In Malaysia, about 0.5 million ha of acid sulfate soils are found scattered over the east, west, and Sabah and Sarawak regions that can potentially be cultivated with paddy. This type of soil is acidic and not immediately suitable for crop production unless improved by applying some amendments. Thus, the current study was carried out to investigate the effects of various types of soil amendments on the growth, yield, and physiological responses of rice grown in extremely acidic conditions using ground magnesium limestone (GML), basalt, biochar, and compost as soil amendments. The acid sulfate soil with a pH of 3.76 was obtained from a paddy field in Merbok, Kedah. The plant responses were evaluated based on agronomic, physiological, and yield performance. The compost-treated rice showed the best performance in all three criteria. Compost treatment increased the soil pH up to 6.25. Physiological performances such as chlorophyll, photosynthetic rate, and water use efficiency were higher after compost treatment, while transpiration and stomatal conductance showed the highest after GML treatment. It can be concluded that the addition of compost as a soil amendment can increase soil pH and create favorable soil conditions for rice cultivation in acid sulfate soil, leading to improved rice growth performance.

A study was conducted at Universiti Putra Malaysia to determine the effect of phosphate‐solubilizing bacteria (PSB) and organic acids (oxalic & malic) on phosphate (P) solubilization from phosphate rock (PR) and growth of aerobic rice. Four rates of each organic acid (0, 10, 20, and 30 mM), and PSB strain (Bacillus sp.) were applied to aerobic rice. Total bacterial populations, amount of P solubilization, P uptake, soil pH, and root morphology were determined. The results of the study showed significantly high P solubilization in PSB with organic acid treatments. Among the two organic acids, oxalic acid was found more effective compared to malic acid. Application of oxalic acid at 20 mM along with PSB16 significantly increased soluble soil P (28.39 mg kg⁻¹), plant P uptake (0.78 P pot⁻¹), and plant biomass (33.26 mg). Addition of organic acids with PSB and PR had no influence on soil pH during the planting period. A higher bacterial population was found in rhizosphere (8.78 log₁₀ cfu g⁻¹) compared to the nonrhizosphere and endosphere regions. The application of organic acids along with PSB enhanced soluble P in the soil solution, improved root growth, and increased plant biomass of aerobic rice seedlings without affecting soil pH.

Micronutrients, such as zinc (Zn), are essential for the growth and development of a wide range of crops. To overcome Zn deficiency in the soil, Zn-solubilizing bacteria (ZSB) have recently been employed. In the present study, samples from the rice fields in the state of Selangor, Malaysia, were collected to isolate, characterize, and identify the ZSB. A total of 88 strains were isolated, and only 9 strains were able to solubilize the insoluble Zn on zinc oxide (ZnO)-, zinc carbonate (ZnCO₃)-, and zinc phosphate (Zn₃(PO₄)₂)-amended Tris-minimal media agar and broth assays. The highest Zn solubilization (20.99%) was measured for the TM23 isolate when exposed to Zn₃(PO₄)₂-modified media culture, whereas ZnCO₃ showed the lowest (3.35%) Zn solubilization by ZSB. In addition, nine isolated ZSB also exhibited plant-growth-promoting (PGP) traits, including nitrogen fixation ability, siderophore production, indole acetic acid production (35.28–65.48 mL⁻¹), phosphate solubilization (27.69–77.38%), enzyme hydrolysis, and production of organic acids. Most of the isolated strains (88) were Gram-negative, except for TM54, which was Gram-positive. The four potential ZSB isolates based on 16RS rDNA sequence analysis were identified as Serratia sp. and Acinetobacter sp. Hence, this study’s findings suggest that these isolates could be prospective candidates to overcome Zn deficiencies and reduce the consumption of chemical fertilizers in agricultural areas.

