June 23, 2022

Efficient production and use of liquid organic fertilizer

By Sudeepa Lakshan

Fertilizer application is essential for maximizing crop yield. When harvesting a crop, nutrients taken from the soil are removed. Therefore, when continuing cultivation in a field, nutrients for plants must be added outside. Nutrients are supplied by fertilizers. There are different types of fertilizers and liquid organic fertilizers fall into these categories. Liquid organic fertilizers are formulated with materials of biological origin to exist in liquid form. For the effective use of liquid organic fertilizers, several factors must be taken into account, from production to application.

There are different types of liquid organic fertilizers (eg, digested organics, compost tea, vermiwash, and biofertilizers). In all types, regulation of microbial activity is very important.

Discarded fruits and vegetables, fish waste, leaves such as gliricidium, banana stems and peels, seaweed and any organic matter can be used in the manufacture of organic liquid fertilizers. These materials are mixed with water and digested to produce liquid organic fertilizers. Digestion is aided by adding a mixture of known microorganisms or adding small amounts of fertile soil or compost. When microorganisms are not introduced to the outside, the digestion process takes a long time.

There are two main methods of digestion by which organic liquid fertilizers can be produced: aerobic digestion and anaerobic fermentation. When produced under aerobic conditions, liquid organic fertilizers can be made relatively quickly and the nutrient content is relatively high. The release of toxins and toxic gases as byproducts is also minimized. However, to maintain aerobic conditions, the mixture must be constantly agitated (aerated) during the digestion of organics. Thus, the production of liquid organic fertilizer by this process consumes energy. Therefore, the cost of the fertilizer produced using this method is high. Therefore, manufacturers of organic liquid fertilizers on a small scale often use an anaerobic fermentation approach.

The organic liquid fertilizer called “compost tea” is made by infusing compost into water with or without aeration (aerobic or anaerobic conditions, respectively). Liquid organic fertilizer known as vermi-wash is a separate liquid extraction from vermicompost. It generally has a higher nutritional value than compost tea. It is difficult to produce vermiwash in large quantities and it is more suitable to produce at the scale of the home garden.

Biofertilizers are formulations containing living microorganisms. For some biofertilizers, a liquid-based medium is used as a carrier material.

Regardless of the type of liquid organic fertilizer produced, it is imperative to stop or suppress the microbial activity in the liquid organic fertilizer before packaging them in bottles. Otherwise, the microbes in the mixture will continue to function and release gases due to metabolic processes. These gases will build up inside the containers, building up the pressure and the containers could explode. This explains why bottles of liquid organic fertilizer are exploding these days.

Several methods are used to kill or remove microorganisms before packaging liquid organic fertilizers, with the exception of biofertilizers. These methods include filtering, adding acids, centrifuging and heating. When filtering is practiced, the filters must be fine enough to separate the microbial cells from the liquid and otherwise they are not effective in stopping microbial activity.

Liquid organic fertilizers other than bio-fertilizers can be sprayed on the leaves of crops. Here it is mandatory to dilute with water to the ratio indicated on the packaging by the manufacturer. Otherwise, the leaves can burn. However, liquid organic fertilizers sprayed on the leaves cannot meet the total nutrient requirements of the crop. Therefore, liquid organic fertilizers are used as sources of additional nutrients along with solid fertilizers (synthetic or organic chemical) in agricultural production.

Liquid organic fertilizers are easier to apply to subsistence commercial home gardens than to large-scale commercial agricultural land. This is because these can usually be prepared at the household level. Another reason is that it is easier to take precautionary measures against large animals (such as cats and dogs) and insects such as flies which are attracted to the smell of liquid organic fertilizers when they are are practiced on a small scale compared to commercial agriculture. It is important to note that the application of organic liquid fertilizer alone as the application of major nutrients is not sufficient to obtain the maximum yield from a crop.

It is also important to follow hygienic practices when applying liquid organic fertilizers. These fluids can produce highly toxic substances such as phenol, cyanide, and cyanuric acid. It is also very toxic to inhale the gases emitted by these containers, especially those subjected to anaerobic fermentation. The gases emitted by these, such as hydrogen sulphide, are several times more toxic than hydrogen cyanide.

Various problems have been reported with organic liquid fertilizer products due to improper quality control, non-application of subject knowledge and high profit motive. Poor quality fertilizers can lead to crop failures, exploding manure containers, poisoning human and soil-friendly organisms, and destroying crops by dogs. Therefore, the careless use of liquid organic fertilizers and the application of those which have been prepared without meeting the standards and are of poor quality would lead to adverse side effects for health and the environment in general.

The production of liquid organic fertilizer by aerobic digestion is a solution to some problems. Then, the probability of producing toxic gases is also low. Additionally, most plant pathogenic microorganisms are anaerobic and maintaining an aerobic environment prevents anaerobic organisms from dominating the mixture. Therefore, the application of fertilizers produced by aerobic digestion also reduces the risk of spreading disease to the crop.

Standards are under development for liquid organic fertilizers and biofertilizers. At the same time, standard operating procedures should be developed for the industrial scale production of liquid organic fertilizers. It is urgent to accelerate them. At the same time, awareness of liquid organic fertilizers should be increased among the farming community and potential manufacturers. The production of liquid organic fertilizers can be easily linked to the circulation of resources just like the concepts of circular economy. A political environment should be developed to facilitate this.

Liquid organic fertilizer can be standardized and used as an additional source of nutrients to increase crop productivity on the path to sustainable and environmentally friendly farming systems.

(The author is an undergraduate student of the Faculty of Agriculture, University of Peradeniya. The article is based on a discussion with Dr. Warshi Dandeniya of the Department of Soil Sciences, Faculty of Agriculture, ‘University of Peradeniya)


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