SUMMARY Salim Priyatna dan I Gde Ekaputra Gunartha, 2006.-- IDENTIFICATION OF DETERMINANT FACTORS IN THE REACTION OF NUTRIENTS RELEASE FROM SILICATE ROCK IN SOIL. (i – xi; 22 pages)1) The effectiveness of silicate rock fertilizer (SRF) is determined by the rate of dissolution of nutrients from SRF in the soil, which is affected by the properties of the soil. However, which properties of the soil dominantly determine the dissolution has not been known. Such knowledge is important in order to be able to modify, or to identify on what types of soil that the application of SRF will be most beneficial. This research was aimed to identify : (1). dissolution kinetic of nutrients from SRFs in soil and (2). which soil properties significantly determine (e.g. determinant factors) the dissolution rate. Data of this research will be used to construct a model predicting tha capacity of SRF in supplying plant nutrients. This research was conducted in the Laboratory of Soil Chemistry and Biology, Faculty of Agriculture, the University of Mataram. The rock (basalt) was taken from Tambora volcano of Sumbawa Island and K-feldpar from Western Australia, both were ball milled for 10 minutes of basalt and 60 minutes of K-feldpar. The compositions of mineral and total of main elements in the rock were respectively identified by using an X-ray diffraction and a wet digestion method described by Jackson (1958). Dissolution media (synthetic soil) was prepared by mixing : (1). silicate sand, (2). montmorilinitic-clay fraction, (3). kaolinitic-clay fraction (kaolinitic A), (4). kaolinitic –clay fraction that has been extracted for its amorphous constituents (kaolinitic B), and (5). organic acids ( a mixture of citric + oxalic acids). Forty types of dissolution media were provided by combining these materials at ratios of 90, 80, 70% of sand; 0, 10, 20, 30% of clay fraction, and 0, 0.001, 0.005, 0.01% of organic acids. Two sets of experiments were prepared, i.e. 5 g SRF (basalt) + 250 g each dissolution media (40 units) and 5 g SRF (K-feldpar) + 250 g each dissolution media (40 units). An additional 40 units of 250 g-media without SRF were prepared in the same manner, which were used as control treatments. Each of these mixtures was wetted with H2O in a plastic bottle and maintained at moisture content of about 125% of field capacity, and those were incubated in an air conditioned room of 22-25o C. A sub sample was taken from each bottle after 1, 4, and 20 weeks of incubation periods for measurement of pH, EC, quantities of extractable Ca and Si (for SRF-basalt treatment), K and Si (for SRF-feldpar treatments) using 0.01 M citric-oxalic extracting solution. The quantity of element dissolved from applied SRF was calculated from the quantity of extractable elements fro treated sample minus that for control sample. Results indicate that the application of SRF significantly increases the pH but no to little effect to the EC of each dissolution media. The relationship of the quantity of dissolved element with clay content of dissolution media form a general equation of dh = d0 + aLn ( a power equation) which dh is the quantity of dissolved element

Jurusan Ilmu Tanah Fakultas Pertanian Universitas Mataram

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Jurusan Ilmu Tanah Fakultas Pertanian Universitas Mataram

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(cmolc.kg-1) in a media containing L% of clay; d0 is the quantity of dissolved element in a media without clay; a and n are empirical constants; L is % of clay content in the media. The relationship forms for montmorilonitic mixture and those kaolonitic mixture are quite similar. Results of a multivariable analysis for the independent variables of clay type, clay content, and organic acid content in the media indicate that organic acid content is the most dominant factor determining dissolution of element from SRF. The higher organic acid content, the more quantity of element from SRF is dissolved in the media. Based on available data from this research, a model may be constructed: dh = f(organic acid content) + f(clay content). Further researches are needed in order to construct a model that is appropriate to be tested in field condition, by including: (1). internal factors of soil, i.e., combination of solid fractions at wide ranges, soil organic and organic acid contents and (2). external factors (plant and rhyzospher ecosystem). 1)The results of Fundamental Research funded by the Directorate General of Higher Education, Ministry of National Education, Republic of Indonesia, with the Agreement Contract No: 028/SP3/PP/DP2M/II/2006, date on 1st of February 2006.