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Many researchers have proposed the use of silicate rock fertilizers (SRFs) as alternatives to chemical fertilizers. However, the application of SRFs in modern agricultural practices is limited due mainly to the slow release of plant-nutrient elements from SRFs and consequently many tonnes/ha of SRFs may need to be applied. Simple and inexpensive methods of modifying the physicochemical properties of SRFs are needed to improve the agronomic effectiveness of SRFs. This thesis is focused on the evaluation of high-energy milling to produce superfine particles to improve the effectiveness of mafic (basalt and dolerite) and felsic (gneiss and K-feldspar) rocks for use as fertilizers. The ground mafic rocks are for use as Ca and Mg fertilizers and the ground felsic rocks as K fertilizers. Laboratory and glasshouse experiments were conducted with several potential SRFs. In laboratory experiments, initially milled rocks (Ø < 250 μm for basalt, dolerite, and gneiss; Ø < 150 μm for K-feldspar) were further milled with a ball mill (Spex-8000) for 10, 30, 60, 90, and 120 min under dry and wet (rock/water ratio = 1/3) conditions. To investigate possible reaction between constituents, other subsamples of initially milled basalt, dolerite, and gneiss were added to reagent grade NaCl or KCl (4.5 g rock + 0.5 g NaCl or KCl) and milled for 120 min under dry and wet conditions. Basalt and dolerite were also mixed with K-feldspar at a ratio of 1 : 1 and milled for 120 min under dry and wet conditions. For use in the glasshouse experiment, the initially milled rocks were further milled with a vertical stirred ball mill for 1 h in a dry condition. The elemental and mineralogical compositions of the SRFs were determined using XRF and XRD. Effects of milling on major physicochemical properties of milled rocks were determined, including particle size (Malvern Mastersizer), surface area (BET-N2), quantities of amorphous constituents (XRD, oxalic acid-oxalate extraction, TEM), extractable cations (1M CH3COONH4 pH 7), pHH2O, and electric conductivity. Dissolution kinetics in 0.01M acetic-citric acids (for 56 days) and soil (for 10 months) were determined. Based on the results of these laboratory experiments, a glasshouse experiment was carried out for 12 months to evaluate the effects of SRF application on growth and nutrient uptake of ryegrass grown on several soils. Milling reduced particle size, enhanced amorphism, and increased the release of structural cations from the rocks, with the effects due to dry milling being greater than for wet milling. The optimum milling times which produced maximum amounts of exchangeable cations (Na, K, Ca, and Mg) were 30 - 90 min, depending on rock type. The use of NaCl and KCl as milling additives did not enhance the properties of the SRF. These effects of milling on properties of SRF enhanced the extent of dissolution of SRFs in 0.01M acetic-citric acid and in the soil. More amorphous and/or structurally disordered materials than crystalline materials were dissolved in both dissolution media. The proportion of rapidly dissolved elements, which may be considered to be plant-available, was increased by milling, i.e., from about 2 % (for initially milled rocks) to 70 % (for 120 min dry-milled rocks) of total content, with this proportion for monovalent cations (Na and K) mostly being 2 – 3 fold higher than for divalent cations (Ca and Mg). Incubation of SRFs in soils provided a significant liming effect with a minor salinity effect. The extent of dissolution of SRF in the soil could be accurately predicted by the SRF dissolved in acetic-citric acid in 1 h. Neither SRF nor soil properties were highly predictive of dissolution of basic cations from SRFs in soils, although equations including % sand, % clay, and exchange acidity of the soils are quite predictive of dissolution. The application of Ca in basalt and dolerite SRFs at the rates of 333 – 1332 mg of total Ca/kg soil (≈ 4 – 16 t SRF/ha) greatly increased plant yield and Ca uptake of ryegrass grown on highly acidic and/or Ca deficient soils, but did not do so for plants grown on less acidic and/or relatively Ca-rich soils. The large effects on plants were due mainly to the increase in soil pH rather than Ca supply from the SRFs. Thus the application of these SRFs at much lower rates (≈ 0.2 – 1 t SRF/ha) as Mg fertilizers had only minor effects on pH and consequently on plant growth and nutrient uptake. The applications of milled gneiss at rates of 225 – 1332 mg of total K/kg soil (≈ 25 – 100 t SRF/ha) and K-feldspar (5 – 20 t/ha) greatly increased plant growth and K uptake on soils deficient in K. Milled gneiss was nearly as effective as K2SO4 for use as a K fertilizer based on total content of K in dry tops of plants, but K-feldspar was not effective. However, much of the K2SO4 had been consumed by plants and also these high application rates of K-SRF caused a large confounding effect due to the increase in soil pH which affected the internal efficiency of K in iii producing increased yield. It is apparent that milling greatly improves the effectiveness of silicate rocks for use as fertilizers, thus high-energy milling may be used for manufacturing effective SRF. Results of this research were mostly consistent with pioneering findings by other researchers which found that SRFs may be effective soil ameliorants. SRFs are multi-nutrient fertilizers (including Si) and SRFs are effective liming materials. The multiple beneficial effects of SRFs were greatly improved by high-intensity milling of the SRFs. However, further research is needed to identify optimum and inexpensive milling methods for use at an industrial scale. The effectiveness of milled-silicate rocks as a multi-nutrient fertilizer under field conditions for various soils and plants, a liming material, and a salt neutralizer, should also be determined.

Item Type: Thesis (S3)
Keywords (Kata Kunci): silicate rock, high-energy milling, multi-nutrient fertilizer
Subjects: S Agriculture > S Agriculture (General)
Divisions: Fakultas Pertanian
Depositing User: Ir. Joko Priyono M.Sc., Ph.D
Date Deposited: 05 Aug 2022 02:07
Last Modified: 05 Aug 2022 02:07

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