Shinya Funakawa

Characterization of the frayed edge site of micaceous minerals in soil clays influenced by different pedogenetic conditions in Japan and northern Thailand

Abstract Radiocesium interception potential (RIP), a quantitative index of a frayed edge site of micaceous minerals, was investigated on test clay minerals (illite, kaolinite, montmorillonite and vermiculite) and soil clays formed under different pedogenetic conditions in the Kinki district of Japan and in northern Thailand to elucidate the effect of pedogenetic weathering on the amount of frayed edge site of micaceous minerals. A frayed edge site is defined as the wedge-shaped intermediate zone between non-expansible (1.0 nm) and hydrated (1.4 nm) interlayers, on which Cs is selectively adsorbed. The test clay minerals demonstrated unique RIP values closely associated with their charge characteristics. Very small RIP in non-micaceous test minerals (0.006 mol kg−1 in kaolinite; 0.1 mol kg−1 in montmorillonite) supported the fact that negative charges in these minerals do not show selective adsorption of 137Cs. Large RIP values in vermiculite (25.9 mol kg−1) compared with illitic minerals (4.3 mol kg−1 in silt size; 11.8 mol kg−1 in clay size) suggested that the frayed edge site increased as the expanded layer formed in the micaceous minerals. In northern Thailand soil clays, the absence of a vermiculitic expanded layer was indicated. Periodic wet–dry conditions may restrict K depletion from micaceous minerals in the region. It is concluded that micaceous minerals were weathered without layer expansion and, therefore, the amount of the frayed edge site was regulated by the content of micaceous minerals in northern Thailand. In Japanese soil clays, large RIP values were found in the EB and Bs horizons of a Podzodic profile (SW1), which had large vermiculitic expanded layers like the test vermiculite. However, the RIP values drastically decreased from the Bs to E horizon, maintaining a high vermiculitic layer charge. Thus, intensive weathering in highly acidic soils in Japan might reduce the frayed edge site.

Ecological study on the dynamics of soil organic matter and its related properties in shifting cultivation systems of Northern Thailand

Abstract There is a large number of hill people in northern Thailand, who practices shifting cultivation. In order to analyze the soil ecological problems involved in the transition from traditional shifting cultivation to more intensive upland farming, the authors carried out comparative studies on the dynamics of organic matter and its related properties in soils both in the traditional shifting cultivation systems adopted by Karen people and more intensive upland farming practiced by Thai and Hmong people in the area. The contents of organic matter and available N in the surface 10 cm layers of soil from the fields continuously cultivated were lower than those in soils under prolonged fallow (more than 10 y) or natural forest. Based on the rate of soil respiration, the amount of organic matter decomposed within 1 y was estimated to reach nearly 10% of that stored in the upper 50 cm layers of the soil profile in the upland crop fields. These results indicate that the organic matter-related resources mar...

Spatial prediction of soil organic matter in northern Kazakhstan based on topographic and vegetation information

Abstract This study aimed to improve the accuracy of spatial prediction for soil organic matter, potential mineralizable carbon (PMC) and soil organic carbon (SOC), using secondary information, namely topographic and vegetation information, in northern Kazakhstan. Secondary information included elevation (ELEV), mean curvature (MEANC), compound topographic index (CTI) and slope (SLOPE) obtained from a digital elevation model, and enhanced vegetation index (VI) values obtained from a moderate resolution imaging spectroradiometer (MODIS). The prediction methods were statistical (multiple linear regression between soil organic matter and secondary information) and geostatistical algorithms (regression-kriging Model-C and simple kriging with varying local means [SKlm]). The VI, ELEV and MEANC were selected as the independent variables for predicting PMC and SOC. However, MEANC showed an opposite effect on PMC and SOC accumulation patterns. Model validity revealed that SKlm was the most appropriate method for predicting PMC and SOC spatial patterns because model validity revealed the smallest errors for this method. Maps from the kriged estimates showed that a combination of secondary information and geostatistical techniques can improve the accuracy of spatial prediction in study areas.

