Use of sulfate fertilizer for increasing rice yield cv. Sakol Nakhon and its effect on soil properties

Abstract

Sulfate (SO42-) is essential for rice growth and grain production. This experiment focused on the influence of the rates of sulfate on rice yield and the components of glutinous rice of cv. Sakon Nakhon. Experimental treatments consisted of 4 rates of sulfate: 0, 100, 200 and 300 kg SO42- ha-1. Ammonium phosphate sulfate was employed (16-20-0, 42% SO42-) as the source of sulfate with two split applications. A silty-clay paddy soil was tested with treatments laid out in RCBD with 3 replications. The results showed that sulfate improved not only the number of complete grain per panicle, but also the percentage of filled grain. Rice yields were not different among sulfate treatments with the range of 7.71-8.41 t ha-1 while those without sulfate gave only 1.9 t ha-1. Sulfate gave more rice straw weight and higher harvest index. After paddy soil was submerged, the pH increased to near neutral. Various ions from the fertilizer dissociate in the soil solution, resulting in higher EC. The contents of organic carbon, total nitrogen, calcium and magnesium in the soil after rice harvest were lower than the values before rice planting. Ammonium, phosphorus and sulfate contents in the soil were highest during the tillering stage (after top dressing application) and decreased with the rice growth stages. The available phosphorus content in the soil decreased throughout the rice growth period. Changes to the mentioned plant nutrients manifested that they are subject to plant uptake; soil microbial assimilation; loss in form of gases from soil, especially for ammonium and sulfate; and leaching of anionic phosphorus and sulfate by water. Besides plant uptake of ferrous, this nutrient was also oxidized in the rice rhizosphere, rendering lower content.