Ueru Tanaka

Characterization of the organic components of an Alfisol and a Vertisol in adjacent locations in Indian semi-arid tropics using optical spectroscopy, 13C NMR spectroscopy, and 14C dating

Organic components of an Alfisol and a Vertisol in adjacent locations in Indian semi-arid tropics were characterized using chemical analysis, photometric and high resolution solid-state 13C nuclear magnetic resonance (NMR) spectroscopies, and 14C dating. The organic carbon contents of the Alfisol (0.50-0.25%) were about half the ones of the Vertisol (0.69-0.48%). Among the organic components, fulvic acids were found to be the major constituents, about 80–90% in the Alfisol and 70% in the Vertisol. These figures suggested faster organic decomposition in the Alfisol. The color intensities (K600/C) of humic acids of the Alfisol increased from the surface through deeper layers, while those of the Vertisol remained constant in all the layers. The 13C NMR measurements on the humic acids of both soils suggested the presence of polymethylene-, methyl-, N-methyl-, O-methyl-, dioxygenated-, O-alkyl-, aromatic-, phenolic or quaternary-, and carboxyl carbons. The Alfisol humic acid samples were characterized by a higher content of unsaturated (110-0 ppm) carbons and a lower content of quaternary ( 145-120 ppm) carbons than those of the Vertisol. Radiocarbon dating showed that the humic acids of the Alfisol were of modem (10 cm) through 2520 yr BP (40 cm) years old, while those of the Vertisol were in a narrower range of 4650 yr BP (10 cm) through 5440 yr BP (40 cm). Close relationships among radiocarbon dating, photometric, and NMR spectrometric characteristics of humic acids were suggested.

“Fallow Band System,” a land management practice for controlling desertification and improving crop production in the Sahel, West Africa. 1. Effectiveness in desertification control and soil fertility improvement

Wind erosion is a major contributor to desertification in the Sahel. Although three effective countermeasures for wind erosion (i.e. ridging, mulching with post-harvest crop residue, and windbreaks) have been proposed, they are not practical for Sahelian farmers. Therefore, we designed a new land management practice, termed the “Fallow Band System,” which can be used for both controlling wind erosion and improving soil fertility and crop production. This method does not impose additional expense and labor requirements on Sahelian farmers who are economically challenged and have limited manpower. The objective of this study was to evaluate the effects of this system on wind-erosion control and soil-fertility improvement. We conducted field experiments at the International Crops Research Institute for the Semi-Arid Tropics West and Central Africa and showed that (i) a fallow band can capture 74% of wind-blown soil particles and 58% of wind-blown coarse organic matter, which suggests that it can effectively control wind erosion, (ii) the amount of soil nutrients available for crops in a former fallow band was increased by the decomposition of trapped soil materials containing considerable amounts of nutrients, and (iii) the amount of soil water available for crops in a former fallow band was increased by the trapped wind-blown soil materials through improvement of rainwater infiltration into surface soil. These results lead to the conclusion that the “Fallow Band System” can be useful for preventing desertification and improving soil fertility in the Sahel, West Africa.

Sediment catcher to trap coarse organic matter and soil particles transported by wind.

Wind can erode fertile topsoil and reduce soil fertility. Evaluating the effect of wind erosion on soil fertility is crucial to achieve sustainable agriculture in areas suffering from desertification caused by wind erosion. To estimate soil loss and associated soil nutrient loss by wind erosion, flux of coarse organic matter (COM) (defined here as free organic debris larger than 200 µm) and soil particles (defined as the other soil components) must be measured separately. This is because their modes of transport are different, and COM plays a prominent role in soil nutrient dynamics in some semiarid zones where COM accounts for a large percentage of the total soil carbon. Because the Big Spring Number Eight (BSNE) sampler can trap both COM and soil particles 0.05 m above the surface, we designed a sediment catcher, the Aeolian Materials Sampler (AMS), to trap these components below 0.05 m. This device can be manufactured easily at low cost. AMS performance was tested by wind tunnel experiments over a range of wind velocities typically observed in erosive storms and with six incident wind angles because the AMS is a buried-type sampler that is unable to rotate toward the wind. The trapping efficiency of the AMS for COM and soil particles was not 100%, but it can be calibrated easily using wind data. Therefore, we can estimate the mass flux of COM and soil particles and evaluate the effect of wind erosion on soil fertility using the AMS with the BSNE sampler.

