Approximately 1 trillion of microorganisms of 1,000-10,000 different species inhabit in 1g of soil. They serve an important role in cycle of material of carbon, nitrogen and phosphorus. Also soil microorganisms produce beneficial materials such as antibiotics and enzyme, which human race has applied to food and medicinal industry to ameliorate the quality of life. Microorganisms in the soil inhabit in the bodies of animals or insects in the form of symbiosis or in rhizosphere in the form of community and function as a crucial medium that impact intensely to the health of ecosystem.
Contemporary agriculture is intensive agriculture which demands relatively high labor force and capital for the size farmland. The extensive use of chemical pesticides and manure seriously harms the ecosystem of the soil. Therefore, the interest in eco-friendly agriculture such as microbial agent or crop rotation is getting higher and the endeavor to achieve sustainable agriculture is not only domestic but global. This study intends to restrain excessive usage of chemical pesticides and the health of eco-friendly agriculture by comparing the effects of eco-friendly agriculture and chemical pesticides on the ecosystem of soil microorganism, using various methods such as metagenomics, DGGE and phospholipid fatty acid analysis.
The result of pyrosequencing analysis using metagenome extracted from the red-pepper field showed that the community composition of phylum, the highest level of the bacterial classification system, stayed without a big change in a identical phylum form for 3 years. Also, gram negative bacteria such as Acidobacteria, Proteobacteria phylum takes up at least 60% in the whole community. Such result also was verified from the rate of gram negative bacteria and gram positive bacteria which is possibly from relatively abundance of carbon source. In addition, the proportion of β-proteobacteria, that participate in the existence of soil organism in the red-pepper field using eco-friendly agriculture, was found high which was verified as the identical with the result of measurement of soil organic matter. On the other hands, toward the lower level of the classification, differences between the treatment appeared and the number of unclassified bacteria increased. Within species level, the lowest level in the classification, over 90% of the bacteria was not classified, most of them unculturable. Species richness, which represents the diversity of soil bacteria, was found the highest in the red-pepper field with consortium microbial agent and crop rotation applied, lowest in the red-pepper field with agrochemical and crop continuation applied. Such result shows that application of eco-friendly agriculture has positive effect on the soil ecosystem while the prolonged use of chemical pesticide may harm the community composition of soil microorganism.
Moreover, the measurement of cultivation method and enzyme activities of soil and phospholipid fatty acid analysis for evaluation of the soil health implied that the red-pepper field with both consortium microbial agent and crop rotation showed most vitalized microorganism whereas the red-pepper field with agrochemical and crop continuation showed less vigorous movement and density. Also, crop continuation and using of chemical pesticides boosted the density of pathogenic microorganism, Pseudomonas oryhilabitans, P. brassicacearum in particular, as sighted from analyzing density of major bacteria from the result of pyrosequencing analysis. Analysis of fungal community by using DGGE, also confirmed existence of strain of Rhizoctonia solani AG-1 (IB) which causes Damping-off. These phenomenon could be the consequence of agrochemical and crop continuation that causes aggravation of soil health and destruction of ecosystem.
The analysis on soil microorganism community with various method confirmed that application of agrochemical and crop continuation has a negative impact on the ecosystem of soil whereas eco-friendly agriculture improved the density and vitality of microorganism in the red-pepper field. The cropping sysytem and the kind of agent influences the growth of red-pepper, quality and quantity of the fruit, all of them resulting higher under eco-friendly agriculture than agrochemical. Such result proves that the density and vitality of soil microorganism have direct influence on the crops and that the worse soil health may decrease the growth or quantity of the crop.
This case study verifies the positive impact on the growth of crop of eco-friendly agriculture that boosts vitality of microorganism and the negative impact on soil health of agrochemical and crop continuation of identical crop. The result of this study can be the fundamental data on the soil ecosystem and the impact on the crop especially today when eco-friendly agriculture is popularizing.