Hideaki Kai

Factors affecting immobilization and release of nitrogen in soil and chemical characteristics of the nitrogen newly immobilized: I. Effect of Temperature on Immobilization and Release of Nitrogen in Soil

Abstract Usually, immobilization and release of nitrogen in soil are going on continuously and concurrently, whereby the nitrogen of the decomposing system is transformed steadily from inorganic to organic state by immobilization and back from organic to inorganic state by decay and mineralization. The driving agents of this turnover are soil microorganisms, C/N ratio, temperature, moisture, pH etc., and the energy needed to keep this cycle running derives from decomposable organic compounds added to soil in the forms of plant residues and excretions of roots and stored in the form of soil organic matter.

Drying effect on mineralizations of microbial cells and their cell walls in soil and contribution of microbial cell walls as a source of decomposable soil organic matter due to drying

Abstract 1) The mineralization of several kinds of microbial cells added to soil were accelerated considerably by the drying effect. 2) When microbial cells were roughly divided by mechanical procedure into two parts, i.e., cytoplasmic and cell wall substances, and separately added to soil with or without drying previously, the former was mineralized very quickly both with and without drying previously and its mineralization was not accelerated by the drying effect. The latter without drying previously was mineralized rather slowly, and the latter with drying previously was mineralized very quickly and remarkably. Furthermore, the former with and without drying previously left hardly any residual matter in soil, but the latter without drying previously left considerable residual matter because of making a complex resistant to microbial decomposition with colloid materials such as clay minerals and humus, and mineralization of the residual matter was remarkably accelerated by the drying effect. 3) From the...

Factors affecting immobilization and release of nitrogen in soil and chemical characteristics of the nitrogen newly immobilized III. Transformation of the nitrogen immobilized in soil and its chemical characteristics

Abstract The immobilization and release process of nitrogen and the chemical characteristics of newly immobilized-, subsequently released-, and residual-N were studied in soils receiving KNO3 labelled with 15N together with glucose, straw, and cellulose. Immobilization of nitrogen proceeded rapidly and reached its maximum at incubation periods of 3 days to 8 weeks or more, varying with the kind of carbon sources added. Following the maximum tie-up of nitrogen a rapid release began. After 20 weeks the immobilized nitrogen was released at a considerable rate for each carbon source. At the period of maximum immobilization of nitrogen added to soil there was a clear difference in the percentage distribution of various forms of organic nitrogen between applied-N and native-N. The former was higher in amino acid N and unidentified N and lower in nonhydrolyzable N than the latter, and almost the same in hexosamine N and ammonium N as the latter. With regard to all carbon sources the principal form of organic nit...

Factors affecting immobilization and release of nitrogen in soil and chemical characteristics of the nitrogen newly immobilized IV. Chemical nature of the organic nitrogen becoming decomposable due to the drying of soil

Abstract This study deals with the effect of air-drying or oven-drying a soil and remoistening it on the flush of decomposition of soil organic nitrogen and with a comparison of the chemical nature of the nitrogen mineralized between the newly immobilized nitrogen in a soil receiving glucose and KNO3 labelled with 15N and the native organic nitrogen in the soil. Mineralization of soil organic nitrogen was remarkably accelerated through the effects of both air-drying and oven-drying, and the effect was much greater in the latter than in the former. The immobilized-N was made much more susceptible to mineralization than the native-organic N through the effect of air-drying or oven drying. In the course of mineralization of the native-organic N, air-drying enhanced the decrease of amino acid N, in particular after 6-weeks incubation. Also, oven-drying intensified the decrease of all the forms of N for the same incubation periods; the decrease was most remarkable in the forms of amino acid N, unidentified N, ...

Antimicrobial activity of bark-compost extracts

Abstract The application of bark-compost to farmland has been reported to suppress soil-borne diseases, including Fusarium wilt. The “bacterial type” microflora of the compost has been considered to play the significant role in disease control. Using the disk-diffusion technique, we found that acetone extracts of the bark-compost possessed strong antifungal activity against Fusarium oxysporum f. sp. cucumerinum . The extracts were relatively stable against heat treatment at 100°C and the antifungal extracts were also active against Gibberella zeae. Helminthosporium sigmoideum and Glomerella cingulata , fungi of interest to plant pathologists, but they were inactive against yeasts and procaryotic organisms. There might be a parallel between this selective antimicrobial activity of the acetone extracts of the bark-compost and the formation of the “bacterial type” microflora of the compost. Furthermore, we partially purified the acetone extracts by reverse-phase HPLC and found at least 10 active antifungal peaks in the chromatogram. These antifungal agents appear to be relatively low polar lipids.

