Search

This study investigated general physicochemical properties of tea garden soils at the alluvial plain of Cong River in Tan Cuong commune, Vietnam. Four gardens were selected as study sites on three ...

The morphological and chemical properties of homegardens in the beach ridges with interspersed swales (BRIS) soils were evaluated in order to find a clue for developing sustainable agricultural management. Field survey and soil sampling were conducted at the homegardens and secondary forests in Sungai Ular Village and in the experimental farm of Malaysian Agriculture Research Institute (MARDI), Cherating Station. Chemical fertilizers including ash, charcoal waste and plant litter were applied to the homegardens in both the inland-ward area (HG-I) and in the shoreline area (HG-S). Manure was applied in HG-I and seafood waste from fish processing was buried in the soils in HG-S. High correlation was found between total carbon (T-C) and cation exchange capacity (CEC), indicating soil organic matter was the determinant factor for CEC in the very sandy BRIS soils. The levels of T-C, total nitrogen (T-N), and CEC at 0–10 cm in HG-I in parallel with increasing ages of homegardens. The soils in 0–10 cm an...

Little is known about the effect of soil disinfection on bacterial communities. Soils were treated with an effective chemical fumigant chloropicrin and biofumigant mustard greens (Brassica juncea). While mustard greens did not affect the soil bacterial community structures very much, chloropicrin greatly reduced soil biomass and bacterial species richness. Chloropicrin also influenced the bacterial community structure, making the phylum Firmicutes dominant by occupying about 75%. In more than two months, the proportion of Firmicutes was reduced to the basal level, and the phyla Bacteroidetes and Proteobacteria became dominant. Since mustard greens worked as carbon sources for soil reduction, soils were treated with wheat bran and a low concentration of ethanol. Soil reduction with wheat bran and ethanol did not influence the soil bacterial community structures. Beta diversity analyzed by Principal Coordinate Analysis showed that bacterial communities in the soils except chloropicrin-applied soils formed a cluster. All together, biofumigant mustard greens, a probable substitute for chloropicrin, were demonstrated to cause much less damage on soil bacterial community than chemical chloropicrin.

Soil bacterial community structures in terraced rice fields and abandoned lands in a hilly and mountainous area were analyzed using 16S rRNA gene sequences. The DGGE band patterns of each soil were similar. Based on pyrosequencing data, the richness and diversity of bacterial species were slightly higher in paddy fields than in other soils. A beta-diversity analysis clearly indicated that the bacterial community structure in paddy fields differed from those in non-paddy field lands and crop fields that had not been used as a paddy field. These results may reflect the history of land use.

In Vietnam, the Co Dinh mine is the largest chromite mine in the country. Mining, ore dressing and disposal of the tailings provide obvious sources of heavy metal contamination in the mine area. The present study examined the influence of chromite mining activities on the adjacent lowland paddy field by investigating heavy metal and As levels in the mine tailings, sediments, paddy soils and water. At paddy fields located near the mine tailings, the total contents of Cr, Co and Ni were 5,750, 375 and 5,590 mg kg−1, and the contents of their water-extractable form were 12.7, 1.16 and 32.3 mg kg−1, respectively. These results revealed severe contamination of lowland paddy soils with Cr, Co and Ni as a result of mining activity, suggesting serious health hazards through agricultural products, including livestock in this area. The principal source of the pollution was sediment inflow owing to the collapse of the dike, which was poorly constructed by heaping up soil. Moreover, water flowing out from th...