A study was conducted to determine the efficacy of applying ground magnesium limestone (GML) or ground basalt in combination with bio-fertilizer to sustain rice production on an acid sulfate soil in Malaysia. Soils from Kelantan Plains, Malaysia, were treated with GML, ground basalt, bio-fertilizer, GML + bio-fertilizer, and ground basalt + bio-fertilizer (4 t·ha⁻¹ each). Results showed that soil fertility was improved by applying the soil amendments. GML and basalt contain some Zn and Cu; thus, application of these amendments would increase their contents in the soil needed for the healthy growth of rice. Basalt applied in combination with bio-fertilizer appeared to be the best agronomic option to improve the fertility of acid sulfate soils for sustainable rice production in the long run. In addition to increasing Ca, Mg, Zn, and Cu reserves in the soil, water pH increased and precipitated Al³⁺ and/or Fe²⁺. Ground basalt is cheaper than GML, but basalt dissolution in the acidic soil was slow. As such, its ameliorative effects could only be seen significantly from the second season onwards. The specially-formulated bio-fertilizer for alleviating the infertility of acid sulfate soil could also enhance rice growth. The use of the bio-fertilizer fortified with N₂-fixing bacteria is a green technology that would help reduce NO₃⁻ and/or NO₂⁻ pollution and reduce the cost of rice production. The phosphate-solubilizing bacteria (PSB) present in the bio-fertilizer not only increased the available P, but also helped release organic acids that would inactivate Al³⁺ and/or Fe²⁺ via the process of chelation.

A study was conducted to evaluate the effects of applying rice husk biochar (RHB) or ground magnesium limestone (GML) in combination with bio-fertilizer on soil biochemical properties and the yield of rice planted on an acid sulfate soil. The RHB or GML plus bio-fertilizer were applied each at the rate of 4 t ha⁻¹. Applying the amendments increased soil pH (>5.0) and improved soil biochemical properties with a concomitant reduction of Al and Fe that resulted in enhanced rice growth. Applying GML plus bio-fertilizer resulted in increased soil N content (0.20%), available P (34.38 mg kg⁻¹), exchangeable Ca (2.97 cmol_c kg⁻¹) and exchangeable Mg (2.45 cmol_c kg⁻¹); all these enhanced rice nutrient uptake. The highest bacterial population of 8.34 log₁₀ CFU g⁻¹ soil was found in the same treatment. Applying GML and RHB alone, or in combination with bio-fertilizer, was found to enhance rice growth and the yield. The highest plant height (90.33 cm), leaf chlorophyll content (38.05), plant tiller numbers (16), filled grains (86%), number of panicles per plant (18), lengths of panicles (24.40 cm), grain (5.24 t ha⁻¹), straw yield (10.20 t ha⁻¹) and harvest index (0.51) were determined in the GML plus bio-fertilizer, followed by RHB plus bio-fertilizer treatment. Thus, GML applied in combination with bio-fertilizer is considered as a promising agronomic package to sustain the production of rice planted on acid sulfate soils.

Rabileh, M. A., Shamshuddin, J., Panhwar, Q. A., Rosenani, A. B. and Anuar, A. R. 2015. Effects of biochar and/or dolomitic limestone application on the properties of Ultisol cropped to maize under glasshouse conditions. Can. J. Soil Sci. 95: 37–47. Ultisols in the tropics are characterized by low pH and high exchangeable Al. Maize grown on them produces low yield. A study was conducted to determine changes in soil properties and their subsequent effects on maize growth, resulting from oil palm empty fruit bunch (EFB) biochar and/or dolomitic limestone application. The results show that the application of the EFB biochar improved soil fertility by increasing soil pH. The Al³⁺ activities in the soil solution decreased exponentially with increasing rate of the biochar application. The decrease in Al in the biochar-treated soil occurred because: (1) at the rate of>5 t ha⁻¹, soil solution pH increased significantly, precipitating Al as gibbsite; and (2) the biochar was able to fix some of the Al by chelation. Application of the biochar alone or in combination with lime significantly improved maize growth. The critical Al³⁺ activity for maize grown on Ultisol was 10 µM, while critical pH was 4.7–4.8. Maize grown on the EFB biochar-amended soils produced greater root length compared with that of the control. The optimal rate of EFB biochar application to improve the productivity of the Ultisol for maize production under glasshouse condition was 5–10 t ha⁻¹.