Land-use and soil-quality dynamics in an agricultural area of Nakhon Ratchasima province, Northeast Thailand | |
| Author | Khin Mar Cho |
| Call Number | AIT Diss. no.AS-03-02 |
| Subject(s) | Land use--Thailand--Nakhon Ratchasima Soils--Thailand--Nakhon Ratchasima--Quality |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. AS-03-02 |
| Abstract | The study addresses the interrelationships between land-use successions and soil-quality in a typical rainfed agricultural area of Nakhon Ratchasima Province, northeastern Thailand. The two main aims of the study were (i) to characterize typical land-use types in the area in the context of their history and the driving forces behind land-use changes, and (ii) to assess the soil-quality differences that can be associated with these land uses. For the first part of the study, the typical land-use successions were identified through detailed land-use history profiles based on interviews and discussions with the farmers in the area. The second part comprises detailed soil characterization for selected land uses and the development of a compound soil quality index (SQI) that can be used to detect overall changes in soil quality between the different types of land use in the area, including undisturbed forest Land-use successions: From the 1960s onward, people started to settle in the area and began to clear-cut the forest to grow subsistence crops, such as upland rice and castor beans. After a relatively short period dominated by subsistence crops, the land use rapidly developed into maize-based cash-crop systems. Maize is still the main crop. Since the beginning of agriculture in the area, the farmers practiced continuous cropping. Shifting cultivation was never practiced. Initially, the soil was not tilled, and dibbling of seeds was exclusively practiced. All soil and crop husbandry practices were carried out manually. Due to the influx of more people, the agricultural land area expanded rapidly. Six typical land-use successions, from the initial forest clearing to the present land¬-use, have been identified, i.e., (i) Forest —> maize-maize (2 crops per year) rotation (ii) Forest —> maize-fallow (1 crop per year) rotation (iii) Forest —> maize-maize —> mungbean-maize rotation (iv) Forest —> maize-maize —> orchard (v) Forest —> maize-maize -> orchard maize-maize and (vi) Forest —> maize-maize —> orchard —> vegetables. With the change of the land-use systems over time, the agronomic practices also changed adapting to the requirements of the new crops. The application of inorganic fertilizers, herbicides and pesticides became standard practice. The use of these inputs led to a significant increase in land productivity. However, most farmers do not have sufficient capital to purchase all required inputs for cultivation and they largely depend on private money lenders and middlemen for input supply at extremely high interest rates. There is a general perception amongst farmers of a considerable soil-fertility decline and that more and more fertilizer needs to be applied to maintain the current yield levels. Soil-quality changes: For a comparative assessment of soil quality, 37 sites representing 7 typical land uses (including 3 forest types) were selected for detailed investigations. At each site, the soil was characterized and samples from all soil layers (up to a depth of about 1.2 - 1.4 m) were analyzed for 20 different chemical and physical characteristics. A direct comparison of individual soil properties could not conclusively explain soil-quality differences. As expected, the forest soils generally exhibited significantly higher levels of soil organic matter and lower bulk density than the arable soils. Clay dispersion was generally high and nutrient levels were generally low, pointing to highly leached and inherently low-fertility highly erodible soils, typical for the region. The comprehensive analysis of soil quality followed a three-step approach, i.e., (i) the identification of a minimum dataset (MDS) of indicators that contains those soil properties which best represent the soil functions; (ii) scoring of the indicators according to their performance within the dataset; and (iii) integration of the indicator scores into a comparative soil-quality index (SQI). The main analytical tools used to develop the SQIs were principal components analysis, factor correlation and analysis of variance. The main soil properties (i.e., soil-quality indicators) that characterize the different land-use systems and their successions were different for the topsoil and the rooted subsoil. For the topsoil, 13 significant soil-quality indicators were identified. Most of these indicators related to the physical characteristics and the organic matter content of the soils. For the rooted subsoil, 5 indicators were found of which all were related to soil structure and organic matter content. These indicators were used for the minimum dataset to develop compound soil-quality indices (SQIs). The indices clearly showed that, overall, forest land uses maintain higher soil quality than agricultural land uses, both in the topsoil and rooted subsoil. However, not all associated SQIs were significantly different from each other. For the topsoil 4 distinctive ranks of SQI were identified for the land-use types studied (i.e., 1— secondary forest; 2— reforested land and mungbean-maize rotation; 3— maize-maize rotation and orchards; 4— maize-fallow rotation). For the rooted subsoil 3 ranks were identified (i.e., 1— secondary forest; 2— maize-fallow rotation; 3— reforested land, orchards, mungbean-maize rotation, maize-maize rotation). Soil quality -as addressed in this study- describes the essential soil conditions that set the limiting frame for long-term soil use. In the study area, the nutrient status is obviously not an indicator of soil quality as there is no nutrient build-up over time in any of the land uses. Soil quality is, however, strongly correlated with soil structure. The two decisive indicators in the SQIs, i.e., those indicators that can most clearly reveal soil¬-quality changes, are soil organic matter and aggregate strength. Therefore, approaches to maintain and enhance soil quality in the study area must be linked to better recycling of organic materials and on-farm organic matter management. To achieve sustainable soil use in the study area, land-use technologies need to be adopted at the farm level that increase the efficiency of organic matter cycling, maintain favorable soil structure and reduce soil-degradation risks. This should include the incorporation of crop residues. Rotations with legumes, such as mungbean, will produce additional easily decomposable organic matter, with the favorable side effect of nitrogen fixation. Another option to improve organic-matter management would be the integration of livestock and introduction of ‘organic farming' into the farming systems. Simultaneously, an enabling environment needs to be developed based on appropriate extension services and adequate credit facilities for the farmers. With improved land management, the decreasing trends of soil quality in the study area can probably be reversed in the long run. |
| Year | 2003 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. AS-03-02 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Aquatic Systems(AS) |
| Chairperson(s) | Zoebisch, Michael A.; |
| Examination Committee(s) | Ranamukhaarachchi, S. L.;Clemente, R.;Hurni, Huns; |
| Scholarship Donor(s) | Dr. Gunnar Kjer Hansen Memorial Scholarship Prospect-Burma;Asian Institute of Technology Joint Scholarship; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2003 |