Soil fertility status under various types of upland farming was evaluated in a village in Mae Taeng District of Chiang Mai Province in northern Thailand. The farmlands were on sloping land in a transitional zone of hill evergreen and mixed deciduous forests (800-1000 m a.s.l.). Miang tea (Camellia sinensis var. assamica ), traditionally cultivated as the sole main cash crop, has been replaced by other cash crops. The studied soils originated from granite (n=30), limestone (n =16), and shale (n =6). Clay minerals were composed mainly of kaolin minerals in the granite soils and quartz, chlorite, gibbsite, mica, and kaolin minerals in the limestone and shale soils. Soil texture classes differed among soil types. However, granite and shale soils showed similar chemical properties to each other with an acidic nature and lower levels of exchangeable bases. Irrespective of the parent material, the CEC values were correlated with soil organic matter contents but not with clay contents. The levels of soil organic matter and the resulting CEC as well as ECEC values were higher in the limestone soils than in the granite and shale soils. These results suggest that higher negative charges in the limestone soils were derived from soil organic matter and that these charges developed under higher soil pH conditions. The C/ N ratios of the limestone soils were lower than those in the granite soils and shale soils, reflecting the well-decomposed status of soil organic matter. The granite soils were classified into three groups based on their physicochemical properties: foresttype soils (remnant forest, secondary forest, miang tea garden and lychee orchard), soils of annual crop fields, and soils of the home gardens. The forest-type soils were characterized by their strong acidic nature with lower contents of exchangeable bases and available P. Soils of the annual crop fields and those of home gardens showed a less acidic nature and nutrient accumulation occurring as a result of fertilizer application. However, a dif ference between these soils was that while the annual crop fields possessed preferable soil physical properties for crops caused by tillage management, soils of home gardens were subjected to compaction throughout soil profiles. In contrast to granite soils, the effects of different land uses on soil fertility were not evident in limestone soils. However, the annual crop fields and orange orchards had low total C and total N, engendering lower CEC values. Although the available P of these soils was high because of fertilizer application, fertilizer N in the annual crop fields seemed not to contribute to a buildup of total N and ammonium N. Both in lychee orchards with the granite soils and orange orchards with limestone soils, fertilizer P had accumulated around trees where fertilizer was usually applied. For shale soils, the subsurface soils under the oolong tea gardens (Camellia sinensis var. sinensis) were rich in total C and N and less compacted than soils of other land uses. Results show that dif ferent farming practices affected soil fertility status depending on soil types with different parent materials. 186 Sota TANAKA, Thanakorn LATTIRASUVAN, Kenji NAKAMOTO, Chalathorn SRITULANON and Katsutoshi SAKURAI

A pot culture experiment was conducted to investigate the effects of amorphous iron-(hydr)oxide (Am-FeOH) amendments on arsenic (As) availability and its uptake by rice (Oryza sativa L. cv. BR28) irrigated with As-contaminated water. A rhizobag system was established using 3.5 L plastic pots, each containing one central compartment for plant growth, a middle compartment and an outside compartment. Three levels of laboratory-synthesized Am-FeOH (0, 0.1 and 0.5% w/w) were used to amend samples of the As-free sandy loam paddy soil placed into each compartment of the rhizobag system. The soils were submerged with a solution containing 5 mg L−1 As(V). Two-week-old rice seedlings were planted in the central compartments and cultured for 9 weeks under greenhouse conditions. The addition of 0.1% Am-FeOH to the soil irrigated with As-contaminated water improved plant growth, reduced the As concentration in the plants and enhanced Fe-plaque formation on the root surfaces. Analysis of soil solution samples ...

This study was conducted in order to evaluate the vegetation conditions and soil fertility status of fallow lands under intensive shifting cultivation systems in the Engkari river area in Sarawak, Malaysia. The shifting cultivation by the several Iban communities selected at Engkari area for upland rice farming were currently being conducted with 2 to 7 years of continuous cropping followed by 1 to 6 years of fallow with application of chemical fertilizers and agrochemicals. Since agricultural management methods and land productivity under the current shifting cultivation systems conducted by the Iban farmer were our concerns, we carried out vegetation and soil surveys on fallow lands of which suitability for rice cropping using shifting cultivation had been classified by Iban landowners from their knowledge of vegetation conditions; 20 suitable and 20 unsuitable sites were analyzed. The results of our vegetation survey showed no substantial differences between suitable and unsuitable sites in the species composition and the sizes of tree species, as measured by the stem diameter at breast height (DBH). The plant density of grass and fern groups tended to be higher in most of the sites even after extensive fallow duration. As compared to our previous studies, the DBH of the trees in most of the Engkari area study sites was small even after extensive fallow duration. The soil properties in the study sites could be characterized by a strongly acidic nature with low levels of exchangeable bases. No substantial differences were found in the soil properties in terms of site suitability and fallow duration. Our results suggest that the rationality of farmers’ traditional knowledge related to vegetation-based site selection is no longer applicable under intensive shifting cultivation practices in the Engkari area. Considering the high acidity and poor nutrient contents of the soils, as well as poor aboveground biomass added to soil as ash during burning, certain measures will be necessary for the farmers in the Engkari area to continue rice cropping through the intensive shifting cultivation system. These include effective types of fertilizer and appropriate application methods as well as countermeasures to soil erosion in order to prevent the loss of fertilizer nutrients from soil ecosystems.

