Toshinori Nagaoka

Relative importance of protons and solution calcium concentration in phosphate rock dissolution by organic acids

Abstract A series of experiments was conducted to quantify the relative contribution of protons and other mechanisms to the dissolution of phosphate rocks (PRs) from six countries in solutions of low-molecular-weight-aliphatic organic acids. The amounts of P and Ca released after 3 d of incubation at 28°C were determined in all the experiments. In the first experiment the solubility of the PRs < 500 μm particle size) in 100 M (25 mL g-1 PR) oxalic, tartaric, and citric acids was compared with that in three mineral acids and four chelating compounds. There were no differences in the amount of P released by the mineral acids, but the organic acids released more P than could be accounted for by protonation. The chelating compounds were the least effective. In the second experiment, 1 g each of Sri Lanka and Togo PRs was incubated with 2.5 mmol of the organic acids using three acid concentration (mM) : acid volume ratios (250:10, 100:25, and 25:100). The amount of P dissolved from the PRs and the amount of ac...

Relationships between microbial biomass nitrogen, nitrate leaching and nitrogen uptake by corn in a compost and chemical fertilizer-amended regosol

Abstract To determine the relationships between microbial biomass nitrogen (N), nitrate–nitrogen leaching (NO3-N leaching) and N uptake by plants, a field experiment and a soil column experiment were conducted. In the field experiment, microbial biomass N, 0.5 mol L−1 K2SO4 extractable N (extractable N), NO3-N leaching and N uptake by corn were monitored in sawdust compost (SDC: 20 Mg ha−1 containing 158 kg N ha−1 of total N [approximately 50% is easily decomposable organic N]), chemical fertilizer (CF) and no fertilizer (NF) treatments from May 2000 to September 2002. In the soil column experiment, microbial biomass N, extractable N and NO3-N leaching were monitored in soil treated with SDC (20 Mg ha−1) + rice straw (RS) at five different application rates (0, 2.5, 5, 7.5 and 10 Mg ha−1 containing 0, 15, 29, 44 and 59 kg N ha−1) and in soil treated with CF in 2001. Nitrogen was applied as (NH4)2SO4 at rates of 220 kg N ha−1 for SDC and SDC + RS treatments and at a rate of 300 kg N ha−1 for the CF treatment in both experiments. In the field experiment, microbial biomass N in the SDC treatment increased to 147 kg N ha−1 at 7 days after treatment (DAT) and was maintained at 60–70 kg N ha−1 after 30 days. Conversely, microbial biomass N in the CF treatment did not increase significantly. Extractable N in the surface soil increased immediately after treatment, but was found at lower levels in the SDC treatment compared to the CF treatment until 7 DAT. A small amount of NO3-N leaching was observed until 21 DAT and increased markedly from 27 to 42 DAT in the SDC and CF treatments. Cumulative NO3-N leaching in the CF treatment was 146 kg N ha−1, which was equal to half of the applied N, but only 53 kg N ha−1 in the SDC treatment. In contrast, there was no significant difference between N uptake by corn in the SDC and CF treatments. In the soil column experiment, microbial biomass N in the SDC + RS treatment at 7 DAT increased with increased RS application. Conversely, extractable N at 7 DAT and cumulative NO3-N leaching until 42 DAT decreased with increased RS application. In both experiments, microbial biomass N was negatively correlated with extractable N at 7 DAT and cumulative NO3-N leaching until 42 DAT, and extractable N was positively correlated with cumulative NO3-N leaching. We concluded that microbial biomass N formation in the surface soil decreased extractable N and, consequently, contributed to decreasing NO3-N leaching without impacting negatively on N uptake by plants.

Isolation and Characterization of Cellulose-decomposing Bacteria Inhabiting Sawdust and Coffee Residue Composts

Clarifying the identity and enzymatic activities of microorganisms associated with the decomposition of organic materials is expected to contribute to the evaluation and improvement of composting processes. In this study, we examined the cellulolytic and hemicellulolytic abilities of bacteria isolated from sawdust compost (SDC) and coffee residue compost (CRC). Cellulolytic bacteria were isolated using Dubos mineral salt agar containing azurine cross-linked (AZCL) HE-cellulose. Bacterial identification was performed based on the sequence analysis of 16S rRNA genes, and cellulase, xylanase, β-glucanase, mannanase, and protease activities were characterized using insoluble AZCL-linked substrates. Eleven isolates were obtained from SDC and 10 isolates from CRC. DNA analysis indicated that the isolates from SDC and CRC belonged to the genera Streptomyces, Microbispora, and Paenibacillus, and the genera Streptomyces, Microbispora, and Cohnella, respectively. Microbispora was the most dominant genus in both compost types. All isolates, with the exception of two isolates lacking mannanase activity, showed cellulase, xylanase, β-glucanase, and mannanase activities. Based on enzyme activities expressed as the ratio of hydrolysis zone diameter to colony diameter, it was suggested that the species of Microbispora (SDCB8, SDCB9) and Paenibacillus (SDCB10, SDCB11) in SDC and Microbispora (CRCB2, CRCB6) and Cohnella (CRCB9, CRCB10) in CRC contribute to efficient cellulolytic and hemicellulolytic processes during composting.

