Beneficial Microorganisms for Sustainable Agriculture

Abstract

There was a desperate need for food to recover the economy of the 1950s and 1960s. Farmers all over the world were advised to rely on intensive production methods and synthetic pesticide inputs to increase the productivity. No doubt, these chemical-based agricultural practices substantially increased crop yield. However, indiscriminate use of agrochemicals have contributed significantly to the environmental pollution and adversely affected human and animal health. In addition, the increasing cost of these agrochemicals has continued to lower the farmer’s net cash return. The global use of synthetic pesticides at the start of this millennium exceeded 2.5 million tons per year. A growing worldwide concern for these problems has motivated researchers, administrators, and farmers to seek alternatives to chemical-based, conventional agriculture. One such product is effective microorganisms (EM) developed by Japanese scientists. Effective microorganisms are a mixed culture of beneficial and naturally occurring microorganisms, such as species of photosynthetic bacteria (Rhodopseudomonas palustris and Rhodobacter sphaeroides), lactobacilli (Lactobacillus plantarum, L. casei, and Streptococcus lactis), yeasts (Saccharomyces spp.), and Actinomycetes (Streptomyces spp.). These beneficial microorganisms improve crop growth and yield by increasing photosynthesis, producing bioactive substances such as hormones and enzymes, controlling soil diseases, and accelerating decomposition of lignin materials in the soil. Experiments conducted on various agricultural crops in different parts of the world have shown good prospects for the practical application of these beneficial microorganisms in improving crop yield and soil fertility. Application of beneficial microorganisms generally improves soil physical and chemical properties and favors the growth and efficiency of symbiotic microorganisms such as nitrogen fixing rhizobia and arbuscular mycorrhizal (AM) fungi. Nonetheless experiences of some researchers revealed that the effect of these microorganisms on crop growth and yield was usually not evident or even negative in the first test crop. However, this adverse effect can be overcome through repeated applications of these microorganisms. Research on these microorganisms has shown that crop yields tend to increase gradually as subsequent crops are grown. Foliar application of beneficial microorganisms avoids many of the biotic and abiotic factors and constraints of the soil environment, and thus increases the crop growth and yield significantly. Application of beneficial microorganisms also reduces seed bank of weeds in agricultural soils by enhancing the rate of weed seeds germination. There are reports of management of various fungal and bacterial pathogens as well as insect pests due to application of beneficial microorganisms. These microorganisms have shown a great promise in dairy wastewater treatment. They can reduce NH₃ concentration in poultry manure up to 70% possibly by transforming NH ⁺₄ to NO ⁻₃ . Research conducted so far concludes that benefits of beneficial microorganisms can be best exploited through their repeated applications for few years in combination with organic amendments and applying them as foliar spray. Integrated use of organic matter plus beneficial microorganisms with half mineral NPK can yield equivalent to that of full recommended NPK fertilizers dose. Beneficial microorganisms can also be used for wastewater treatment, pest and disease management, and to reduce the abiotic stresses on crop growth and yield.