Earthworms are among the most productive workers in a tropical plantation soil. Here is what the research says about supporting them.

Earthworms pass soil and organic matter through their gut, releasing nutrients, improving soil structure and stimulating microbial activity in the process. Populations tend to be higher in soils with good organic matter and permanent ground cover, and can fall sharply in degraded plantation soils under continuous monoculture and heavy synthetic inputs. The difference in soil biological function between these two situations is agronomically significant.

What vermicompost actually contains

Vermicompost is the end product of organic matter processed through the earthworm gut. It is not simply decomposed organic matter. The passage through the gut results in a product with higher microbial biomass, more stable humus compounds, more plant-available nitrogen and a more neutral pH than the feedstock material. A larger share of its nitrogen is in mineral forms (ammonium and nitrate) than in uncomposted materials, so more of it is available to plant roots soon after application.

Nutrient content varies widely with the feedstock and the process, so ask for a laboratory analysis of nitrogen, phosphorus, potassium and micronutrients on a dry weight basis before planning application rates. Vermicompost also contains humic substances, which contribute to the soil structure and water retention benefits that distinguish it from synthetic fertiliser.

What the research shows

A meta-analysis of 68 published studies found that vermicompost increased plant growth and commercial yield on average (Blouin et al., 2019). The gains were largest when vermicompost made up a moderate share of the growing medium and when no mineral fertiliser was applied, and they were smaller when mineral fertiliser was also used. Most of the data came from greenhouse and pot experiments, with herbs and legumes among the strongest responders, so field evidence for plantation crops such as oil palm is much thinner and responses on an estate should be checked block by block.

Soil enzyme activity: why it matters

Soil enzyme activity is increasingly used as an early indicator of soil health in plantation management, alongside the more traditional chemical analysis. Urease, phosphatase and dehydrogenase activities reflect the microbial population's capacity to cycle nitrogen, phosphorus and carbon respectively. Studies of vermicompost application commonly report higher activity of these enzymes. SoilBoost EA, a humic acid soil conditioner, may support the same kind of microbial habitat, making it a complementary option for soils where vermicompost is not available in the quantities needed. CSB Organico provides organic nitrogen and carbon inputs that may support soil biology over successive seasons. Hyacinth Plus, derived from water hyacinth, provides an organic carbon source that earthworms and soil microbes can convert to humus.

What vermicompost is not

Vermicompost is not a substitute for a complete fertiliser programme. The nutrient concentrations in vermicompost are too low to meet the full NPK demand of high-yielding plantation crops at economically practical application rates. It is a soil biology and organic matter intervention, best understood as something that makes the rest of the fertiliser programme work better, not something that replaces it.

The EFB connection for palm estates

Palm oil mill residues such as empty fruit bunches (EFB), pressed fibre and mill effluent are abundant organic materials in Malaysian plantation landscapes. Mill residues have been studied as vermicomposting feedstocks, for example mixtures of palm oil mill effluent and palm-pressed fibre (Rupani et al., 2019). At estate scale, the logistics require proximity to a mill, a consistent feedstock supply and careful control of moisture, so the case for an estate vermicompost unit has to be worked out for each mill and estate.

References

1. Blouin, M., Barrere, J., Meyer, N., Lartigue, S., Barot, S., & Mathieu, J. (2019). Vermicompost significantly affects plant growth. A meta-analysis. Agronomy for Sustainable Development, 39(4), 34. https://doi.org/10.1007/s13593-019-0579-x
2. Rupani, P. F., Alkarkhi, A. F. M., Shahadat, M., Embrandiri, A., El-Mesery, H. S., Wang, H., & Shao, W. (2019). Bio-optimization of chemical parameters and earthworm biomass for efficient vermicomposting of different palm oil mill waste mixtures. International Journal of Environmental Research and Public Health, 16(12), 2092. https://doi.org/10.3390/ijerph16122092