Steroidal alkaloids from roots of tomato stock

Abstract Six new steroidal alkaloids were isolated from roots of a hybrid of Lycopersicon esculentum x L. hirsutum and their structures elucidated as 5α-tomatidan-3-one, (23 R )-23-acetoxytomatidine, (23 S )-23- acetoxysoladulcidine, (23 S ,25 S )-23-acetoxy-5α,22α N -spirosolan-3β-o1; 22,26-epimino- 16β,23-epoxy-23α-ethoxy-5α,25αH-cholest-22( N )-ene-3β,20α-diol and 22,26-epimino-16β, 23-epoxy-5α,22βH,25αH-cholestane-3β,23α-diol, respectively.

Antifungal Activity of Oosporein from an Antagonistic Fungus against Phytophthora infestans

An antifungal metabolite, oosporein, was isolated from the culture of Verticillium psalliotae that produced the antagonistic effects on Phytophthora infestans. Oosporein exhibited a significant growth-inhibitory effect on P. infestans in comparison with other phytopathogenic fungi.

Comparative physiological analysis of salinity tolerance in rice

Abstract Comparative physiological analysis was performed to understand the differences in the mechanisms of salinity tolerance in two rice (Oryza sativa L.) cultivars (the tolerant cultivar CFX18 and the susceptible cultivar Juma67). It was found that growth was significantly decreased in Juma67, but not in CFX18, during 10 d of salinity treatment. Under high salinity conditions, CFX18 maintained a better physiological status as determined by higher leaf water potential and a lower electrolyte leakage ratio compared to Juma67. Analysis of photosynthesis-intercellular carbon dioxide (CO2) concentration response curves revealed decreases in both carboxylation efficiency and maximum photosynthetic CO2 fixation rate in Juma67 in response to salinity stress, suggesting reduced photosynthetic capacity in this cultivar. In addition, it was observed that under high salinity conditions, Juma67 accumulated 3.5 times more sodium ions (Na+) in the leaves compared to CFX18. To corroborate this observation, quantitative expression analysis was conducted to examine changes in the transcript levels of OsHKT1;5, which is responsible for the regulation of Na+ accumulation in shoots. It was found that salinity stress repressed expression of the OsHKT1;5 gene in the leaves of Juma67, but not CFX18. These results suggest that CFX18 and Juma67 differ in their profiles of Na+ accumulation under salinity stress because of differences in OsHKT1;5 expression. Thus, the mechanism of salinity tolerance seen in CFX18 relies on regulating Na+ accumulation in leaves and this trait would be useful for improving salinity tolerance in rice.

Compost amendment enhances the biological properties of Andosols and improves phosphorus utilization from added rock phosphate

Abstract The aim of the present study was to investigate the relationship between the uptake of phosphorus (P) from rock phosphate (RP) by plants and the enhancement of the biological properties of the soil by compost amendments. In experiments conducted in Wagner’s pots (200 cm2), the enrichment of Andosols with RP at 0, 100, or 200 mg P kg−1 soil was combined with the addition of one of four types of compost at a rate equivalent to 13.3 mg P kg−1 soil or with no compost treatment, and the amended soils were used to grow African millet (Eleusine coracana Gaertn, cv. Yukijirushi) for 60 days. The composts added to the soil were based on poultry manure (PM), cattle manure (CM), sewage sludge (SS), or P-adjusted sawdust (PSD). In an incubation experiment, RP was added at 0 or 150 mg P kg−1 of soil in combination with each of the four types of compost at the same rate of application as in the pot experiment, or with no compost. The uptake of P from RP (RP-P) by plants was highest with PM, followed by CM and PSD, and then SS; it was four- to five-fold more with compost addition than no compost addition. Microbial biomass P was significantly higher when RP was added with PM or CM. RP-P uptake by plants showed a positive correlation (r = 0.72, P < 0.05) with the microbial biomass P in the soil. In the soil incubation, the population density of phosphate-solubilizing bacteria (PSB) was significantly higher in compost-amended soils than in the absence of compost treatment, and was highest with the addition of PM. The available P in soil showed a positive correlation (r = 0.70, P < 0.05) with the population density of PSB. These results show that the uptake of P from RP by plants is enhanced by amendment with compost, especially PM or CM compost, and is strongly related to the biological properties of the soil, such as the microbial biomass P and the population density of PSB.