Morphological characteristics of soil surface crusts formed under simulated rainfall

Abstract Morphological surface characteristics of soil samples, subjected to simulated rainfall with an intensity of 4.48 mm/min for different periods of time, were observed and quantified by applying the image analyzing technique to the binary image of the thin section specimens (TS-IA method). In the microscopic observation, two types of crust morphology were recognized; in one type, the crust consisted of a densely packed layer of finer particles with a “seal skin” (McIntyre 1958) of the uppermost surface, and in the other type, the crust consisted of a relatively dense layer of clogged smaller aggregates, designated as “washed-in layer” (McIntyre 1958), underlying the coarse aggregates and sand grains. Operationally, a “crust” is defined as a zone that extends continuously with a certain value of low apparent porosity (AP). By setting the critical value arbitrarily at 5%, in this study, the morphological characteristics of the soil crusts were quantified, in terms of the sum of the thickness of low AP...

Mechanisms and Processes of Crust Formation on Artificial Aggregates : III. Relations between Natural Rainfall Characteristics and Degree of Crusting

Crust formation process initiates from aggregate disinategration occurred through the combined effects of inherent soil properties and external actions. Rainfall plays a major role in determining the moisture conditions of the soil surface and in triggering aggregate disintegration mainly through slaking and the impact off raindrops. To analyze the relations between rainfall characteristics and crust formation, three artificially granulated aggregates were exposed to natural rainfall events. The rainfall characteristics were expressed in terms of the distribution pattern of rainfall intensity, I 10min; mean weighted drop diameters, D n; raindrop concentration, N Dn,; rainfall energy, Et;and kinetic energy, KE; as well as conventionally used parameters, such as total amount and mean intensity of rainfall. The degree of crusting was evaluated in terms of the water permeability and morphological observation just after the rainfall treatment. Based on a comparison of the rainfall characteristics and ...

Technical Note: Aeolian Materials Sampler for Measuring Surface Flux of Soil Nitrogen and Carbon During Wind Erosion Events in the Sahel, West Africa

In the Sahel, determining the effects of wind erosion on soil fertility and soil carbon balance is crucial for achieving sustainable agriculture and for carbon sequestration, respectively. We designed the Aeolian Materials Sampler (AMS) to measure the surface flux of soil nitrogen and carbon, which limit crop production as well as water in the Sahel. The AMS should not be used alone, but with the Big Spring Number Eight (BSNE) sampler, which is a quasi-isokinetic sampler. We examined the performance of the AMS in estimating the surface flux of soil nitrogen and carbon by conducting wind-tunnel and field experiments. In the former experiment, we measured the trapping efficiency of the AMS for nitrogen and carbon content in coarse organic matter (COM) and soil particles. We observed that the AMS allows estimation of the surface flux of soil nitrogen and carbon associated with the movement of COM and soil particles; wind data and empirical equations were used for the estimation. In the field experiment, we assessed the contribution of the inherent error of the AMS to the total measurement error and found that the inherent error was negligible and did not increase the total measurement error in the estimation of the surface flux of soil nitrogen and carbon. Therefore, we concluded that the combination of the AMS and the BSNE sampler could be effectively used to evaluate the effects of wind erosion on soil fertility and soil carbon balance in the Sahel.

