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Aim: This study was carried out to ameliorate acid sulphate soil (ASS), improve soil nutrient content and the soil quality by employing the use of organic and reduce mineral fertilisation.

Study Design: Treatments were arranged according to a completely randomised block design, in triplicates in a greenhouse.

Methodology: Three fertiliser regimes at three doses (mineral N, P, K (MIN-control (CK), NPK,2NPK), empty fruit bunch compost (COM-CK, EFB, 2EFB) and poultry manure (MAN-CK, PM, 2PM)) were used. The effect of organic and reduce mineral fertilisation on soil pH, nutrient level, microbial count (colony forming unit (CFU)), microbial biomass (Cmic) and enzyme activity were investigated.

Results: The study revealed that the MAN (PM and 2PM) led to a remarkable increase in bacterial and fungal CFU, Cmic, microbial activity, soil organic carbon (SOC) and nutrient content (N, P and K). MAN also stimulated enzyme activities (β-glucosidase (BG), acid phosphate (ACP) and protease (PRO)), but it did not affect the pH of the acid soil later. Soil pH decreased and NPK and 2NPK were not significant. However, microbial count was decreased significantly at 2NPK compared to the control even though the nutrient level was elevated to some extent. In COM, soil pH and nutrient level increased, but the fungal CFU, Cmic and BG were significantly low. Considering the high heavy metal content of the compost we ascribed these observations to a disturbance from the metal contamination due to high qCO2 values at the end of the study, The effect of dose was most pronounced in MAN and least pronounced in MIN.

Conclusion: Our result suggests that, for amelioration and quality improvement of ASS of tropical coastal agroecosystem, manure fertilisation supplemented with lime or EFB compost (of good quality) could be recommended while maintaining favourable moisture conditions in the soil.