Improving soil environment by controlling the organic matter level and nutrient ratio in the soil is important for soil micro organisms.In our previous study, we developed a soil fertility index, SOFIX, for the evaluation of soil fertility . Analysis of the SOFIX data from several agricultural fields clearly showed that the number and activities of microorganisms can be significantly enhanced by controlling total carbon and total nitrogen contents, and carbon-to-nitrogen ratios at ≥25,000 mg/kg, ≥2500mg/kg, and 10 – 25, respectively. However, the relationship between microbial activities and plant growth remains unknown. The objective of this study was to determine suitable soil conditions for improving the yield and quality of to matounder an organic farming system by enhancing the number and activities of soil microorganisms. Tomatoes were harvested once the fruits turned light red.
In all years, harvesting began at the end of June and lasted until the beginning of August. On the last day, all remaining fruits were also picked for weighing. The quality of tomato was also analyzed in the three organic fields in 2015 and compared with the yield . Lycopene and glutamicacid contents in Fields H and I were significantly higher than those in Field H . In contrast,no significant differences in antioxidant content, polygalacturonase activity,and sugar content were observed among the three fields, but the acid content in Field G was slightly lower than in Field I. Therefore, the soil conditions of Fields H and I would improve both yield and quality in tomato cultivation.Bacterial biomass and nutrient circulation activities were examined in the three organic fields of 2015 . The bacterial biomass in the fields ranged from 9.0 × 108 to 1.4 × 109 cells/g-soil. No relationship between bacterial biomass and tomato yield was observed, but the N and P circulation activities were significantly higher in Fields H and It han those in Field G.
The results suggest that high levels of N and P circulation activities in soil contributes for the enhancement of tomato yield and quality. Recent reports show that only 1% of agricultural fields in the world are cultivated under an organic farming system . This is typically because the yields under organic farming are unstable or because a successful organic cultivation requires several years of experience. In the current study, we investigated the suitable soil conditions for tomato cultivation under an organic farming system.Soil microorganisms play several beneficial roles in cultivated land such as decomposition of organic materials, nitrification, and P mineralization. Therefore,microorganisms are important parameters for soil fertility. In our previous study, we showed that TC, TN, and C/N ratio are closely related to the bacterial biomass and nutrient cycling activities in soil Enhancement of microorganisms and their activities are more important under organic systems than under conventional systems, because microorganisms help to supply nutrients to plants by decomposing the added organic materials. Properly controlled TC, TN and C/N ratios result in a high level bacterial biomass and enhanced N and Pcirculation activities.
Generally, the yields under organic systems are either unstable or lower compared to those in the conventional systems. Nitrogen availability is the most important in limiting yield of tomato under organic farming systems . A previous study demonstrated that high level of tomato yields under organic farming systems than that under conventional systems was associated to the high nitrogen mineralization rate and higher microbial diversity in soils under organic systems.In this study, we found that properly controlled TC, TN, and C/N ratio and high levels of N circulation activity and P circulation activity resulted into higher tomato yield in the organic fields compared to the chemically fertilized fields. Therefore, enhancement of the number and activities of microorganisms by maintenance of the soil condition seem necessary for achieving high yield of tomato from organic farming systems.Organic crop products are typically considered to be of high quality.In general, quality and quantity are oppositely related in crop products obtained under conventional farming systems . In this study, lycopene, glutamic acid,and acid contents in tomato fruit seemed to be enhanced in the high-yielding organic fields. Lycopene is a major antioxidant component , and glutamic acid, sugar, and acidity are the major taste indicators in tomato . Enhancement of sugar and organic acid contents in organically produced tomatoes have also been reported previously . Therefore, appropriate soil conditions in organic systems not only enhance the yield of tomato but also can improve the quality.A suitable organic soil condition of tomato would be also effective for other vegetable fruits. In this point, the amount of TN and the balance of C/N in soil are most important, because higher C/N ratio inhibits reproduction and enhances vegetative growth . However, crop production could be increased only after the organic soil enhances activities of microorganisms maintaining appropriate nutrients for plants.