Controlled Released Fertilizers (CRFs)

Controlled Released Fertilizers (CRFs)- Enhancing Fertilizer Use Efficiency

The goal of nutrient management is to provide an adequate supply of all essential nutrients for a crop throughout the growing season. If the amount of any nutrient is limiting at any time, there is a potential for loss in production. As crop yields increase and as increasing amounts of nutrients are exported from the fields where crops are grown, the nutrient supply in the soil can become depleted unless it is supplemented through application of fertilizers. A fertilizer is any substance or material that has either natural or synthetic origin and is distributed to the soil or plants to supply plant nutrients that are essential to the growth of plant tissues. Chemical fertilizers offer mainly three important macronutrients, namely phosphorous, potassium, and nitrogen. Fertilizers may also add some secondary nutrients such as sulphur, calcium, and magnesium to the media or soil. Fertilizers need to be applied to all types of crops production systems to achieve the yield levels which make the effort of cropping worthwhile. However, excess or uncontrolled use of fertilizers destroys the soil properties, such as osmolarity and water holding capacity. Excess usage can also adversely affect soil microorganisms.

Effectiveness of nutrient supply and increased nutrient use efficiency with reduced environmental pollution depends on two factors: matching nutrient supply with plant demand and maintaining nutrient availability. One effective method for increasing nutrient use efficiency and minimizing environmental hazards is the use of controlled release fertilizers (CRFs). The term CRFs refers to fertilizer granules that intercalate within carrier molecules and thereby improve the efficiency of nutrient release to the crops and reduce the ecological, environmental, and health hazards. Fertilizers encapsulated in organic or inorganic material have a controlled rate and duration of plant nutrient release. One of such CRFs is polymer coated urea CRFs provide a nutrient release for a longer period as compared to quick release fertilizers. CRFs increased the availability of nutrients due to the controlled release of nutrients into the fixing medium during the fixation process in the soil. They increase the efficiency of nutrient availability and reduce the environmental degradation.

Generally, CRFs are coated with polymers for their controlled release. Polymer can be either natural or synthetic and the nutrients are released from the polymer at a controlled rate. These polymers are biodegradable or nonbiodegradable. Polyvinyl chloride, polyacrylamide, and rubber are examples of synthetic biodegradable polymers. One of the advantages of these biodegradable polymers is the lack of toxicity and biological activity. Control release fertilizers potentially minimize environmental hazards and may improve the nutrient use efficiency. This technology is generally applied to those fertilizers in which the factors dominating the rate, pattern, and duration of release are well known and are controllable during the preparation of controlled release fertilizers.

One of the important factors for the release of nutrients is moisture content. When the growing medium dries off, it can greatly reduce the fertilizer release. It works well at normal temperature in case of crops. At low temperatures ie 10oC, there is no fertilizer release. If the temperature is high ie 32oC, the fertilizer release is excessive. The use of CRFs is associated with several economic, agronomical, and environmental benefits. Economically, it reduces the cost, by ensuring the supply of nutrients to the crops for the entire season through a single application thereby reducing the demand for short-season manual labours. Agronomically, the usage of CRFs is associated with enhancement of plant growth factors such as it reduces the stress and increases the availability of nutrients due to controlled release. In environmental aspects, the CRFs increased nutrient utilization efficiency, thereby reducing the loss of excess nutrients into the environment. High accumulation of fertilizer in the environment is minimized and, as a result, it decreases environmental problems associated with conventional fertilizer use such as eutrophication, which causes the water oxygen depletion, death of fishes, unpleasant odour, etc.

CRFs release the nutrients at a controlled rate or pattern into the soil. It is most used in nurseries to fertilize perennial crops such as oil palm, tree crops etc. The nutrient supply in a controlled manner increases the nutrient use efficiency and reduces environmental hazards. It reduces manual labour demands during critical periods of crop growth and reduces stress and toxicity. Temperature and moisture content are the important factors for the release of the nutrients from granules. The efficient, reliable, and cost-effective CRF minimizes food crises and other challenges of crop production. When compared to conventional fertilizers, nutrient release from CRF minimizes leaching and increases fertilizer-use efficiency.