Junta Yanai

Does cadmium play a physiological role in the hyperaccumulator Thlaspi caerulescens

The southern French (Ganges) ecotype of Thlaspi caerulescens J & C Presl is able to hyperaccumulate several thousand mg Cd kg(-1) shoot dry weight without suffering from phytotoxicity. We investigated the effect of Cd on growth and the activity of carbonic anhydrase (CA), a typical Zn-requiring enzyme, of T. caerulescens in soil and hydroponic experiments. In one of the hydroponic experiments, T. caerulescens was compared to the non-accumulator Thlaspi ferganense N. Busch. In the soil experiment, additions of Cd at 5-500 mg kg(-1) soil increased the growth of T. caerulescens significantly. In the hydroponic experiments, exposure to Cd at 1-50 microM for three weeks had no significant effect on the growth of T. caerulescens, but decreased the growth of T. ferganense markedly even at the lowest concentration of Cd (1muM). Cadmium exposure significantly increased the CA activity in T. caerulescens, but decreased it in T. ferganense. The CA activity in T. caerulescens correlated positively with the Cd concentration in the shoots up to 6000 mg kg(-1), even though shoot Zn concentration was decreased by the Cd treatments. For comparison, Cd treatments had no consistent effect on the activity of superoxide dismutase in T. caerulescens. The results suggest that Cd may play a physiological role in the Cd-hyperaccumulating ecotype of T. caerulescens by enhancing the activities of some enzymes such as CA. Further research is needed to establish whether a Cd-requiring CA exists in T. caerulescens.

Geostatistical analysis of soil chemical properties and rice yield in a paddy field and application to the analysis of yield-determining factors

Abstract To obtain basic information for rational site-specific soil management for rice production, spatial variability of soil chemical properties and grain yield of rice was evaluated in a 50 m × 100 m paddy field. One hundred surface soil samples were collected from each of the 5 m × 10 m plots before puddling to investigate the spatial variability of their chemical properties: pH, EC, total C content, total N content, C/N ratio, contents of mineralizable N, inorganic N, available P, exchangeable Ca, Mg, K, and Na. Grain yield was also measured at harvest for the corresponding 100 plots. Geostatistical analysis was carried out to examine their within-field spatial variability using semivariograms, and multivariate analysis was also carried out to evaluate yield-determining factors. Geostatistical analysis of the soil properties indicated a high to moderate spatial dependence for all the properties except for the inorganic N content. The ranges of spatial dependence were about 20–30 m for the pH, EC, total C content, total N content, content of exchangeable Na, about 40 m for the contents of available P, mineralizable N, exchangeable Ca and Mg, and about 50–60 m for the C/N ratio and content of exchangeable K. Grain yield showed a moderate spatial dependence with a range of about 50 m. The results of spatial dependence enabled to prepare kriged maps of the soil properties and yield to compare their spatial distribution in the field. Multivariate analysis further showed, in combination with geostatistics, that the soil chemical properties contributed significantly to the yield as yield-determining factors and explained as much as 65% of the spatially structured or non-random variation of the yield. In conclusion, the possible benefit of site-specific soil management or precision agriculture was demonstrated even in an almost flat paddy field.

Radiocesium sorption in relation to clay mineralogy of paddy soils in Fukushima, Japan.

Relationships between Radiocesium Interception Potential (RIP) and mineralogical characteristics of the clay fraction isolated from 97 paddy soils (Hama-dori, n = 25; Naka-dori, n = 36; Aizu, n = 36) in Fukushima Prefecture, Japan were investigated to clarify the mineralogical factors controlling the (137)Cs retention ability of soils (half-life 30.1 y). Of all the fission products released by the Fukushima accident, (137)Cs is the most important long-term contributor to the environmental contamination. The RIP, a quantitative index of the (137)Cs retention ability, was determined for the soil clays. The composition of clay minerals in the soil clays was estimated from peak areas obtained using X-ray diffraction (XRD) analyses. The predominant clay mineral was smectite in soils from Hama-dori and Aizu, while this was variable for those from Naka-dori. Native K content of the soil clays was found to be an indicator of the amount of micaceous minerals. The average RIP for the 97 soil clays was 7.8 mol kg(-1), and ranged from 2.4 mol kg(-1) to 19.4 mol kg(-1). The RIP was significantly and positively correlated with native K content for each of the geographical regions, Hama-dori (r = 0.76, p < 0.001), Naka-dori (r = 0.43, p < 0.05), and Aizu (r = 0.76, P < 0.001), while it was not related to the relative abundance of smectite. The linear relationship between RIP and native K content not only indicate a large contribution of micaceous minerals to the (137)Cs retention ability of the soil clays, but also could be used to predict the (137)Cs retention ability of soil clays for other paddy fields in Fukushima and other areas.

