APPLICATION OF SILICATIC ROCKS AS SOURCES POTASSIUM ALTERNATIVES FOR RICE CULTURE HIGHLAND

Abstract

Three greenhouse experiments were conducted, one incubation without plants and two with plants. In the first the objective was to evaluate exchangeable K liberation capacity of five sources of silicate rocks of different particle size to soil and their effect on soil pH. Method used was incubation of 600 g soil plus corresponding 5 t ha-1 of rock material. The objective of second experiment was to evaluate response of rice in terms of grain yield as a function of K rates in the form of silicate rocks (0, 75, 150, 225, and 300 kg ha-1), based on total concentration of each rock material (alkaline breccia, alkaline ultramaphic and phlogopitite). The objective of third experiment was to evaluate influence of proportion mixture of silicate rocks to KCl on rice productivity cultivar Curinga. Experimental design was completely randomized with three, four and six replications in the first, second and third experiments, respectively. Particle size of the material was standardize to <0.03 mm. The KCl and one control treatment without K were used as reference treatments. Silicate rocks capacity to liberate K to soil solution varied according to type of silicate rock and time of incubation. The fractions of 45 and 60 mesh were able to supply more exchangeable K. Alkaline breccia and alkaline ultramaphic rocks were more efficient in K liberation to soil for all fractions and incubation time. However, maximum liberation of K occurred at 90 days of incubation period. Upland rice responded significantly (P< 0.05) and positively to K application in the silicate rock form to grain yield, shoot dry weight and number of panicles per plant. However, response magnitude varied according to silicate rocks. Alkaline ultramaphic showed superiority compared to alkaline breccia and commercial KCl did not differ to K source. Grain yield and shoot dry weight increased significantly as the quantity of KCl increased in the mixture of silicate rocks.