Development of Biodegradable Coating Formulations for Slow/controlled Release NPK fertilizer
Development of Biodegradable Coating Formulations for Slow/controlled Release NPK fertilizer: towards Smart Fertilizers with high nutrient use efficiency
By Prof. Mounir, EL ACHABY and PhD student Ihsane KASSEM
Fertilizers are materials that contain essential nutrients of the plants such as phosphorus, nitrogen, and potassium. These materials are applied to the soil to increase and maintain agricultural production to meet the demand of the growing world population that is expected to approach 9.5 billion by 2050 . Fertilizers can be classified into organic and inorganic ones; the organic fertilizers are derived from the waste of plants and animals while inorganic fertilizers contain one or more nutrient element in the form of inorganic salts obtained by chemical industrial processes . Since 1920, OCP group is one of the leading exporters of fertilizers in the world. The inorganic fertilizers produced by OCP group include diammonium phosphate (DAP), Monoammonium phosphate (MAP), Triple super phosphate (TSP) and ternary fertilizer made by three major nutrients: Nitrogen, phosphorus, and potassium (NPK).
Problems related to traditional fertilizers
Obviously, the main objective of using fertilizers is to provide nutrients to the plants. However, recent studies on commonly used NPK fertilizers have shown that about 40-70 % of nitrogen, 80-90% of phosphorus and 50-70% of potassium are lost in the environment without being absorbed by plants (Scheme 1) , which causes not only economic losses but also very serious pollution of the environment. The main environmental impacts associated with fertilizer’s application are nitrogen and phosphorus leaching into groundwater, greenhouse gas emissions (nitrogen oxide), pollution of soil and surface runoff of nitrogen and phosphorus.
Scheme 1: Representative scheme to the problems related to conventional fertilizer’s use
Coating of fertilizers is one of the most effective tools for solving major problems related to fertilizers use efficiency. The coating material on the surface of fertilizer granules can act as a physical barrier making the release rate of nutrients slower and gradual to coincide with the plant needs, consequently the plant can take up nutrients for long period. These smart fertilizers are called slow or controlled release fertilizers .
Synthetic polymers which are derived from petroleum oil, have been extensively employed as coating materials of fertilizers. However, the high cost of these polymeric coatings and their complicated production processes limited their industrial production and large-scale applications for slow/controlled release fertilizers in agricultural fields. Furthermore, these petroleum-based synthetic polymers are not biodegradable which means that the polymer residue shells remain in the soil and resist to decomposition after release of nutrients, thus they are potentially harmful to the soil environment . Naturally extracted polymers from biomass remain the best alternative to synthetic polymer coatings as they are produced from natural and renewable resources. These bio-based polymers are biodegradable and low-cost materials since their sources are abundant in nature. Among these biopolymers we cite cellulose, chitosan, starch, keratin, pectin, lignin, and their derivatives. Figure 1 represents one example of coated urea fertilizer using lignin [4,5]
Figure 1: Examples of coated urea fertilizer using lignin and modified lignin-based coating formulations
In MSN department, we have the opportunity that biopolymers and biopolymers-based composite materials for functional applications such as food packaging are always in development. In fact, the production of cellulose is one of the most studied activities in our team at MSN department. Figure 2 demonstrates rious examples of cellulose biopolymers extracted from cellulose-rich bio-sourced materials [5-9]. It is important to use our expertise in biopolymer-based materials, regarding the activity of biopolymers-based materials, especially cellulose-based biopolymer for the development of slow/controlled NPK fertilizers. It is worth noting that the as-extracted cellulose biopolymer has a high ability for the formation of porous films, which is suitable for coating of fertilizers.
Figure 2: Examples of cellulose biopolymers produced from cellulose-rich bio-sourced materials.
These works have been recently achieved at MSN department at UM6P [7,8,9,10,11]
Our work in this project involves the development of slow/controlled release NPK fertilizers to improve their nutrients use efficiency. These smart fertilizers are produced via coating technology using various coating processes such as rotary drum as well as fluidised bed equipment (Figure 3). The coating materials are biodegradable formulations based on natural polymers namely cellulose and its derivatives (hydroxyethyl cellulose, ethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose nitrate, carboxymethyl cellulose) and others.
Figure 3: Coating of fertilizer granules require appropriate formulations and processes.
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