Selective inhibitors of germination of legume seeds in activated sludge compost

Water extracts of the compost produced from activated sludge and coffee residue were found to be selectively inhibitory to seed germination of some legumes. Germination rate of white clover (Trifolium repens L.), red clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.) seeds were reduced to 2, 29 and 73% of the control, respectively, by water extracts of the compost (20 g l−1). However, the extracts did not show any inhibition to seed germination of sorghum (Sorghum bicolor Moench), African millet (Eleusine coracana Gaertn.), and Komatsuna (Brassica rapa L.) at the same concentration. The inhibitors in the compost extracts were separated by ion-exchange chromatography and reverse-phase high performance liquid chromatography (HPLC) and the inhibitory activities of seed germination were tested with white clover seeds. Five inhibitors were isolated and identified as 3,4-dichlorophenylacetic acid (3,4-DCP), 3,4-dichlorobenzoic acid (3,4-DCB), 3,4,5-trichlorophenylacetic acid, 3,4,5-trichlorobenzoic acid and mono-2-ethylhexylphthalate by 1H-, 13C-NMR spectroscopy and mass spectrometry. The inhibitory activities of some authentic chemicals of the inhibitors and the related compounds were compared. The results indicated that the main inhibitor in the compost could be 3,4-DCB, which was contained at the concentration of 6.58 mg kg−1 compost and showed the strongest inhibitory effect on seed germination of white clover among the tested compounds.

Sesquiterpenoids in Root Exudates of Solanum aethiopicum

Abstract Five known sesquiterpenoids, solavetivone, lubimin, lubiminoic acid, aethione and lubiminol were isolated from the root exudates recovered from Solanum aethiopicum by a newly proposed method using charcoal. Quantitative analysis of the sesquiterpenoids in the root exudates of S. aethiopicum and S. melongena suggested that relatively large amounts of the sesquiterpenoids were exuded from the roots. Antifungal activity of the sesquiterpenoids against Fusarium oxysporum and Verticillium dahliae was also examined.

Nitrate leaching in granitic regosol as affected by N uptake and transpiration by corn

Abstract Field and soil column experiments were conducted to analyze the effects of N uptake and transpiration by corn on nitrate–nitrogen (NO3-N) leaching in a granitic regosol and to evaluate the contribution of plant growth to the reduction of NO3-N leaching. In the field experiment, NO3-N leaching, N uptake by corn and retained N (inorganic N and microbial biomass N) were monitored in conventional planting density (CPD), high planting density (HPD) and no planting (NP) treatments. Nitrogen (N) was applied as (NH4)2SO4 at the rate of 300 kg N ha−1 and corn (Zea mays L.) was sown. In the soil column experiment, 1,500 mg N per column was applied and corn was sown in four treatments: no plants (NP), 1-plant, 2-plants and 4-plants per column. NO3-N leaching, N uptake and transpiration by corn and retained NO3-N in the soil were measured. In the field experiment, cumulative NO3-N leaching in the NP treatment was 208 kg N ha−1 from 38 to 49 days after treatment. In the CPD and HPD treatments, NO3-N leaching was reduced to 148 kg N ha−1 and 73 kg N ha−1, respectively. Nitrogen uptake by corn and retained N in the soil increased with increasing plant density. Cumulative NO3-N leaching was negatively correlated with N uptake by corn (r = −0.940, P < 0.01, n = 10). NO3-N leaching decreased as N uptake by corn increased above 60 kg N ha−1. In the soil column experiment, cumulative NO3-N leaching decreased with increased planting density because of increased N uptake by corn and the amount of retained NO3-N in the soil. The amount of retained NO3-N in the soil was positively correlated with transpiration by corn (r = 0.943, P < 0.01, n = 12). We concluded that NO3-N leaching from a granitic regosol during the rainy season could be reduced by increasing the planting density because of the increase in N uptake by plants and the increase of retained N in the soil derived from the increase in transpiration by plants.