Spatial variability of soil chemical properties in a paddy field.

Abstract To obtain basic information for site-specific soil management to improve nutrient use efficiency by plants, spatial variability of soil properties was evaluated in a 50 m × 100 m paddy field. Ninety-one surface soil samples were collected after harvest to investigate the spatial variability of their chemical properties: pH, EC, total C content, total N content, C/N ratio, contents of available P, exchangeable Ca, Mg, K, and Na. Fifty samples were also collected after transplanting to investigate that of nitrogen-related properties: total C content, total N content, C/N ratio, and contents of mineralizable N and inorganic N. Geostatistical analysis was carried out to examine within-field spatial variability using semivariograms and kriged maps as well as descriptive statistics. Descriptive statistics showed that the coefficient of variation for the EC, total C content, total N content, contents of available P, exchangeable K, Na, mineralizable N, and inorganic N exceeded 10%, suggesting a relatively high variability. Geostatistical analysis indicated a high spatial dependence for all the properties except for the pH and inorganic N content. The ranges of spatial dependence were about 20 m for EC, total C content, total N content, C/N ratio, contents of exchangeable Ca, Mg, Na, and mineralizable N, and about 40–50 m for the contents of available P and exchangeable K. Based on the results of spatial dependence, kriged maps were prepared for the properties to analyze their spatial distribution in the field. The results reflected the history of soil management of the field in addition to the characteristics of the inherent soil properties. In conclusion, rational sampling interval was evaluated at 20–50 m depending on the soil properties, and the need for site-specific soil management and possibility of precision agriculture were demonstrated even in an almost flat paddy field.

Effects of inorganic nitrogen application on the dynamics of the soil solution composition in the root zone of maize

The effect of inorganic nitrogen (N) fertilizer on the ionic composition of the soil solution under maize (Zea mays L.) was studied. A pot experiment was carried out with two treatments combined factorially, with or without N application (Ca(NO3)2; +N and −N treatments, respectively), and with or without plants. Three looped hollow fiber samplers were installed in each pot to sample soil solutions nondestructively from the root zone, seven times during the 50-day growth period. Plants were harvested on the 50th day, and their nutrient contents determined.Effects of N fertilizer on the soil solutions were observed by the first sampling, 2 days after sowing. The concentrations of Ca and NO3− and electrical conductivity (EC) increased significantly in the +N treatments as direct effects of fertilizer application. In addition, the concentrations of Mg, K, Na and H+ also increased and that of P decreased significantly as indirect effects caused by the re-establishment of chemical equilibria. This suggested the greater supply as well as the greater possibility of leaching loss not only of NO3− but also of Ca, Mg and K. In the treatments with plants, the concentrations of NO3−, Ca, Mg and K decreased with time and pH increased significantly compared with the unplanted soil. The depletion of N in the soil solution roughly agreed with the amount of N taken up by the plant. The depletions of K from the soil solution amounted to less than 10% of the amount of the K taken up, suggesting intensive replenishment of K from exchange sites in the soil. Depletions of Ca and Mg were several times higher than the amounts taken up, indicating that the depletions resulted from the adsorption of the divalent cations by the soil rather than uptake by plants. Because NO3− is hardly absorbed by exchange sites in soil and was the dominant anion in solution, it was concluded that NO3− had a major role in controlling cation concentrations in the soil solution and, consequently, on their availability for uptake by plants as well as their possible leaching loss. ei]H Marschner

Use of a looped hollow fiber sampler as a deyice for nondestructive soil solution sampling from the heterogeneous root zone

Abstract Information on the water and nutrient dynamics in the root zone is essential for appropriate soil management and fertilizer application, since the root zone is the area where soil and plant interact. It is especially important to study the dynamics of the soil solution composition and concentration because many previous studies on the mineral nutrition of plants grown in soil suggested that plant roots take up nutrients from the soil solution. It is, therefore, necessary to develop an appropriate apparatus for the collection of soil solutions from the heterogeneous root zone.

