Inorganic nitrogen movement in tropical soils

A field experiment was conducted to follow the transformation of ammonium fertilizer applied in rainfed-upland fields. The study was done during the rainy season on a heavy-textured, poorly rained soil. Ammonium fertilizer was applied in rows, and soil samples from different depths were analyzed to check the vertical distribution of inorganic nitrogen. In order to learn the relation between nitrogen loss and nitrification, the effect of nitrification inhibitor was also checked. Ice variety IR5 was used to check nitrogen uptake.

The ammonium content decreased by about 40 per cent up to I month after fertilizing and about 90% up to 2 months after fertilizing in the unplanted plots. Up to 5 months it decreased to a level equal to or lower than that before fertilizer application. The accumulation of nitrate was observed in the lower soil layers-after 3 months, but the accumulated amount was too low to account for the loss of ammonia from the surface. The overall loss of mineral nitrogen within 60 cm of the surface was observed after 5 months in unplanted plots. The addition of nitrification inhibitor retarded the decrease of ammonium nitrogen up to 2 months. After 3 months, the nitrifying activity began to recover.

Only 23 to 27 per cent of the fertilizer nitrogen was taken up by the rice plants, indicating low efficiency.     

Fate of Azolla spp. and urea nitrogen applied to wetland rice (Oryza sativa L.)

Summary Using ¹⁵N, the fate of N applied to wetland rice either as Azolla or urea was studied in a field at the International Rice Research Institute (IRRI). In bigger plots nearby, yield response and N uptake were also determined with unlabelled N sources. Azolla microphylla was labelled by repeated application of labelled ammonium sulfate. Labelled and unlabelled N were used alternately in applications of Azolla or urea 0 and 42 days after transplanting, in order to determine the effect of the time of application on the availability of Azolla N. The quantities of Azolla N incorporated were 23% more than those of urea N (30 kg N ha^–1) in the isotope plots or 7% less in the yield response plots. Grain yield and total N uptake by the rice plants in the yield-response plots were higher in the urea-treated plots than in the Azolla-treated plots, but the physiological effect of Azolla N (grain yield response/increase in N uptake) was higher than that of rea. The labelled N balance was studied after the first and second crops of rice. Losses of labelled N after the first crop were higher from urea (30%–32%) than from Azolla (0%–11 %). Losses in N applied as a side dressing 42 days after transplanting were less than those of N applied basally. No further losses of ¹⁵N occurred after the first crop. The recovery of Azolla ¹⁵N in the first crop of rice was 39% from the basal application and 63% from the side dressing. The recovery of urea ¹⁵N was 27% from the basal application and 48% from the side dressing. Recoveries of residual N from both Azolla and urea during the second rice crop were similar. Laboratory incubation of the Azolla used and the changes in labelled exchangeable N in the soil showed that at least 65% of Azolla N (4.7% N content) was mineralized within 10 days.     

Mechanisms of Aluminum Tolerance in Phosphoenolpyruvate Carboxylase Transgenic Rice

Transgenic rice, in which C4-phosphoenolpyruvate carboxylase (PEPC) is overexpressed, was grown in hydroponic culture to evaluate its tolerance for high aluminum (Al) content in relation to organic acid synthesis and exudation into the rhizosphere. With regard to root growth in short-term experiments, PEPC-transgenic rice was more tolerant of Al than the wild type. At increased Al levels in the root medium, root tips of the transgenic rice accumulated less Al than those of the wild type. Aluminum-induced oxalate exudation from roots occurred at increased rates in the transgenic line. Overexpression of C4-PEPC drastically increased PEPC activity in leaves of the transgenic rice, causing higher organic acid concentrations in leaves and roots. The increased organic acid concentrations seemed to cause higher exudation rates of oxalate from roots, leading to a detoxification of Al in the root apoplast and rhizosphere.     

