How to Reduce Chemical Fertilizer? Way forward for sustainable crop production

14 September 2015 06:30 pm - 0 - {{hitsCtrl.values.hits}}

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Human activities worldwide have been recognised as the principal contributor to environmental pollution and climate change that is driving global biodiversity towards extinction. The alarming increase in the oceanic dead zones during the past few decades is a clear indicator of this trend. Among the major causes attributed to such pollution is the widespread use of chemical (reactive) fertilizers. A resolution has been passed at the 2012 UN Conference on Environment and Development (Rio + 20) to reduce the use of chemical fertilizer by 20% by the year 2020.

The use of chemical (synthetic) fertilizer is a standard practice in modern -day high input agriculture. Such inputs without doubt boosted food production to meet the growing demand of an increasing world population and ward off large sale-starvation. Nonetheless, continuous and indiscriminate use of chemical fertilizers often in excess of requirements has not only made food production too costly (particularly for developing countries) but also increased environmental pollution to alarming levels and directly contributed to the aggravation of environmental health problems. The UN publication Global, Environmental Year Book 2003, stated that more than 160 million metric tons of N-fertilizer ends up in the oceans annually and this has doubled the ocean’s dead zones (anoxic areas without aquatic life) since 1990. A more recent publication UNEP Year Book 2014 states that the 150 dead zones reported in 2003 have now increased to 500 dead zones! Usually such dead zones are located near coastal areas associated with high anthropogenic activities and large effluent discharges to the oceans including fertilizer wash-offs.

For example, the Mississippi River basin in Central US drains runoff from the agricultural heart of the North American continent and this nutrient-laden runoff is released into the Gulf of Mexico where a plume of algae and plankton grows explosively. The decomposing organic debris from the plume consumes so much dissolved oxygen that 20,000 km2 of the Gulf becomes hypoxic (unable to support life) each summer. This is the ‘Gulf dead zone’. More recently (May 13, 2015) a team of German and Canadian marine biologists has witnessed for the 1st time a dead zone even in the deep mid Atlantic Ocean, indicating that dead zones could spread even to deeper waters.

In Sri Lanka Dr. Sarath Amarasiri (a former Director-General of Agriculture) has recently published a book Caring for Water in which he describes how excessive application of phosphate fertilizer has significantly increased the P content of four major irrigation reservoirs in the North Central Province where an alarming increase of chronic kidney disease of uncertain etiology is prevalent, particularly among the farming communities. Furthermore it is stated that such P loading leads to the eutrophication of these water bodies resulting in the formation of toxin-producing cyanobacterial (algal) blooms. Therefore it has become imperative that efforts are directed towards the reduction of chemical fertilizer use without compromising on crop yields.

The resolution made by world leaders at the (Rio + 20) conference to reduce the annual use of chemical fertilizer by 20% by 2020 that could save US$ 50 – 400 billion per year in terms of improvement to human health, climate and biodiversity. It has also been reported that the value of nitrogen fixed annually by legumes in Australia is equivalent to three billion Australian dollars.

Therefore both on economic and ecological considerations it has become imperative that we look for alternative inputs for agriculture and food production without compromising on crop yields. This has renewed interest in the efficient use of organic matter including the re-cycling of crop residues and enhancement of natural processes such as biological nitrogen fixation, improving phosphorus uptake through mycorrhizae and increasing beneficial root associated microorganisms of agricultural and pasture crops. However, it should be realized that microorganisms play a critical and vital role in all these alternatives to reduce the use of chemical fertilizers. This article reveals studies so far carried out at the National Institute of Fundamental Studies (NIFS), Kandy on research and development of microbial inoculants for crop production and their potential in minimizing the application of chemical fertilizers in Sri Lanka.

