Fertilization of tropical rice: A case study on Bangkok plain

Abstract

This study consisted of a survey on the nutritional status of rice plants in relation to nutrient application and yield in 70 farmers' fields in four provinces of Bangkok plain during the 1977 wet season. In addition a series of fertilizer experiments were carried out on rice experimental stations in the same provinces to study yield response to N and P fertilization and to develop a fertilizer recommendation system based on plant analysis.

The average grain yield in the survey was 3.2 t ha⁻¹ and the early (high yielding varieties), medium (local) and late maturity (local) types yielded 3.3, 2.8 and 3.0 t ha⁻¹, respectively. The average amount of fertilizers applied to these maturity types were 33, 15 and 7 kg N ha⁻¹ and 15, 8 and 6 kg P ha⁻¹, respectively. Regression analysis indicated only a slight correlation between yield and any level of fertilizer application. On experimental stations yields over 6 t ha⁻¹ were obtained with applications of N over 100 kg ha⁻¹ and P over 22 kg ha⁻¹. Evaluation of nutritional status of plants based on plant analysis showed that in all provinces there were strong and widespread nutrient deficiences primarily of N and secondarily of P, and possibly of some other nutrients. Fertilizer application based on plant analysis gave high yield responses. It was concluded that the major constraints of yield on Bangkok plain are too low fertilizer application especially of N, and unbalanced fertilization of N and P.