This study assessed the arsenic and heavy metal contaminations of agricultural soils around the tin and tungsten mining areas in Dai Tu district in northern Vietnam. Among the examined elements, high total contents of As and Cu were found in the agricultural fields at both tin and tungsten mining sites. Although the major part of the accumulated As and Cu were bound by various soil constituents such as Fe and Mn oxides, organic matter, and clay minerals, increases in water soluble As and Cu were observed, especially for the paddy fields. The results suggest that, in the studied area, As and Cu dispersion from their pollution sources into farmlands is mainly via fluvial transportation of mine waste through streams that cross the paddy fields around the tin mining area, and soil erosion at the tea fields located at lower positions of the slope in the tungsten mining area.

The role of arbuscular mycorrhizal fungus (AMF) on biotransformation of arsenic (As) in the rhizosphere of sunflower (Helianthus annuus L.) was studied in a rhizobag system with As-contaminated soil. The treatments consisted of a combination of two levels of AMF (Glomus aggregatum) inoculation (–AM and +AM) under sterile and non-sterile soil conditions (S and NS). Each treatment was designated as –AM/S, –AM/NS, +AM/S and +AM/NS. Sunflower seedlings were cultured in the rhizobag for 6 weeks. Rates of root AMF colonization in +AM treatments were approximately 40% and 0% in –AM/S treatment. The AMF inoculation reduced As toxicity symptoms and improved plant growth. Shoot As, but not the root As, concentrations were reduced by AMF inoculation. Shoot and root P concentrations increased in +AM treatments regardless of soil sterilization. Analyses of water soluble (WS) As in the soils at the end of the cultivation indicated that the amount of WS-arsenite (AsIII) was higher in the central compartment com...

Soil properties under secondary forests were studied in relation to vegetation conditions to clarify the site selection method for shifting cultivation of the Iban in Sarawak, Malaysia. Soils and vegetation were surveyed at 25 suitable sites and 17 unsuitable sites for shifting cultivation, classified by the landowners based on their perceptions through knowledge of vegetation condition. Principal component analysis classified soil properties into three principal components. The first was soil texture and organic matter with high factor loadings of clay content, cation exchange capacity, total C, and total N, and, to a lesser extent, exchangeable K. These properties were little affected by the fallow duration and site suitability. Clay content was regarded as one of important factors related to the levels of organic matter and nutrient retention capacity of the soils. The second component reflected soil acidity and exchangeable bases with high factor loadings of pH, exchangeable Ca and Mg, exchangeable Al, and Al saturation. These properties reflected the remnant effects of ash addition and fallow duration. However, no clear differences were apparent in these properties in terms of site suitability. The third component was linked to N availability, including the C/N ratio and exchangeable NH4. The N availability was higher at suitable sites than at unsuitable sites. At suitable sites, N availability tended to be higher with increasing fallow age. The N availability showed a statistically significant correlation with the site score of the first axis obtained from correspondence analysis of plant density, suggesting a strong relationship between N availability and vegetation condition. That relationship was attributable to depletion of the available N of the soils during cropping and at the initial fallow stage, as well as to improvement of N availability of soils with increasing length of the fallow period. This finding related to N availability was consistent with farmers' criteria for fertile land: leaves of trees in fertile land should be dark green. The presence of some specific plant species might be correlated with levels of available P and soil hardness. Results of this study show that the Iban farmers' vegetation-based site-selection method might reflect the ability of secondary forest ecosystems to supply nutrients for rice plants through burning practices.

