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Shinya Funakawa Sota Tanaka Thammanoon Kaewkhongkha Tomoo Hattori Koyo Yonebayashi 《Soil Science and Plant Nutrition》2013,59(3):665-679
Abstract 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, in some cases, a certain amount of 2:1-2:1:1 intergrades. 4) According to the ion adsorption curves, most of the B horizon soils were characterized by the predominance of permanent negative charges. On the other hand, organic matter contributed to the increase of variable negative charges in the surface soils. The content of organic matter and the percentage of the clay fraction were essential for determining the CEC of the soils of the surface 10 and 30–40 cm depths, respectively. Under the field conditions, the composition of exchangeable cations largely reflected the soil acidity. In addition, the content of organic matter also showed a significant correlation with that of available N in the surface soils. Thus, soil acidity both in the surface soils and subsoils, organic matter content in the surface soils, and clay content in the subsoils were considered to be the main factors that affected soil chemical fertility in the area. 相似文献
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Shinya Funakawa Sota Tanaka Hitoshi Shinjyo Thammanoon Kaewkhongkha Tomoo Hattori Koyo Yonebayashi 《Soil Science and Plant Nutrition》2013,59(3):681-693
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 markedly decreased under continuous cropping. The contents of C, N, and P in the microbial biomass of the surface 10 cm layers of soil ranged from 0.37 to 2.09 mg C g?l soil, from 22.7 to 188 µg N g?l soil, and from 6.1 to 65.7 µg P g?l soil, respectively. Since the contents of microbial C, N, and P in the surface soils were generally higher under prolonged fallow and natural forests than in the fields continuously cultivated, the microbial activity and/or the amounts of C, N, and P available for biological activity seemed to have declined under continuous upland farming. The incubation experiment to assess the N mineralization pattern showed two remarkable characteristics: 1) there was an initial time lag until active mineralization of N occurred in the soils from young fallow forest and 2) the soil burning effect was observed after burning in the fields under prolonged fallow. The active process of nitrification after N mineralization was always associated with a sharp fall in soil pH, suggesting that soil acidification was promoted and basic cations were lost from the soils. In conclusion, rapid deterioration of the soil organic matter-related properties in cropping fields can be considered to be one of the ecological reasons why upland fields must be returned to fallow again a few years after forest reclamation in traditional shifting cultivation systems. Therefore, in alternative farming systems with more intensive land use, it is essential to apply organic materials into soils to decrease the rate of soil degradation, or to improve the soil fertility, in avoiding soil acidification along with nitrification. 相似文献
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Sota Tanaka Tomonori Ando Shinya Funakawa Chainarong Sukhrun Thammanoon Kaewkhongkha Katsutoshi Sakurai 《Soil Science and Plant Nutrition》2013,59(3):547-558
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 the values recorded before burning, except for the microbial biomass in the 100 Mg ha-1 plot, which still remained lower. Based on an incubation experiment, N mineralization rate was higher in the soils taken just after burning, especially in the 100 Mg ha-1 plot, than in the soils taken during the rainy season. However, the soil in the 100 Mg ha-1 plot was considered to have the lowest ability to supply mineral N among the soils in the rainy season. Burning of 10 to 20 Mg ha-1 biomass corresponding to the values recorded in Karen peoples' shifting cultivation system was more compatible with soil ecology in terms of N supply at the initial stage of crop growth and of microbial biomass recovery during the rainy season, compared to the burning of 100 Mg ha-1 biomass corresponding to the value recorded in a natural forest. Thus, the shifting cultivation system implemented by the Karen people can be considered to be a well-balanced agricultural system. 相似文献
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Sota Tanaka Shinya Funakawa Thammanoon Kaewkhongkha Tomoo Hattori Koyo Yonebayashi 《Soil Science and Plant Nutrition》2013,59(3):695-708
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, which were expected to be added to the soils with ash input, ranged from 3 to 4 kmol( + ) ha?1 or kmol(-) ha?1 , respectively. In the fields under continuous cultivation for more than 4 y after the slash and burn practice, the subsoils showed a more acidic nature than in the fields immediately after burning. Judging from the high concentrations of inorganic bases in the soil solution from the subsoils, the decrease of the content of exchangeable bases and resulting soil acidification might have proceeded through leaching loss of these bases. Among the exchangeable bases in the soils, Ca and Mg were generally predominant and K occurred as trace. Comparison of the total contents of the bases with the contents of exchangeable ones showed that most of Ca occurred in an exchangeable form while most of K and Mg occurred in the nonexchangeable forms in the soils. Therefore, Ca was likely to be readily depleted along with soil acidification in continuous cultivation. 相似文献
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Sota Tanaka Shinya Funakawa Thammanoon Kaewkhongkha Koyo Yonebayashi 《Soil Science and Plant Nutrition》2013,59(4):527-537
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. The content of the labile pool in fraction B was the highest among the fields cultivated for 1 y after the slash and burn practice and it decreased in the course of the fallow period. The content of organic C was 548 mg kg-1 in the fields cultivated for 1 y and 235 mg kg-1 in the fallow fields for 8-15 y, respectively. There was a reverse relation between the contents of the pool in fraction B and microbial biomass. Therefore, the origin of the pool in fraction B was attributed to the microbial debris associated mainly with a decrease in the soil moisture content in the dry season. On the other hand, in the relatively intensive cultivation system, there was no significant difference in the contents of the labile pools both in fractions A and B among the land use stages, suggesting that the preservation mechanism of these pools, which was observed in the traditional cultivation system, did not operate well in the intensive system. In alternative farming systems in future, it will be essential to apply organic materials to soils to supply organic matter and to maintain the microbial biomass. 相似文献
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Sota Tanaka Shinya Funakawa Thammanoon Kaewkhongka Koyo Yonebayashi 《Soil Science and Plant Nutrition》2013,59(4):539-549
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 fraction B or soil pH. On the other hand, there was a correlation between the N 0 + N max (inorganic N at 0 d + maximum amount of mineralizable N) value and the labile pool in the fraction A, suggesting that the N 0 + N max value depended on the contents of the labile pool. 相似文献
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