Spatial Variability of Organic Matter Dynamics in the Semi-Arid Croplands of Northern Kazakhstan

Chernozem soils have been recognized as one of the most important soils for food production and for the sink of organic matter on a global scale. Soil degradation or accelerated organic matter decomposition has been reported recently in northern Kazakhstan due to specific agricultural management such as summer fallow to increase the soil moisture for the cropping season. The objectives of the present study were 1) to evaluate the carbon-related properties of soil and plant in relation to the topography and amount of available water in upland fields, 2) to analyze their spatial variability using geostatistics and 3) to propose a rational system of management for the promotion of sustainable agriculture in this region. Field investigations were carried out in large-scale upland fields in Shortandy, northern Kazakhstan, where a crop rotation system had been developed on Typic Haplus-tolls or Southern Chernozem soils. The study field (14 km × 5 km) was divided into 70 plots (1 km × 1 km each) and, at the center of each plot, organic carbon (C) content (0–90 cm) and potentially mineralizable C content (0–15 cm) in soil, total, ear and shoot C contents in plant, and crop yield were investigated in addition to the elevation and soil water content at the beginning of the growing season. The total amount of C stored in soil (0–90 cm) was 170.9 t ha−1 with the highest C content of 39.8t ha−1 being recorded in the surface soil (0–15 cm). Potentially mineralizable C in soil (0–15 cm) amounted to 2.72 t ha−1, equivalent to 6.8% of the total C in the surface soil, suggesting that a considerable part of C in soil could be released as CO2 under favourable conditions for organic matter decomposition. Plant aboveground biomass C amounted to 1.8 t ha−1, of which 1.2 t ha−1 was returned to the field as plant residues and 0.6 t ha−1 was removed as crop (ear). Coefficients of variation in the amount of soil mineralizable C and plant properties exceeded 40%, suggesting a considerable variation in the field. Correlation analysis indicated that the elevation showed a positive relationship with the water content, soil organic C content (p < 0.01), content of potentially mineralizable C and plant yield (p < 0.05). The spatial patterns of the measured properties in the isarithmic maps showed that the content of soil organic C was the highest in the top plateau; water content, plant C content and yield were the highest in the north-facing slope area; whereas the values of all of these parameters were relatively low in the south-facing slope area. These results strongly suggest that the organic matter dynamics in the field was considerably affected by the topography and that the most favourable area for the storage of organic matter was different from that for food production. In conclusion, site-specific agricultural management based on the spatial patterns of organic matter dynamics would be a suitable option for harmonizing sustainable agricultural production with environmental conservation by reducing organic matter decomposition.

Determination of soil-related factors controlling initial mangrove (Rhizophora apiculata BL.) growth in an abandoned shrimp pond

Abstract To elucidate factors contributing to plant growth in a mangrove plantation, the height of mangrove trees (Rhizophora apiculata BL.) was measured in addition to relative ground level and soil properties in an abandoned shrimp pond in Thailand. Tree height was measured at 1,853 points in the 25 ha experimental site. Soil was sampled from 74 points and physical (hardness, water content) and chemical (e.g. total C and N) properties were determined. The mean tree height of 58.3 cm was relatively small for 2-year-old trees, and varied considerably with a coefficient of variation of 32.4%. The relatively low total C content of the soil, 0.68 × 10−2 kg kg−1, indicated a decline in organic matter content during the conversion from mangrove into shrimp pond. The negative correlation of tree height with relative ground level (P < 0.01) suggested that better growth was observed at a lower area. The important role of soil properties in determining tree height was demonstrated. By combining geostatistics with multivariate analysis, as much as 90% of the spatially structured or non-random variation of tree height was explained by taking into account soil properties in addition to topography. Together, the results suggest that site-specific management, such as site-specific organic matter application, is a feasible and effective option for mangrove rehabilitation.