Sustainability of the local shifting cultivation practice in the mountainous region of Northern Laos was investigated. Due to low fertility of the soils derived from shale and its strongly weathered and acidic nature in the eastern side of the Nam Khan River watershed, shortening of the fallow period to produce enough amount of upland rice for the local population would not be sustainable any more. On the other hand, the eroded materials from limestone range were added to the soils in the western side of watershed which made the soil more fertile. Based on the calculated population capacity by Carneiro's equation, a system with 2- or 3-year fallow for 1-year cultivation can be the maximum to afford the current population. To make the shifting cultivation system more sustainable, introduction of fallow system with a tree species, paper mulberry (Broussonetia papyrifera) could be a good option to be proposed.

Experimental shifting cultivation was carried out at two sites, Niah and Bakam in Sarawak, Malaysia. The plots (10 × 10 m2) were treated with burning of vegetation biomass (fuel), amounting to 100, 200 and 300 Mg ha−1 with an untreated control at the Niah site and 20 and 100 Mg ha−1 with an untreated control at the Bakam site. At the Niah site, the soils were acidic with a light clay texture. The levels of pH, exchangeable bases and available P of the soils at the depth of 0–5 cm increased by burning while those of exchangeable Al and Al saturation decreased. The changes tended to be more appreciable in the plot treated with fuel at the rate of 300 Mg ha−1 than in the other plots. Based on a comparison between ash alkalinity and the difference in the content of exchangeable Al at 100 d after burning and before burning, it was assumed that 60% of the alkalinity contained in ash was consumed for inactivating exchangeable Al at the depth of 0–5 cm, which resulted in minimal changes in the soil properties in ...

The effects of burning on the levels of soil organic matter, soil nitrogen, and soil microbial biomass were studied by carrying out experimental shifting cultivation at two sites, Niah and Bakam in Sarawak, Malaysia. Vegetation biomass was burned in plots (10 × 10 m2) at the rates of 0 (control), 100, 200, and 300 Mg ha−1 at the Niah site and 0, 20, and 100 Mg ha−1 at the Bakam site. At the Niah site, the levels of total C and N of the soils did not change throughout the experiment in spite of enhanced soil respiration until 2 months after burning. Although burning induced an increase in the amount of NH4-N of the soils, the readily available pool of N (the sum of the NH4-N, NO3-N, microbial biomass N, and extractable organic N pools) in the burned plots was depleted appreciably at the end of rice cultivation. The effects of burning on these properties tended to be substantial with increasing amounts of the vegetation biomass burned. On the other hand, the levels of total C and N and the readily available...

Experimental shifting cultivation was conducted at the Balai Ringin (B. Ringin) and Sabal sites in Sarawak, Malaysia. At the sites, plots (10 x 10 m2) were burned with the fuel of aboveground biomass amounting to 0 (control), 100, 200, and 300 Mg ha-1. At the B. Ringin site, the soils were clayey and strongly weathered with a strongly acidic characteristic. Ash addition enabled to alleviate the soil acidity and to increase the amounts of nutrients of the soils, especially the surface soils. It was indicated that 1) N addition from ash to the soils was negligible, 2) the losses of nutrients by runoff water were not substantial compared with the amounts of nutrients contained in ash, 3) ash alkalinity seemed to be consumed for inactivating exchangeable AI mainly in the surface soils, and 4) development of variable negative charges could contribute to the retention of inorganic bases derived from ash. After harvest of upland rice, the soil chemical properties in the plots treated with 100 and 200 Mg...

