Enhancing the Nutrient Quality of Compost Produced from Cow Manure and Food Waste Using Indigenous Nitrogen-Fixing Bacteria (Azotobacter chroococcum and Azospirillum brasilense)

Razan Layka^*(1), Mousa Al Samara⁽²⁾, and Omiema Nasser⁽²⁾

(1). M.Sc., Higher Institute for Environmental Research, Latakia University, Latakia, Syria.

(2). Department of Environmental Protection, Higher Institute for Environmental Research, Latakia University, Latakia, Syria.

(*Corresponding author: razanjlayka93@gmail.com ).

Received: 01/04/2026                                 Accepted: 24/07/2026

Abstract

Organic waste recycling through composting represents a sustainable strategy for improving soil fertility while reducing environmental pollution. Bioaugmentation of compost with beneficial microorganisms has recently gained considerable attention as an effective approach for enhancing compost quality and nutrient availability. This study evaluated the effects of two indigenous free-living nitrogen-fixing bacteria, Azotobacter chroococcum and Azospirillum brasilense, isolated from agricultural soils in northwestern Syria, on the physicochemical properties of compost prepared from cow manure and household food residues. Both bacterial isolates were identified using morphological characteristics, Gram staining, selective media, and biochemical tests. Compost was produced through aerobic composting of cow manure and food waste (3:1, w/w) and subsequently inoculated with each bacterial isolate separately. The physicochemical properties of untreated and inoculated compost were evaluated by measuring pH, electrical conductivity (EC), organic matter, total nitrogen (N), available phosphorus (P), and available potassium (K). Data were analyzed using Student’s t-test at the 5% significance level. Both bacterial inoculants significantly improved the nutrient composition of compost compared with the uninoculated control. The greatest enhancement was obtained with Azotobacter chroococcum, which markedly increased total nitrogen, available phosphorus, and available potassium while maintaining suitable pH and electrical conductivity values. Azospirillum brasilense also improved compost quality but to a lesser extent than Azotobacter. These findings demonstrate the potential of indigenous nitrogen-fixing bacteria as environmentally friendly bioinoculants for producing nutrient-enriched compost and promoting sustainable organic waste recycling.

Key words: Biofertilizer; Bioaugmentation; Compost quality; Cow manure; Food waste; Azotobacter chroococcum; Azospirillum brasilense; Nitrogen fixation.

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