Specific detection of potentially allergenic kiwifruit in foods using polymerase chain reaction

Kiwifruit (Actinidia deliciosa and Actinidia chinensis) is allergenic to sensitive patients, and, under Japanese regulations, it is one of the food items that are recommended to be declared on food labeling as much as possible. To develop PCR-based methods for the detection of trace amounts of kiwifruit in foods, two primer pairs targeting the ITS-1 region of the Actinidia spp. were designed using PCR simulation software. On the basis of the known distribution of a major kiwifruit allergen (actinidin) within the Actinidia spp., as well as of reports on clinical and immunological cross-reactivities, one of the primer pairs was designed to detect all Actinidia spp. and the other to detect commercially grown Actinidia spp. (i.e., kiwifruit, Actinidia arguta, and their interspecific hybrids) except for Actinidia polygama. The specificity of the developed methods using the designed primer pairs was verified by performing PCR experiments on 8 Actinidia spp. and 26 other plants including fruits. The methods were considered to be specific enough to yield target-size products only from the target Actinidia spp. and to detect no target-size products from nontarget species. The methods were sensitive enough to detect 5-50 fg of Actinidia spp. DNA spiked in 50 ng of salmon testis DNA used as a carrier (1-10 ppm of kiwifruit DNA) and 1700 ppm (w/w) of fresh kiwifruit puree spiked in a commercial plain yogurt (corresponding to ca. 10 ppm of kiwifruit protein). These methods would be expected to be useful in the detection of hidden kiwifruit and its related species in processed foods.     

Growth inhibition due to continuous cropping of dryland rice and other crops

Rice, corn, sorghum, mungbeans, and cowpeas were continuously grown on the same land at 2- to 6-week intervals between crops to determine effects on yield. Decline of growth and yield occurred during continuous cropping. Dryland rice, mungbeans, and cowpeas were affected most, corn slightly, and sorghum was not visibly affected.

Growth inhibition in dryland rice and mungbeans occurred after one or two crops; growing the same crop in rapid succession resulted il1low grain yields. The persistence of inhibitory effects was indicated. One crop rotation or 5 months of fallow removed only a part of the harmful effects.

The causal agent appears to have a specific affinity to the host crop. Root residues of the previous crop may serve as a source of the causal agent for the subsequent crop.

Biological agents were involved in growth inhibition of rnungbeans and dryland rice. In mungbeans, the inhibitory effects appeared to be directly dependent on microorganisms. It appeared that microorganisms were not the primary cause of harmful effects in dryland rice.     

Origin and properties of humus in the subsoil of irrigated rice paddies

Stability of humus in the plow layer soil is considered to affect the quantity and quality of dissolved organic matter leached from the plow layer soil. Therefore, a model experiment was conducted to analyze the effect of soil reduction under submerged conditions on the stability of humus in the plow layer soil. The changes in the stability of humus in the plow layer soil during submerged incubations with and without rice straw application were evaluated based on the changes in the binding type of humus. Binding type of humus in the plow layer soil was analyzed by successive extractions of organic matter with water, 0.25 M Na₂SO₄, 0.1 M Na₄P₂O₇ (pH 7.0), 0.1 M Na₄P₂O₇ (pH 10.5), and 0.1 M Na₄P₂O₇ (pH 10.5) with NaBH₄. Amounts of Fe, Mn, and Mg in each fraction were also determined to estimate the relationships between humus and metals.

The successive extraction of humus indicated that the amount of organic carbon which was extractable with the (NaBH₄ +0.1 M Na₄P₂O₇) solution decreased while that of the 0.1 M Na₄P₂O₇ (pH 7.0}-extractable organic carbon increased during submerged incubation with rice straw application. The origin of the increase in the amount of organic carbon in the Na₄P₂O₇ (pH 7.0)-extractable fraction during submerged incubation was investigated further by another incubation experiment using ¹³C-glucose as a reducing agent. Atom- 13C% analysis showed that the contribution of organic carbon derived from compounds other than glucose to the increase in the contents of humic acids and fulvic acids in the Na₄P₂O₇ (pH 7.0)-extractable fractions was ca. 80%. Therefore, it was concluded that the binding type of humus changed from (NaBH₄ + Na₄P₂O₇)-extractable to Na₄P₂O₇ (pH 7.0)-extractable humus under reducing conditions. Since the amounts of organic carbon and Fe increased in the Na₄P₂O₇ (pH 7.0)-extractable fraction and decreased in the (NaBH₄ +0.1 M Na₄P₂O₇)-extractable fraction simultaneously, iron reduction was presumably associated with the change in the binding type of humus in submerged paddy soil.     