Evaluation of soil nitrogen status in japanese agricultural lands with reference to land use and soil types

Abstract The nitrogen content of agricultural soils collected from throughout Japan was characterized according to the form and availability, and with reference to land use and soil types. In total, 147 plow layer soil samples were collected—80 from paddy fields and 67 from upland fields to include various soil types. Soil N was separated into four fractions: inorganic extractable-N (Iex-N), fixed NH4 +-N (Ifix-N), organic mineralizable-N (Omin-N), and organic stable-N (Osta-N). In the analysis, the total-N content was determined by the dry combustion method. The lex-N content was determined by extraction with a 2 mol L-1 KCI solution and the lfix-N content by extraction with a HF-HCI solution after removal of organic-No The Omin-N content was evaluated as the potentially mineralizable N based on a long-term incubation method and the Osta-N content was calculated as the difference between the contents of total-N and the above-mentioned three fractions. The average total-N content was 2,593 mg kg-1, of which the contents of lex-N, lfix-N, Omin-N, and OstaN were 37, 124, 159, and 2,273 mg kg-1, respectively. Thus the available fraction (Iex-N and Omin-N) accounted for 7.6%, and the stable fraction (Ifix-N and Osta-N) for 92.4% of totalN on the average. Assuming that the plow layer depth was 15 cm and the bulk density was 1.0 Mg m-3 , the amounts of total-N, lex-N, lfix-N, Omin-N, and Osta-N were 3,890, 56, 186, 239, and 3,411 kg ha-1 , respectively. The amount of the available fraction (295 kg ha-1) was comparable to the total annual N input (266 kg ha-1), whereas the amount of the stable fraction (3,597 kg ha-1) was more than ten times larger. In relation to land use, the lex-N content was lower (both absolute and relative contents) in paddy soils (32 mg kg-1, 1.4%) than in upland soils (43 mg kg-1, 1.8%), whereas the Omin-N content was higher in paddy soils (200 mg kg-1, 8.9%) than in upland soils (108 mg kg-1, 4.4%). No differences due to land use were observed in the stable N fraction. In contrast, differences due to soil types which were not observed in the available fraction were clearly observed in the stable fraction (Ifix-N and Osta-N), Le. the lfix-N content was higher in non-volcanic soils (156 mg kg-1, 10.0%) than in volcanic soils (54 mg kg-1, 1.6%) whereas the Osta-N content was higher in volcanic soils (3,639 mg kg-I, 93.0%) than in non-volcanic soils (1,632 mg kg-1, 80.1%). Accordingly, the 42.4% of variance of the lfix-N content was explained by the clay and Alo contents and 48.1% of variance of the Osta-N content by the Alo content. These findings showing that, in Japanese agricultural soils, the available N fraction was strongly affected by the land use, whereas the stable N fraction was mainly determined by the soil types, should be taken into account in the management of soil N in agricultural practices and N dynamics in agricultural fields.

Effect of plant growth on the distribution and forms of soil nutrients in the rhizosphere

Abstract The effect of plant growth on the distribution and forms of soil nutrients in the rhizosphere was studied by growing plants in rhizoboxes. An experiment was carried out in a growth chamber for 17 d with three treatments, i.e. maize (Zea mays L.), kidney bean (Phaseolus vulgaris L.), and no plants. After the experiment, soil samples were collected up to about 50 mm from the central compartment (C. C.) in which roots were allowed to grow, and analyzed for the soluble, exchangeable, and total amounts of nutrients. Plant samples were also analyzed for their nutrient contents. The pattern of nutrient distribution in the rhizosphere varied among the types and forms of elements. In both maize and kidney bean, the concentrations of soluble P, K, and N decreased significantly at the C.C., up to 4 mm and up to 10 mm from the C.C., respectively. The magnitude of their depletion reflected their rate of diffusion in soil. The concentration of exchangeable K decreased significantly up to 2 mm from theC.C., whereas those of exchangeable Ca and Mg increased within 1 mm from the C.C. The total amount of nutrients, however, did not change significantly for each element. The depletion of soluble P and K mainly around the C.C. indicated the presence of their diffusion toward the root surface. Their uptake was larger than the apparent decrease of their soluble forms, suggesting that their depletion was compensated by intensive replenishment from the soil solid phase. The concentrations of N, Ca, and Mg, on the other hand, markedly decreased up to the end of the rhizobox, indicating the presence of mass flow. The depletion was proportional to the rate of transpiration by plants.