Biodegradation of low molecular weight organic compounds and their contribution to heterotrophic soil respiration in three Japanese forest soils

Low molecular weight (LMW) organic compounds in soil solution could be important substrates for heterotrophic soil respiration. The importance of LMW organic compound mineralization in heterotrophic soil respiration needs to be confirmed for different types of soils. The concentrations of LMW organic compounds in soil solution and mineralization kinetics of 14C-radiolabelled glucose, acetate, oxalate and citrate were studied in three Japanese forest soils (Andisol, Spodosol and Inceptisol) with varying adsorption capacities. Based on those results, the fluxes of LMW organic compound mineralization and their magnitude relative to heterotrophic soil respiration were quantified. Monosaccharides and organic acids comprised on average 5.9–11.2% and 0.9–1.4% of dissolved organic carbon in soil solution, respectively. Monosaccharide mineralization make up 49–74% of heterotrophic (basal) soil respiration at the soil-profile scale, while organic acid mineralization accounts for between 5% (Andisol) and 47–58% (Spodosol and Inceptisol) of heterotrophic soil respiration. The mineralization of LMW organic compounds is a substantial fraction of heterotrophic soil respiration regardless of soil type, owing to their rapid and continuous production and consumption. The specific contribution of organic acid mineralization to heterotrophic soil respiration varies depending on soil adsorption capacities, namely iron and aluminum oxides.

Soil ecological study on dynamics of K, Mg, and Ca, and soil acidity in shifting cultivation in northern Thailand

Abstract Soil degradation caused by excessive land use is presently one of the major constraints on sustainable agriculture in the mountainous area of northern Thailand. In order to obtain basic information about soil fertility problems involved in the transition from traditional shifting cultivation to more intensive upland farming, the dynamics of K, Mg, and Ca, and soil acidity in the farming systems of both Karen and Hmong/Thai peoples were investigated. In the fields that lay fallow for more than 5 y, the soils were highly acidic and poor in exchangeable bases, mainly due to the fact that the fallow vegetation rapidly absorbed inorganic bases (K, Mg, and Ca) in the soils. In the fields both under fallow and cropping within 3 y after the slash and burn practice, the high acidity observed in the soils at the fallow stage seemed to be alleviated by ash input with high alkalinity. The aboveground biomass ranged from 9 to 10 t ha−1 in the 8 y fallow field and the sum of inorganic bases and alkalinity, whi...

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.

Dynamics of microbial biomass nitrogen in relation to plant nitrogen uptake during the crop growth period in a dry tropical cropland in Tanzania

Abstract Soil microbes are considered to be an important N pool in dry tropical croplands, which are nutrient poor. To evaluate the N contribution of soil microbes to plant growth in a dry tropical cropland, we conducted a maize cultivation experiment in Tanzania using different land management treatments (no input, plant residue application, fertilizer application, plant residue and fertilizer application, and non-cultivated plots). Over 104 experimental days, we periodically evaluated the microbial biomass N and C, plant N uptake, microbial respiration in situ and inorganic N in the soil. A significant amount of inorganic N was lost in all of the treatment plots as a result of leaching during the initial 60 days and inorganic N remained low thereafter (∼20–35 kg N ha−1 : 0–15 cm), whereas soil microbial respiration substantially decreased because of soil drying after 60 days (grain-forming stage). During the grain-forming stage (60–104 days), we found a distinct effect of plant N uptake on soil microbial dynamics, although we did not observe an obvious effect of plant residue and/or fertilizer application; microbial biomass N decreased drastically from 63–71 to 18–33 kg N ha−1 and the microbial biomass C : N ratio simultaneously increased (>10-fold) in all maize-cultivated plots; these features were not observed in the non-cultivated plot. Plant N uptake over the same period was 26.6–55.2 kg N ha−1, which was roughly consistent with the decrease in microbial biomass N. These results indicate that strong competition for N occurred between soil microbes and plants over this period and N uptake by plants prevented microbial growth. Thus, we concluded that soil microbes contribute to plant growth by serving as a N source during the grain-forming stage in dry tropical cropland.