Experimental shifting cultivation was conducted at two sites, Balai Ringin (B. Ringin) and Sabal in Sarawak, Malaysia. The soils at the B. Ringin site were clayey with strongly acidic nature while those at the Sabal site were sandy with a very low nutrient status. The plots (10 x 10 m2) were burned with vegetation biomass (fuel) amounting to 0 (control), 100,200, and 300 Mg ha-1 for the cultivation of upland rice. At both sites, the fire severity was found to range from moderate to high for the treatments with 200 and 300 Mg ha-1 fuel, and from low to moderate for the treatment with 100 Mg ha-1 fuel. At the B. Ringin site, the content of total C (T-C) of the soils decreased during rice cultivation which could be ascribed to the rapid decomposition of soil organic matter (SOM) and the loss of SOM due to soil erosion. One year after burning, the T-C content returned to the initial level before burning, suggesting that SOM was replenished by the addition of fresh organic matter derived from rice str...

The effects of steam sterilization (SS) on soil microbial properties including metabolic diversity of the microbial communities were examined in a greenhouse compared with those of two fumigants, methyl bromide (MB) and chloropicrin (CP). The numbers of fungi decreased in all the treatments. Nitrifiers, both ammonium-oxidizing bacteria and nitrite-oxidizing bacteria, were severely affected by the SS and CP treatments, resulting in their virtual disappearance. The decrease in the levels of microbial biomass C and N after the treatments suggested that the SS and CP treatments eradicated the microorganisms more effectively than the MB treatment and that the influence of the former persisted until the end of the experiment, 4 months after the treatments. Accumulation of NH4-N was observed after the SS and CP treatments mainly due to the partial decomposition of the dead microorganisms and the marked decrease in the number of ammonium-oxidizing bacteria. The richness and average well color development...

In spite of the significant increase in the frequency and extent of fire occurrence in Indonesia recently, little information is available about the immediate, short-term, and long-term effects of fire on soils. To investigate the effects of wildfires on the dynamics of T-C, T-N, available P, pH, exchangeable bases, and cation exchange capacity (CEC) of Ultisols from South Sumatra Indonesia, surface soils of an unburnt 9-year old Acacia mangium plantation and of A. mangium plantations burnt in 1995, 1997, 1998, and 2000 were sampled in triplicate consecutively from December 1998 until December 2000. The values of T-C, T-N, available P, pH, and exchangeable bases significantly increased immediately after the fire while the levels of Al saturation and CEC significantly decreased. Soil nutrients were still accumulated 1 year after the fire but by the end of the second year, they were depleted and returned to the pre-fire levels. Although fallowing aggraded the burnt sites, the nutrient levels in the...

In the traditional shifting cultivation system practiced by the Karen people in northern Thailand, the effects of burning on the content of extractable organic matter, microbial biomass, and N mineralization process of the soils were studied. Five plots (5×5 m2 quadrat) with 0, 10, 20, 50, and 100 Mg ha-1 of slashed materials were arranged and burned. Ten to 20 Mg ha-1 of slashed biomass corresponded to the amount commonly burned by the Karen people. During the burning process, the soil temperature at the depth of 2.5 cm in the 100 Mg ha-1 plot almost evenly increased to 300°C while the temperature in the 10 to 50 Mg ha-1 plots increased with large variations from 50 to 300°C. Burning caused a conspicuous increase in the contents of organic C and (organic + mineral)-N extracted at room temperature and a simultaneous decrease in the contents of microbial biomass C and N, especially in the soil of the 100 Mg ha-1 plot. In the rainy season, the values of the changes induced by burning reverted to th...

In order to analyze the N mineralization process under shifting cultivation in northern Thailand, labile pools of soil organic matter were studied, which were considered to be the factors contributing to the N mineralization process. Organic C, (organic + NH4 +)-N, and hexose-C were extracted from fresh soils in the surface 0–5 cm layers with a 0.5 M K2S0. solution at 110°C in an autoclave (fraction A) or at room temperature with a reciprocal shaker (fraction B), and analyzed as labile pools of organic matter. In the traditional shifting cultivation system, the content of organic C in fraction A in the fallow fields for 8 to 15 y was 3,710 mg kg-1 while that in the fallow fields for 1 y and 3 to 5 y was 2,640 and 2,600 mg kg-1, respectively. A high correlation was observed between the contents of the labile pool in fraction A and total soil organic matter. The ratio of the pool in fraction A to total soil organic matter apparently remained constant through the input-output balance in the pool. Th...