Identification of a Germicidal Compound against Picornavirus in Bamboo Pyroligneous Acid

The germicidal activity of pyroligneous acid (PA) against a picornavirus, encephalomyocarditis virus (EMCV), was analyzed, and the component responsible for its disinfectant activity was identified. Bamboo PA (BPA) inactivated EMCV, but neutralization of BPA abolished this activity. Using liquid-liquid phase extraction and silica gel column chromatography, the hydrophobic active fraction of BPA was separated and its 12 major components were identified. The active fraction was reconstructed by mixing synthetic chemicals at the determined concentrations, and a subtraction series of one chemical from the complete mixture was prepared. An in vitro virus assay demonstrated that phenol was the sole germicidal component, and acetic acid augmented the phenol's inactivating activity resulting in >5-log decrease in EMCV infectivity. Considering the low environmental risk of PA, these findings suggest that BPA is a potentially useful agent for preventing viral epidemics in agricultural and human environments.     

Changes in allergenicity and digestibility of squid tropomyosin during the Maillard reaction with ribose

The effect of the Maillard reaction on the allergenicity of squid tropomyosin (TM) was investigated. When TM was reacted with ribose (TM-ribose), its human-specific IgE-binding ability decreased markedly and alpha-chymotryptic digestibility of TM was also altered at the early stage of the Maillard reaction. On the other hand, the modification of the lysine residues in TM using 2,4,6-trinitrobenzenesulfonic acid had no effect on the allergenicity and alpha-chymotryptic digestibility of TM. Therefore, the structural change in TM induced by the Maillard reaction would cause the reduction of the allergenicity, rather than the block of lysine residues. Although peptic digestion diminished the specific IgE-binding ability of TM, the reduction of the allergenicity by the Maillard reaction remained after peptic digestion. These results suggest that hypersensitive reaction of TM-ribose in the human body might be lower than that of native TM.     

Evaluation and validation of a commercially available enzyme-linked immunosorbent assay for the neonicotinoid insecticide imidacloprid in agricultural samples

The performance of a commercially available microtiter plate ELISA kit for the determination of the neonicotinoid insecticide imidacloprid was evaluated for sensitivity, selectivity, influence of organic solvent used for extraction procedure, matrix interference originated from agricultural sample, accuracy, and method comparison with conventional HPLC analysis. The limit of detection for the kit (0.1 or 0.5 ng/mL) was determined. The working range (1-39 ng/mL) experimentally calculated on the basis of a criterion, which is determined as the range from I(20) to I(80), was comparable to that established by the manufacturer (1-50 ng/mL). The linearity of the standard curve based on the kit-assembled standard solutions agreed with the one based on the self-made standard solutions. Specificity studies indicate that the imidacloprid monoclonal antibody can readily distinguish the target compound from other structurally related neonicotinoid analogues and some metabolites, with the exception of clothianidin, the cross-reactivity of which was approximately 12%. To extract imidacloprid from an agricultural sample (apple) as simply and rapidly as possible, some extraction methods were examined. Consequently, the extraction method with hand-shaking for 5 min was the best among the examined methods. For the analysis of imidacloprid in apple samples, it was extracted directly with methanol and the extracts were diluted 10-fold (100-fold in the well) with water prior to ELISA analysis. No significant matrix interference was observed with the dilution factor. Recoveries of imidacloprid from fortified apple samples ranged from 87.7 to 112.0%. The results obtained with the ELISA kit correlated well with those by the reference method (conventional HPLC analysis) for apple samples (r > 0.998). These findings strongly indicate that the ELISA kit may be employed routinely for an on-site imidacloprid residue analysis of apple samples.