Rhizobial biofertilizer
The status of soil microbiology in crop production in Sri Lanka is rather infantile compared to studies conducted in many other countries. An attempt to introduce rhizobial inoculant technology for soybean (Glycine max) cultivation in Sri Lanka through a FAO/UNDP project (1976 - 1984) did not continue

beyond the project period due to the absence of a low cost, locally available carrier material for transport and storage of inoculants under farmers’ conditions. This limitation was overcome by the findings at the NIFS in 1999 of the suitability of modified coir dust as a carrier material. This breakthrough enabled the field testing and eventual introduction of inoculants to soybean farmers in 2007. Today around 10,000 acres of soybean is cultivated per season with coir dust -based rhizobial inoculants prepared by the NIFS that can completely replace the use of urea fertilizer.

Inoculants for vegetable beans (Phaseolus vulgaris) and mung bean (Vigna radiata) have given positive results and these are about to be released to farmers. Formulation and initial testing of inoculants for cowpea (Vigna unguiculata) and groundnut (Arachys hypogea) are in progress.

Another area of research that has commenced for the 1st time in Sri Lanka is the formulation and field testing of rhizobial inoculants for pasture legumes.
Studies carried out during the last one year have shown the potential of these inoculants to replace the application of urea completely to white clover (Trifolium repens) at Ambewela Farms, Ambewela. These studies are currently being repeated to establish their reproducibility prior to formulating recommendations.

Bio-film Biofertilizers
Rhizobial inoculants can replace only nitrogen fertilizer and they are also confined to leguminous food and pasture crops. However there are a number of non-leguminous crops including cereals (vital to national nutrition) on which large amounts of synthetic fertilizers (N, P, & K) are used. Besides rhizobia, mycorrhizae are used to enhance phosphorus uptake by plants and microbial preparations are sometimes used as bio-control and soil conditioning agents. Such usage of microorganisms is not yet practised on an agronomic scale in Sri Lanka.

Studies conducted during the past decade at the NIFS led to the development of inoculants of microbial communities or microbial consortia which were introduced to the world for the first time as Biofilm-Biofertilizers (BFBFs).

They were found to be more effective than conventional biofertilizers. Application of BFBFs together with low levels of chemical fertilizers has been field -tested on a number of crops in several locations and found to be able to replace 50% of all three (N, P & K) chemical fertilizers in tea, rice, maize and a number of vegetables without compromising on their yields.

These field trials have confirmed that consortia of beneficial microorganisms improve nutrient uptake by plants through increased root growth and activity, rhizoremediation, soil moisture conservation, reduced transpiration and re-establishment of beneficial rhizosphere microbial communities.

Realizing its responsibility in mitigating environmental health problems due to the indiscriminate use of chemical fertilizers, the Government of Sri Lanka has renewed its interest in the development of alternative sources of nutrient supplies for crops. Among them the preparation and widespread application of compost is being popularized, with the President of Sri Lanka playing a lead role in this new venture. It should however be realized that the application of compost may not have the expected impact on the yields of short-term crops like major cereals (including rice), food legumes and vegetables because the release of plant nutrients after decomposition is too slow to meet the immediate demand of such crops. Nevertheless, recent research studies done in other countries (particularly in East Asia) have produced microbial inoculants aptly termed as Effective Microbial Inoculants (EMIs) that could accelerate the decomposition of organic matter including compost. It is imperative that similar studies on research and development of local EMIs be undertaken as a priority in order to achieve targeted sustainable, eco-friendly crop production which can minimize the use of chemical fertilizers.

Considering all these recent research and developments and the importance of the application of soil microbial biodiversity in food production in Sri Lanka, it has been proposed to set up a National Culture Collection of Microorganisms at the NIFS as a repository of microbial germ plasm that will be available for all microbiological research and development activities. It is the responsibility of the new government to use these innovative discoveries to combat chemical fertilizer in Sri Lanka to save the suffering people and the polluted environment of the country.

This article was compiled by Pradeep Piyathilaka, Communication & Media Officer, Science education & Dissemination Unit, National Institute of Fundamental Studies, Kandy after interviewing Prof.S.A.Kulasooriya, Research Scientist, NIFS.

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How to Reduce Chemical Fertilizer? Way forward for sustainable crop production

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