Olive mill residue compost: returning organic matter to the grove
After appropriate composting, olive oil production residues can return to the grove, reusing some harvested carbon and nutrients to improve soil.
From feedstock to mature compost
Residues differ with processing. Two-phase mills produce wet, thick organic material known in Spanish literature as alperujo. High moisture and phenolic compounds make appropriate processing important. Complementary materials help create a stable agricultural product.
Mixtures must provide structure, aeration and balanced feedstocks. Research has used shredded prunings and manures. Transformation requires time and final-product maturity and suitability checks; microscopy provides complementary biological information.
Six years in an olive grove
Antonia Fernández-Hernández and colleagues reported in 2014 on four mature two-phase olive mill waste composts applied for six consecutive years to a Picual grove in Jaén, Spain.
Compared with mineral fertilisation alone, treatments increased soil organic matter and nitrogen, phosphorus and potassium. At the end of six years, fruit oil content was higher while oil quality and composition were maintained or similar.
The reported oil-content increase was about 15% in relative terms on a fruit dry-matter basis. Fruit yield did not differ statistically between treatments.
Our field work
We aim to examine mill residues combined with shredded prunings and other suitable materials, producing mature compost with process and microbiology monitoring following our Soil Food Web School training.