Long-Term Effects of Sulfur and Zinc Fertilization on Rice Productivity and Nutrient Efficiency in Double Rice Cropping Paddy in Bangladesh

Sulfur (S) and zinc (Zn) deficiencies are frequently reported in Bangladesh rice paddy. However, its effects on rice productivity and soil fertility need to be reevaluated as sulfur oxides (SOx) and heavy metals are increasingly emitted to the environment in the recent years. To examine the long-term effects of S and Zn fertilization on rice yield and nutrient efficiency, the standard fertilization plot of nitrogen, phosphorus, potassium, sulphur, and zinc (NPKSZn) was installed in a typical double rice cropping paddy at the Bangladesh Rice Research Institute (BRRI) farm in 1985. The recommended treatment (NPKSZn) and the comparison treatments (NPKZn and NPKS) were selected for calculating S and Zn efficiencies. The same levels of chemical fertilizers in NPKSZn treatment were applied with the rates of N-P-K-S-Znas80-25-35-20-5kgha(-1) and 120-25-35-20-5kgha(-1) in the wet and dry seasons, respectively. The changes in rice productivity, as well as S and Zn fertilization efficiencies, were monitored for 23years. Sulfur fertilization significantly increased the mean grain and straw yields by around 13% in the wet season and only 4-5% in the dry season. The mean S fertilization efficiencies were 9.3% and 5.3% in the wet and dry seasons, respectively. Sulfur fertilization efficiency was relatively high until 1997 (the 13th year after the installation). Thereafter, however, S fertilization did not increase rice productivity or efficiency, regardless of the season. Also, Zn fertilization did not result in a significant increase in rice productivity, and its fertilization efficiency was similar level with a mean of 1.2%, irrespective of the season. This study revealed that S and Zn fertilization may no longer be required to increase rice productivity in Bangladesh paddy soil due to fast industrialization and urbanization.