The pH and available phosphorus as primary drivers of compost-induced CO ₂ emissions from Malaysian tropical soil: empirical relationships

Confronting the global need for climate-smart agriculture, this study investigated the major factors controlling CO2 emissions from a Malaysian tropical soil amended with four composts. The cumulative CO2 emissions followed the descending order: chicken dung compost (CDCS) > sludge compost (SLS) > goat manure-leaf compost (GLCS) > food waste compost (FWCS). Multiple regression analyses identified soil available phosphorus (AP) and pH as the key interactive drivers of CO2 emissions. The significantly higher emissions from CDCS were primarily due to its pronounced elevation of soil pH, likely stimulating microbial activity. The positive correlation with AP indicated that enhanced phosphorus availability further promoted microbial carbon mineralization. The findings demonstrate that compost is not a carbon-neutral amendment; its net climate impact depends on the specific physico-chemical changes it induces in the soil. This provides a scientific basis for optimizing compost selection to reconcile soil fertility improvement with greenhouse gas mitigation in tropical agroecosystems. In this experiment, four composts (FWC, GLC, CDC, SL) were applied at 2.5 % and 10 % rates to typical Malaysian tropical soils and incubated for 90 d. The CO2 emission characteristics were measured in different soil types. To determine key drivers, the study examined correlations between soil physico-chemical properties and CO2 emissions and selected the relative important factor.