Composting date palm residues promotes circular agriculture in oases

Abstract

Dry leaves of date palms (DPs) are by-products of date cultivation that are often mismanaged in oasis agroecosystems. Ideally, they should be upcycled in a circular agriculture model before producing and exporting high-value products. Compost inputs enhance soil organic matter and conserve soil. This study investigated composting of four mixtures based on farming system requirements and the availability of organic resources. The DPs were used alone or combined with sheep manure and rock phosphate. We experimented with farm-scale windrow composting to improve understanding and support decision-making. The results showed that temperature increased rapidly to 70 °C at the beginning of composting in the mixtures with manure. Organic matter content decreased by 40% in all windrows during composting, which indicated organic matter mineralisation and loss of volatile solids. Composting DP with or without sheep manure for 136 days with two turnings conserved nitrogen and increased the nitrogen content of compost. Mixing DP with sheep manure and rock phosphate increased the final total phosphorus content of compost to 0.52% (dry matter basis). Our results highlight that composting DP is a feasible alternative to improve circularity in oasis agroecosystems, by increasing organic matter content and fertiliser value, thus paving the way for sustainable production of high-value products from DP.