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Toposequence of Soils in Nakhon Ratchasima Province, Northeastern Thailand
Dissertation Abstract:
Four soil profiles in each toposequence of Amphoe Muang and Amphoe Dan Khun Thot, Nakhon Ratchasima Province were studied to determine their physical, chemical, and mineralogical characteristics and to gain understanding of the nature of their genesis in relation to the topography.
The mineral contents of the silt fraction were determined by x-ray diffraction technique. The clay was characterized using x-ray diffraction and differential thermal analysis (DTA). The mineralogy of the light and heavy minerals in fine sand and very fine sand frictions was determined by grain count using petrographic microscope. The micromorphology study was performed on thin sections from selected horizons in each profile.
The Amphoe Muang Toposequence Profile SR-4 found in the low terrace contained more clay than the other three profiles that occurred on the higher terrace or elevation. In the Amphoe Dan Khun Thot toposequence, Profile SR-8, which occurred in the same physiographic position as Profile SR-4, contained more available water than the rest of the profiles. These profiles also had more exchangeable bases, higher pH, higher cation exchange capacity, and higher electrical conductivity.
The clay mineralogy suite in Amphoe Muang toposequence contained more kaolinite in the high and middle terraces and in the upper part of the low terrace. In the Amphoe Dan Khun Thot toposequence, this clay mineral was moderate to small in amounts in the same physiographic position. In both toposequences, montmorillonite was concentrated in the low terraces.
Mineral assemblages in the profiles indicated the weathering of soils from alluvial sediments. Since the parent rocks were sandstones and siltstones, the soils are quartz-rich, with very few, if any weatherable minerals and ubiquitous heavy minerals. The few lower stability minerals found in the soils were found in the low terrace.
Soil development has resulted in a lossely-bound, clay poor, S-matrix with low degree of orientation in the upper horizons and illuvial B-horizons with more oriented plasma in the lower part of the profile. Iron and manganese oxide nodules in the lower part of some profiles were directly related to iron mobility and accumulation associated with fluctuations of the water table.
Seven of the profiles in both toposequence, which showed the evidence of argillic horizon, were classified as Ultisol and Alfisol. The Ultisols were Profiles SR-5 and SR-6, classified as Typic Paleustults, and Profile SR-2, classified as Oxic Paleustult. For the Alfisols, SR-1 was classified as Oxic Paleustalf, SR-3 as Ultic Haplustalf, SR-7 as Typic Haplustalf, and SR-4 as Aeric Tropaqual. On the other hand, Profile SR-8, which had no argillic horizon, fitted well in the Inceptisols order and classified as Aeric Tropaquept.
Characteristics of these soils indicated serious problems in their management under cultivation. The nutrient level was very deficient for most crops. With the present crops and level of management, response to fertilization and irrigation is still very poor because of other limiting soil factors.
Multiple improvements in other essential factors of publication are also needed. Improvements are taking place but sustained efforts on all aspects of the problem are required for effective and lasting progress. Understanding of the soil resources and their management requirements are essential to these developments.