This study was conducted to determine the suitable soil conditions for tomato cultivation under an organic farming system. Tomatoes were cultivated in chemically and organically fertilized experimental fields from 2013 to 2015 in Moriyama City, Shiga prefecture, Japan. Organically and chemically fertilized soils had different total carbon (TC) and total nitrogen (TN) contents, and different carbon-to-nitrogen ratios (C/N ratios). The tomato yields varied from 1290 to 5960 kg/0.1ha in the organically fertilized fields. The organic soil conditions for the highest tomato yield showed a TC content of ~33,000 mg/kg, TN content of ~1600 mg/kg, and a C/N ratio of ~21. The yield was reproducible in the organic fields under similar values of TC, TN, and C/N ratio in the soil. Significantly higher nitrogen and phosphorus circulation activities were observed in the high-yielding fields. Appropriate control of TC, TN, and C/N ratio is necessary for the enhancement of both microbial activity and tomato yield. Values of the important tomato quality parameters (lycopene, glutamic acid, and acid content) were also increased in the highyielding tomato fields. We therefore suggest that a suitable soil condition for improving both the yield and quality of tomatoes in an organic farming system is TC of 30,000 -36,000 mg/kg, TN of 1600 -1900 mg/kg, and a C/N ratio of 18 -21.

Improvement of phosphorus circulation in the soil is necessary to enhance phosphorus availability to plants. Phosphorus circulation activity is an index of soil’s ability to supply soluble phosphorus from organic phosphorus in the soil solution. To understand the relationship among phosphorus circulation activity; bacterial biomass; pH; and Fe, Al, and Ca concentrations (described as mineral concentration in this paper) in agricultural soil, 232 soil samples from various agricultural fields were collected and analyzed. A weak relationship between phosphorus circulation activity and bacterial biomass was observed in all soil samples (R2 = 0.25), and this relationship became significantly stronger at near-neutral pH (6.0–7.3; R2 = 0.67). No relationship between phosphorus circulation activity and bacterial biomass was observed at acidic (pH < 6.0) or alkaline (pH > 7.3) pH. A negative correlation between Fe and Al concentrations and phosphorus circulation activity was observed at acidic pH (R2 = 0.72 and 0.73, respectively), as well as for Ca at alkaline pH (R2 = 0.64). Therefore, bacterial biomass, pH, and mineral concentration should be considered together for activation of phosphorus circulation activity in the soil. A relationship model was proposed based on the effects of bacterial biomass and mineral concentration on phosphorus circulation activity. The suitable conditions of bacterial biomass, pH, and mineral concentration for phosphorus circulation activity could be estimated from the relationship model.

To characterize the long-chain cyclic alkane (c-alkane) degradation of bacteria in Rhodococcus, we analyzed the relationship between the alkane hydroxylase gene (alkB) and long-chain c-alkane degradation in 19 species. Eleven strains which were isolated from nature using long-chain c-alkane as a substrate were identified as R. erythropolis, and all were shown to carry the alkB [alkB R2 type]. This gene type was also carried by two other species, R. rhodochrous and R. baikonurensis. In total, 17 species of the genus Rhodococcus carried alkB, but the gene types differed from each other. The two species R. rhodnii and R. coprophilus did not carry alkB, and their long-chain c-alkane degradation levels were low.

Possibility of wood biomass for preparing organic soil was examined to construct reproducible and stable organic standard soil. Seven organic soils were constructed from base soils and additive materials based on the recommended values of the soil fertility index (SOFIX) (total carbon ≥ 25,000 mg/kg, total nitrogen ≥ 1500 mg/kg, total phosphorus ≥ 1100, and total potassium of 2500 to 10,000 mg/kg). Base soils were prepared from two types of wood biomass (big-and small-sized wood chips) at 50%, 60%, and 70% (v/v) and other organic materials such as peat moss, black soil, and mountain soil. Additive materials (soybean meal, oil cake, cow manure, and bone meal) were amended into all organic soils at the same amount. Incubation experiment showed that bacterial biomass in all organic soil was greater than 6 × 10 8 cells/g-soil after addition of 30% of water content for 1 week. In addition, polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analysis resulted in a stable bacterial diversity of the organic soil prepared from the small size wood chip at 70%. Chemical properties of all organic soils were within the recommended values of SOFIX. The plant cultivation experiment showed that fresh Brassica rapa var. peruviridis weights in the organic soils with 50%, 60%, and 70% of small-sized wood chip were 5%, 16%, and 27% higher than that of the chemical fertilizer-amended soil. The organic soil with 70% of small wood chip was the best in the seven organic soils in this study.

Possibility of wood biomass for preparing organic soil was examined to construct reproducible and stable organic standard soil. Seven organic soils were constructed from base soils and additive materials based on the recommended values of the soil fertility index (SOFIX) (total carbon ≥ 25,000 mg/kg, total nitrogen ≥ 1500 mg/kg, total phosphorus ≥ 1100, and total potassium of 2500 to 10,000 mg/kg). Base soils were prepared from two types of wood biomass (big-and small-sized wood chips) at 50%, 60%, and 70% (v/v) and other organic materials such as peat moss, black soil, and mountain soil. Additive materials (soybean meal, oil cake, cow manure, and bone meal) were amended into all organic soils at the same amount. Incubation experiment showed that bacterial biomass in all organic soil was greater than 6 × 10 8 cells/g-soil after addition of 30% of water content for 1 week. In addition, polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analysis resulted in a stable bacterial diversity of the organic soil prepared from the small size wood chip at 70%. Chemical properties of all organic soils were within the recommended values of SOFIX. The plant cultivation experiment showed that fresh Brassica rapa var. peruviridis weights in the organic soils with 50%, 60%, and 70% of small-sized wood chip were 5%, 16%, and 27% higher than that of the chemical fertilizer-amended soil. The organic soil with 70% of small wood chip was the best in the seven organic soils in this study.