Mechanisms and processes of crust formation on artificial aggregates: I. Effect of Initial Moisture Conditions on Aggregate Stability and Crusting

Assuming that the degree of aggregate disintegration or stability is affected by the initial moisture conditions, and that the uppermost zone of the soil surface, where a crust is formed, is subjected to the fluctuations of the moisture content under field conditions, the relations among the initial soil moisture conditions, aggregate stability and crust formation should be analyzed in order to elucidate the mechanisms and processes of crusting. Since rainfall is the major factor involved in the disintegration of soil aggregates at the surface through the slaking and impact actions, we determined the degree of aggregate disintegration with slaking and of crusting formed by simulated rainfall treatment as follows; intensity, 4.48 mm min−1; water drop diameter, 2.17 mm; rainfall duration, 2 and 5 min, using artificially granulated aggregates, 1.0 to 2.0 mm in diameter, under moisture conditions preliminarily adjusted at definite levels of matric suction, 0.98 kPa to 9.81 MPa. The results are summar...

Mechanisms and Processes of Crust Formation on Artificial Aggregates : II. Effect of Slaking and Impact of Rain Drops on Crusting under Different Moisture Conditions

Abstract Simulated rainfall treatment (intensity^4.48 mm min−1; drop diameter, 2.17 mm; falling height, 1.5 m;. and duration, 2, 5, 8, 12 min) was applied to three artificially granulated aggregates, 1.0 to 2.0 mm in diameter, the initial moisture content of which was adjusted preliminarily to definite levels of matric suction, 0.98 ×10−3 to 9.81 MPa. Degree of crusting was measured in terms of negative logarithm of hydraulic conductivity, —log K value (Tanaka et al. 1995: Soil Sci. Plant Nutr., 41, 263-273). The effects of slaking and impact of rain drops on crust development were estimated by using the —log K values obtained after simulated rainfall treatment for 2 and 5 min under different initial moisture conditions. The mechanisms and processes of crust formation under different moisture conditions were discussed. The results are summarized as follows: 1) The action of rainfall involved “impact” and “slaking” as the major factors. The slaking action was further divided into “weak slaking” and “rapid ...

Housing Conditions of a Lagoon Village in a Flood-prone Area of Central Vietnam

Abstract The climatic and geographic features of central Vietnam frequently contribute to annual floods, and several disastrous floods have been recorded in the last few decades. The most recent and disastrous flood, in 1999, is still memorable within the affected area, due to the magnitude of catastrophe inflicted by floodwaters. However, the flooding effects in rural areas are not often reported in detail. This study aims to clarify flood-adaptation measures and the vulnerability of housing conditions in the flood-prone area, based on a field survey of a lagoon village. The surveyed houses can be classified into four different types that have similar spatial layouts. Most of the surveyed houses show characteristics of adapting well to annual floods; for example, floor levels are conventionally raised to adjust to the height of annual floodwaters in each location. Nonetheless, housing conditions are still vulnerable to future disastrous floods, as efficient flood-prevention features—such as the provision of two-story durable housing—often prove too expensive for most villagers. Thus, villagers need to develop other measures to prepare themselves better for disastrous flooding.

Evaluation of crusting susceptibility of some Japanese soils based on water permeability and morphology of crusts

Abstract Crusting susceptibility of 19 soils collected from upland fields in Hokkaido, Kinki, and Shikoku districts was evaluated based on microscopic observations, morphological parameters using the thin section-image analyzing technique (Tanaka and Kyuma 1992: Soil Sci. Plant Nutr., 38, 369-373) and water permeability after subjecting the samples to simulated rainfall. The morphology of the soil surface after the simulated rainfall treatment was classified into four types: type A with less disintegrated aggregates, thus, less crusted; type B with a relatively dense band, so-called “washed-in layer” (McIntyre 1958: Soil Sci., 85, 185-189), composed of disintegrated small aggregates at a few millimeters below the surface; type C with densely compacted layer and a “seal skin” (Mclntyre 1958: Soil Sci., 85, 185-189) composed of disintegrated fine particles at the surface; type D with morphological features similar to those of type C but lacking a “seal skin.” Water permeability parameter, —log K value, show...