varieties M2 and M14 produced almost 50% higher yield than the conventional varieties in very saline at-risk fields. Shallow water-depth management (<5 cm) resulted in grain yields similar to the higher conventional-depth management in the less saline fields, but significantly reduced yields in the more saline fields. These results indicate potential resource-use efficiencies in rice production to better cope with coastal salinity in the RRD. GRAPHICAL ABSTRACT