Field-specific difficulties for transplanted rice to cope with ammonia from a localized enriched environment

Abstract

The objective of the study was to find some relationship between the location of rice fields in a typical valley of central Madagascar and the response of transplanted rice to nitrogen fertilizer. Comparison was made between lowland locations and plain location. High rainfalls are typically occurring during the periods of soil puddling and rice transplantation. As a consequence, it is difficult to manage nitrogen fertilization of the crop. To avoid nitrogen losses by runoff, urea deep placement (2 g urea-supergranules at 10 cm depth) was practiced. Probes attached to urea super-granules enabled to observe the dynamics of the ammonia derived from the fertilizer. These observations were performed in three fields (different location). The response of transplanted rice to nitrogen was weak in the lowlands, and rice performed badly in ammonia uptake. In the adjacent plain, the response was better and ammonia correctly assimilated. Ferrous ion toxicity and low phosphorus status are discussed as causes for the rice difficulty to benefit from an ammonia enriched environment in the lowland fields.

Keywords: Lowland, urea super-granule, Madagascar, nutritional disorder, ferrous toxicity.