Nutritional Environment of Tropical Peat Soils in Sarawak, Malaysia Based on Soil Solution Composition

Abstract It has been considered that natural peat soils and swamp forest ecosystems in the tropics are quite oligotrophic. This concept seems to be related to the low mineral contents in the soil solid phase of the peat soils. However, some nutritional elements such as K, Mg, Ca, and/or P may be abundant in the soil solution phase and could easily migrate in peat soils. In order to analyze the nutritional environment of peat soils, chemical composition of the soil solid phase and soil solution was compared. This study was carried out in Naman Forest Reserve, Sibu and in/around Sg. Talau Peat Research Station, Mukah, Sarawak, Malaysia. In both areas, each of the three study sites with a different depth of underlying mineral layer was selected for sampling of soil and soil solution. All the soils studied except for one shallow peat profile were classified into Oligotrophic peat based on Fleischer’s criteria. The soil solution collected monthly showed the following characteristics in its composition. 1. Conc...

Carbon dioxide emission derived from soil organic matter decomposition and root respiration in Japanese forests under different ecological conditions

Abstract Soil chambers with 3 types of soil treatment were used to analyze the environmental factors controlling carbon dioxide (CO2) emission in forest soils of Japan and to separately determine CO2 emission from root respiration, microbial decomposition of organic matter in the O layer and in the mineral soil layers. Soil chambers were installed at the Kyoto, Miyazu-Oak, Miyazu-Cedar, Miyazu-Beech and Nobeyama sites; the sites differed from each other in soil temperature, vegetation and parent materials. The soil treatments applied at each of the 5 sites were as follows: (1) control plot, (2) O- plot with removal of the O layer, (3) root- plot with the suppression of root respiration by inserting the chambers to a depth of 20 cm and sealing the bottom. The CO2 emission levels at all sites were significantly correlated with soil temperature, but not with soil moisture levels. The annual rates of soil organic matter decomposition simulated based on the automatically recorded soil temperature were 5.1, 4.0, 5.2, 5.5 and 3.4 Mg C ha−1 at the Kyoto, Miyazu-Oak, Miyazu-Cedar, Miyazu-Beech and Nobeyama sites, respectively. These rates were influenced by soil temperature, litter fall rates and the carbon stocks. In contrast, the ratio of the annual rate of root respiration to the annual rate of soil respiration decreased as soil temperature decreased. Based on the carbon budget, the Miyazu-Cedar and Nobeyama sites appeared to have lost their soil carbon stock. For more accurate analysis, methods for the direct measurement of the input rate of root litter should be developed.

Salt-affected soils under rice-based irrigation agriculture in southern Kazakhstan

Abstract The development of large-scale irrigation agriculture in the arid region of Central Asia, which was initiated in the 1960s under the former Soviet Union, has resulted in soil salinization in irrigated farms and their vicinity. In order to establish an appropriate countermeasure against soil salinization, we investigated the distribution pattern of salt-affected soils and their forming processes in rice-based cropping fields and their surroundings in four former state farms in the R. Ili and R. Syr-Darya basins in southern Kazakhstan. In the farm along R. Ili, two types of distribution patterns of salts in the soil profiles were observed. The first process was observed in cultivated and uncultivated fields adjacent to the irrigation canal, and characterized by an accumulation of gypsum and/or soluble salts at/near the soil surface, suggesting an upward movement of water with a high concentration of salts. The second process was observed in uncultivated fields far from canals. Salt accumulation was observed in deeper horizons in combination with a low-salt, alkalinized layer on top, indicating that the soils were formed by leaching with a positive reaction for residual sodium carbonate. In the surface soil layer under upland cropping, amounts of soluble cations was 16.6±3.4 (SE) cmol c kg −1 in the farm located in the lower part of R. Syr-Darya, which was much higher than that in the farm along R. Ili (4.8±0.4 cmol c kg −1 ). In the latter, the annual rate of salt accumulation during the first year of upland cropping was roughly estimated to 45 kmol c ha −1 year −1 , while in the second year the accumulation was about 15 kmol c ha −1 year −1 . The contents of soluble salts decreased to 2.0±0.6 cmol c kg −1 during the period of rice cultivation in the farm along R. Ili, showing that water-logging in this phase was effective to leach out the salts accumulated during the upland phase. The soils in the paddy field in the R. Syr-Darya basin showed, however, still a high salinity level, i.e. 5.6±1.2 cmol c kg −1 , presumably because of the incomplete drainage conditions. These results suggested that the rice-based irrigation agriculture studied is sustainable provided that an adequate supply of irrigation water and an appropriate drainage system are available.