Agronomic assessment of solar dried recycled olive mill sludge on Maize agrophysiological traits and soil fertility

Authors

• Bouhia Youness ¹
• Karim Lyamlouli ¹
• Yedir Oudouch ^{2, 1}
• El Mehdi El Boukhari Mohamed ^{2, 1}
• Mohamed Hafidi * ^{2, 1}

1. AgroBioSciences Program, Mohammed VI Polytechnic University (UM6P), Benguerir 43150, Morocco
2. Laboratory of Microbial Biotechnology, AgroSciences and Environment, Faculty of Sciences Semlalia, Cadi Ayyad University, Marrakesh 40000, Morocco

Abstract

Purpose Olive mill waste sludge (OMWS) is a solid by-product resulting from olive oil extraction, OMWS is usually left decanting in landfills causing environmental pollution and a significant loss of recyclable organic resources. This study aims to evaluate the feasibility of producing an organic amendment through treating OMWS with solar drying (SDy), which is a low-cost method, highly adapted to semi-arid and low-income countries.
Method We investigated the effect of 90 days SDy on OMWS physico-chemical properties, then the agronomic efficiency of the resulting product was assessed under greenhouse conditions, using Zea mays as a crop model.
Results The SDy treatment significantly reduced OMWS initial moisture and the C/N ratio, while the nutrient content of the final product was improved. Pot trial under greenhouse conditions revealed that the application of SDy-OMWS improved the soil physico-chemical properties. The initial application decreased soil pH from 8.19 to 7.06, and soil phosphorus (P), potassium (K), iron (Fe) and zinc (Zn) increased by 209%, 162.4%, 290% and 270% respectively compared to the unamended control. SDy-OMWS application initially induced a delayed seed germination and plant growth at early stages, which was followed by a significant improvement of plant above and below ground traits, including photosynthetic activity, stomatal conductance, and root parameters (RL, RSA and RV).
Conclusion Overall, SDy significantly reduced the C/N ratio, moisture, and improved the nutrient content of OMWS. Despite improving soil fertility, SDy-OMWS application negatively affected the plant development at early stages. However, such effect was completely alleviated at the end of the experiment.

Highlights

• Nitrogen-fixing bacteria biologically fixes atmospheric nitrogen in natural and cropped systems.
• Organomineral fertilizers are improving crop performance, resistance and productivity.
• Azospirillum brasilense and Bradyrhizobium japonicum enhanced soybean proline activity.
• Soybean protection was improved when brasilense and B. japonicum were co-inoculated.
• Organomineral fertilizer is an efficient inoculant carrier for brasilense in soybean plants.

Keywords

• Microorganisms
• Olive mill waste sludge
• Organic amendment
• Plant development
• Soil Toxicity