MA65525B1 - Stable organo-mineral amendment based on slag associated with horse manure - Google Patents

Abstract

With the rapid increase in the world population, the steel industry, like other industries, is increasingly concerned about the safe and environmentally friendly recycling of slag. Indeed, the steel industry was designed to produce iron and steel of a specific quality and quantity. In Morocco, more than 1.2 million tons of slag are continuously produced each year without any treatment or recovery. With the rapid growth of industrialization in recent decades, the increase in the volume of slag has led to the occupation of agricultural land with the potential to pollute groundwater and soil, which has drawn attention to the need for more adequate and efficient recycling. Furthermore, the direct application of slag to agricultural soils as an inorganic fertilizer without any prior treatment can be harmful to the environment. In this regard, biotransformation, improving the method and rate of application and spreading of slag is an essential means to enable farmers to protect their soils against contamination and achieve sustainable development. Indeed, the addition of slag as a product composed of a wide range of elements (Fe2O3, CaO, SiO2, MnO, MgO, ZnO, P2O5, and TiO2) to organic manure rich in nitrogen and organic carbon can be both an excellent solution and an essential environmental act to enrich the organo-mineral fraction of poor agricultural soils in arid and semi-arid areas, while limiting the transfer of heavy metals to crops. This patent aims at the biotransformation of organic waste rich in nitrogen and organic matter associated with slag as an innovative process to valorize these by-products and recycle them into stable, efficient and nutrient-balanced organic amendments. In this work, the evolution of the C/N ratio is more pronounced in the windrow (A2) containing 10% slag in association with horse manure with a decrease of 52% compared to the windrow (A1) (containing only horse manure) after six weeks of composting. The final pH was 7.2 and 7.7 for the two composts produced, in accordance with the requirements of national standards. Mineralization and humification of organic matter are greater in the compost containing 10% slag. In addition, the nitrogen and phosphorus content are higher in the windrow A2 with an increase of 46% and 67% respectively compared to their initial state. In addition, after six weeks of the composting process, the content of humic substances (SH) was improved by 37% in the compost containing 10% slag compared to that without slag. Also, the application of SH obtained at different doses (60, 120 and 180 mg/Kg) led to an improvement in various growth, physiological and biochemical parameters of radish. Indeed, the dose of 120 mg/kg of SH significantly improved the fresh weight of the bulbs, especially in radish treated with A2 containing slag and horse manure, by 58.7% compared to plants grown in the absence of SH. A clear improvement in stomatal conductance and chlorophyll fluorescence was noted, especially in radish treated with SH (120 mg/Kg) from slag-based compost. Therefore, SH extracted from slag-based compost can be exploited in the sustainable agriculture sector to improve the quality and productivity of radish crops in degraded and humus- and nutrient-poor soils without any environmental and/or health risks.