Alleviating soil acidity using basalt for improvement of rice (Oryza sativa L.) yield grown in an acid sulphate soil

Rice yield on acid sulfate soils in Malaysia is low, far below the national average of 3.08 t ha-1 year-1, due to Al and/or Fe (ll) ion toxicity. Acid sulfate soil and sediments contain iron sulfides (FeS2), the most common being pyrite. When exposed to the air due to drainage or disturbance, these soil produce sulfuric acid, which this make, the pH become low (≤3.5). Acid sulfate soil pose chemical, biological and physical problem to the crop. This study was conducted to ameliorate an acid sulfate soil in the Semerak- Kemasin Integrated Agriculture Development Project (IADP) located in Kelantan, Peninsular Malaysia, for rice cultivation using ground magnesium limestone (GML), and ground basalt. An incubation study was conducted in the glasshouse to alleviate the infertility of an acid sulfate using basalt with or without ground magnesium limestone (GML). Fresh soils were treated with the amendments and some microorganisms than subjected to two cycles of submergence (4 months) and drying (2 months). After every 4 months of submergence the soil and solution were taken for the analysis. The untreated soil pH was 3.44 (<3.5) and exchangeable Al in the soil was high (5.36 cmolc kg-1). GML application at 4 t ha-1 was able to increase pH and subsequently, reduced Al toxicity for rice growth. After 4 months of submergence, solution pH of the sample treated with 4 t basalt ha-1 had increased from 3.61 to 3.94, with concomitant decrease of Al. In the same cycle, soil pH increase was much higher (5.22). Basalt is thus deduced as comparable to GML as an acid soil ameliorant. Within the experimental period, basalt had mostly disintegrated and dissolved. The solution pH had further increased (5.94)in the 2nd cycle due to dissolution of more basalt. This means that it takes time for basalt to completely dissolve and consequently supply Ca, Mg, K and P to the growing crop in the field. Basalt application is only good for a long- term solution for acid sulfate soil infertility. Another glasshouse study was conducted using the same type of acid sulfate soil in which rice was used as the test crop. This study was conducted in order to determine the effects of applying ground basalt on the chemical properties of an acid sulfate soil and the growth of rice. GML as command amendment used by farmer in Malaysia as a liming material, so that, GML were use to compared the effectiveness of basalt as a liming material. Statistical analysis show there are no significant different between 4 t GML ha-1 (T2= 4.21 t ha-1) and 4 t basalt ha-1 (T4=4.41 t ha-1) on rice yield. The low fertility of the soil can be effectively ameliorated by applying 4 t ground basalt ha-1 and improve the rice yield grown in an acid sulphate soil. This study showed the clear benefit of ground basalt as an amendment for acid sulfate soil infertility. This is comparable to that of applying 4 t GML ha-1, which is the standard lime requirement of acid sulfate soil in Malaysia. Basalt takes time to dissolve completely. The best option is therefore to apply ground basalt in few months before rice is transplanted in the field. Basalt application has other advantage by way of supplying Si needed by rice for its maximal growth. Basalt application had increased solution and soil pH. This resulted in the precipitation Al as Al- hydroxide. Basalt contains Ca, Mg, K, P and S. The dissolution would provide the macronutrients to the growing rice in the pots. Furthermore, the presence of extra Ca in the treated soils had somewhat alleviated Al toxicity. Only N is absent in basalt. The hydrolysis of the silicate released by the olivine not realized carbon dioxide CO2 which is the principal greenhouse gas compared to hydrolysis of CaMg (CO2)2 produce by GML. This excess released of CO2 will promote into climate changes. Though, GML is the best liming material to increased the pH and lowering the Al concentration in an acid sulfate soil, but in other hand, basalt also have a big potential to be another alternative as liming material, basalt as because of the cost is low, RM 30 per ton compared to GML which is RM 165 per ton. Basalt application by famers will reduce the rice plantation cost.

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