Studies on the environmental conditions controlling nitrification in soil: I. Effects of ammonium and total salts in media on the rate of nitrification

Abstract It is well known that the loss of nitrogen from the cultivated field principally occurs in the following two ways: (a) denitrification of nitrate, (b) leaching down of nitrate by percolating water. The problem of nitrification in soil is very important in connection with the efficient use of nitrogenous fertilizers applied to both the paddy- and the upland-field.

Relationship between an accumulation of soil organic matter becoming decomposable due to drying of soil and microbial cells

Abstract The purpose of this experiment is to make clear the relationship between an accumulation of soil organic matter becoming decomposable due to drying of soil and microbial cells. The results are summarized as follows: 1) The accumulation of soil organic matter becoming decomposable due to drying occurred in the decomposition process of organic matter applied to soil, and its quantity clearly increased with an increase of microbial cells. Further, the accumulation increased in company with an increase ofreimmobilization during the decomposition process of organic matter applied to soil. 2) The accumulation of the decomposable soil organic matter was clearly recognized during the decomposition process of microbial cells in soil. The accumulation rate was higher in newly immobilized organic matter of Boil than in native soil organic matter. 3) It was suggested that microbial cells and their cell walls considerably contribute as a source of the decomposable soil organic matter.

Chemical fractions of organic nitrogen in acid hydrolysates given from microbial cells and their cell wall substances and characterization of decomposable soil organic nitrogen due to drying

Abstract 1) The major part of organic nitrogen fractions in acid hydrolysate which is mineralized through the decomposition process of cells of B. subtilis in sand for 2 weeks was the form of amino acid N, but the form of amino sugar N was hardly mineralized. Their cytoplasmic substances were mineralized quickly, but their cell wall substances comparatively slowly. When the latter, however, was pretreated with ultrasonic or oven-drying treatment, their mineralization was accelerated. The mineralization rate of the form of amino sugar N was remarkably high. 2) The major part of the decomposable organic nitrogen fractions due to the ultrasonicating or oven-drying effects in acid hydrolysates given from microbial cells and their cell wall substances was the forms of amino acid N and amino sugar N. The accelerating effect of oven-drying pretreatment on the mineralization of the form of amino sugar N was larger than that of ultras on icating pretreatment under this experimental conditions. 3) The amino acid co...

Growth inhibition of soil-borne pathogenic fungi by typical sterols

Abstract The application of bark-compost to farm land has been reported to suppress soil-borne diseases, including Fusarium wilts. The “bacterial type” microflora of the compost, that includes many antagonists, has been considered to play the major role in suppression of soil-borne plant pathogens. To elucidate the suppressive effect of hemlock bark-compost on soil-borne pathogenic fungi, one of the antifungal agents in bark-compost was isolated by preparative HPLC. From 2D-nuclear magnetic resonance spectra and high resolution mass spectrometry, the antifungal agent was determined to be 24R-ethylcholest-5-en-3β-ol (silosterol). Sitosterol is a normal secondary plant metabolite found throughout the plant kingdom. Furthermore, using reverse-phase HPLC, we found considerable amounts of cholesterol, campesterol and stigmasterol in acetone extracts of the bark-compost. These typical sterols had strong in vitro antifungal activity against Fusarium oxysporum f. sp. cucumerinum . We investigated the antimicrobial spectrum of cholesterol. It was active against Cochliobolus miyabeanus, Gibberella zeae, Glomerella cingulata, Alternaria alternata and Rhizoctonia solani , fungi of interest to plant and human pathologists. It was inactive against yeasts and procaryotic organisms, based on a disk-diffusion technique. We propose that there might be a parallel between this selective antimicrobial activity of the sterol and the formation of a “bacterial type” microflora of the compost. These findings suggest that the typical sterols, such as cholesterol, may function as defensive substances against pathogenic fungi at the external surface of higher eucaryotes, including the cuticle of higher plants and in kelatinized squames of the mammalian epidermis.

Changes in soil microbial flora after sodium chloride application with or without ammonium sulfate addition

Abstract The effect of the addition of NaCl at various concentrations or of a mixture of NaCI and (NH4)2SO4 to non-saline sandy loam soil in Thailand, and the changes in both number and kinds of soil microorganisms were examined periodically. The number of fungi increased with the increase of the NaCl concentration when NaCl was solely added to the soil and Penicillium sp. were dominant in the fungal flora. In contrast, the numbers of bacteria and actinomycetes decreased by the addition of NaCl. The combined addition of NaCl and (NH4)2SO4 decreased the number of fungi, although fungal population became more complex. In contrast, (NH4)2SO4 application to the NaCl-treated soils did not show an additional effect on the number of bacteria.