N mineralization process (ammonification plus nitrification) in the surface 0-5 cm soil layers under shifting cultivation in northern Thailand was studied. Labile pool of organic matter extracted with a K2S04 solution at 1l0°C in an autoclave (fraction A) or by shaking at room temperature (fraction B) was used as factor to evaluate the N mineralization process which was examined in an incubation experiment. In the soils, in which the N mineralization pattern was fitted to a first order kinetics model, the content of (organic + NH4 +)-N in fraction B determined the initial rate of N mineralization. The soils, which showed a short lag time of less than 7 d both in the N mineralization and nitrification processes, had a high ratio of organic C to (organic + NH4 +)-N in fraction B, exceeding the value of 7. The soils, which showed a long lag time of more than 7 d only in the nitrification process, had a low pH(KCI) (less than 4.2). Thus, the rate of N mineralization was affected by the labile pool in...

Recently agricultural activity in the mountainous area of northern Thailand has increased and problems relating to soil fertility have arisen. In order to gain basic information about the soil properties associated with shifting cultivation, physicochemical properties of the surface soils (0–10 cm) and subsoils (30–40 cm) were investigated in selected villages in the area. The physicochemical properties of the soils studied are summarized as follows: 1) The soils were rich in organic matter, content of which ranged from 11.4 to 63.3 g C kg−1 in the surface soil. 2) The pH(H2O) of the soils mostly ranged from 5 to 7 and soil acidity was more pronounced in the deeper horizons. In the surface soils, exchangeable Ca and Mg were generally dominant, whereas exchangeable Al was often predominant in the subsoils. 3) Most of the soils showed a medium to fine texture with more than 30% clay. The clay mineral composition was characterized by various degrees of mixture of kaolin minerals and clay mica with, ...

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...

This study assessed pesticide residues in soils, sediments, and vegetables in the Xuan Khe and Hop Ly communes located along the Chau Giang River in the Red River Delta, northern Vietnam. Samples were collected from agricultural areas within and outside of embankments built to prevent flooding. In Xuan Khe, the soils outside of the embankment were more clayey with higher organic matter contents compared with the inside, due to selective deposition during river flooding. Many of the soils contained significant amounts of pesticides including dichlorodiphenyltrichloroethane (DDT), dicofol, isoprothiolane, and metalaxyl although their levels were below the maximum allowable concentration set by the Vietnamese government. The spectrum of DDT derivatives found suggested that the source of DDTs was not contaminated dicofol. Soils in Hop Ly resembled soils in Xuan Khe but were relatively sandy; one field showed appreciable contents of DDT derivatives. The ratios of (p,p(')-dichlorodiphenyldichloroethylene + p,p(')-dichlorodiphenyldichloroethane)/ summation operatorDDT in the surface and subsurface soils in Hop Ly were 0.34 and 0.57, suggesting that the DDTs originated from recent application. Pesticide residues in soils were not likely to translocate into vegetable crops, except for metalaxyl. High concentrations of cypermethrins in kohlrabi leaves could be ascribed to foliar deposition.

In order to provide appropriate soil information for the rehabilitation of tropical rainforest ecosystems, we examined the soil morphological, physico-chemical, mineralogical properties and charge characteristics in a degraded mixed dipterocarp forest with three type of vegetation, namely grassland, secondary forest, and remnant forest in Japan Sarawak Friendship Forest, Sarawak, Malaysia. We compared the soil properties at six representative locations differing in topography and vegetation types, with special reference to the effect of anthropogenic activities on the catenary sequence. All the soils were acidic or weakly acidic. Contents of clay, exchangeable Al, Alo, Ald and Fed and the values of the cation exchange capacity and Al saturation increased with depth. The clay mineral composition was dominated by kaolin minerals. The value of point of zero salt effect ranged from 3.0 to 4.0, indicating that the soil was not yet strongly weathered. A catenary sequence of the soils was observed; softer in soi...