Cassava is frequently damaged with a water-logging during rainy season in a sloping field of Northeast Thailand. The degree of damages depends on the topographic condition and soil profile morphology. Pie-zometers and tensiometers were installed to measure the water table levels and a tracer experiment was conducted to determine the soil water flow in a sloping field. We found the followings after analysing a three-dimensional subsurface soil water flow. After a rain water infiltrated into the soil layer and reached to the groundwater zone with the vertical flow, the watertable level came up and the groundwater flowed laterally along the down slope in the permeable sand layer. Whereas the watertable level fell rapidly at the upper points of the slope after rainfall had stopped, it lowered slowly at valley slopes where the groundwater concentrated or was retained. At that place the cassava root rot was caused with increasing watertable level less than 30 cm depth from the surface.
Alfisols and Vertisols are major soil types in the Indian Semi-Arid Tropics (SAT). An unstable crop production in the Indian SAT caused by the undependable rainfall is quite often aggravated by the poor physical conditions of these soils, such as poor soil aeration, crust formation, low infiltration rate etc. Pigeonpea grown on Alfisols was confirmed to develope deep root systems and to improve soil phys-ical conditions, such as infiltration rate, aeration etc., in an Alfisol field at ICRISAT (International Crops Research Institute for the Semi-Arid Tropics) Center. As a result of these improvements, sorghum grain yield in the same field was increased after the cultivation of pigeonpea under an adequate fertilizer management. Residual effect of chickpea was found to improve grain production of subsequent pigeonpea in a Vertisol field at ICRISAT Center. As an adequate amount of fertilizer was applied in this field, the beneficial effect of chickpea could be ascribed to improvement of soil physical conditions. However, this possible effect awaits quantification. In an intercropping system, pigeonpea also improved the grain yield of the associated sorghum. Planting crops on ridges also increased grain yields of sorghum and pigeonpea in both Alfisol and Vertisol fields. These increases of yield were attributed to the enhanced root development through the improvement of soil physical coditions especially soil aeration. Traditional cropping systems of the Indian SAT are found to maintain the crop productivity under low input conditions through the utilization of those legumes. Many suggestions could be drawn out from them for the development of the technology suitable for the SAT and the ecologically healthy crop production system for developed countries.
Okinawa prefecture is located in the monsoon region of Asia and has a humid subtropical climate. Therefore the properties of the soil in this district reflect the climatic factors. One particular kind of soil, called Kunigami Maji because of the locality and the local dialect, is distributed mainly in the northern parts of Okinawa island, Ishigaki island, and Iriomote island. Kunigami Maji soil in red-yellow in color and is regarded as a problem soil from the point of view of erosion. This study was made in order to estimate and to establish controling soil erosion on reclaimed fields in the northern parts of Okinawa island. The relations among the factors of USLE (Universal Soil Loss Equation) were analized on the basis on rainfall energy and soil loss from the fields. The method of analiysis adopted in the current study is indicated with reference cited. The results obtained from the investigation are summerized as follows:
1) According to 9 samples obtained from the field plots tested, K value of USLE factors is higher in silty soil than in clayey soil in each plot of inclination of 3° 5° 8°
2) R value changes from 438 (m2 tonf/ha • hr.) to 1073( m2 tonf/ha . hr.) by the year test was conducted.
3) C value of pineapple was estimatled at 0.56
4) Countermeasures against soil erosion and areas for further study were proposed as follows:
(1) The field lot like puddy is recomended to protect soil loss from ruclaimed area.
(2) Mulching with layers of grass or leaves to decrease rainfall enery and runoff.
(3) Stabilization of soil particle by using compost or humus.
(4) Reasonable layout of terrace and drainage channel.
(5) Decreasing muddiness of runoff to minimize river and ocean contamination.
This report is done from the information of the Basic Study for Agricultural Development in the Niger River Bassin done by J ALDA (Japan Agricultural Land Development Agency). J ALDA has studied the factors of the causes, and the actual stage of desertification and the control of it in the basin of Niger River from 1985 to 1990. The main purpose of it is to seek for the possibility of agriculture development in that area. We thought that the desertification control is synonym to keep environment of life. The occupants of that environment are farmers and nomadas, so the point of the desertification control is to find out how to continue modern and traditional farming system and stable grazing. In that area, the desertification doesn’t constantly make progress from the Sahara desert to the south. We can observe the vegetation recover according to the precipitation fluctuation. The intense desertification can be observed near by city side because of the population growing and the culture zones where the precipitation is about 500 mm. JALDA proposed the concepts of desertification control as the result of the study as follows.
(1)Improving the high potential area for the agriculture and social-economic condition.
(3)Connecting this high potential area with the development of the rural roads, the waterway and forest (trees and bushes).
(4)Construction of green defense zone at the northern boundary areas of culture to prevent the southward desertification.
(5)Protection forests in the water resource area and the tropica) rainy zone.
The typical topography in that area is a vast combination of the upland plain and alluvial lowland areas. In the vast land, the soil and water condition are different from each points. The vegetation makes typical ecological patterns, and there are many kind of cultivations according to the different nat-ural conditions. Considering the different condition and ecology, we have to prepare many kind of mothod of deserti-fication control, and the possibility in agriculture development and stabilizing vegetation are many also.
Coastal swamp areas are the object of reclamation for agricultural and aquacultural development in southeast Asia. First, reasons for an extraordinarily wide distribution of mangroves and swamp forests in insular southeast Asia were considered in terms of climate, vegetation, geology, geomorphology and geo-history. Then the problems expected to arise from reclamation of these swamp lands were considered. The pres-ent and past mangrove swamps, the latter being broad depressions engulfed in a delta proper due to rapid sedimentation along the delta front, are often associated with pyritic sediments which, upon drainage and reclamation, rapidly develop into acid sulfate soils. The difficulty of their amelioration was discussed. Swamp forests in the tropics are developed on woody peats that are sometimes more than 10m thick and extremely oligotrophic. Reclamation of swamp forest lands inevitably accompanies drainage, which in turn leads to land subsidence due to dewatering and compaction, and eventually to decomposition of peat itself. Results of a recent study concerning the changes brought about by peat land reclamation were presented concerning oligotrophy, peat decomposition and land subsidence. Sterility of rice on peat was also dealt with based on experimental results.
Soil salinity is one of the serious constraints for crop production in Northeast Thailand, where variously salt-affected soils estimated to be approximately 17% of the Northeast are present. However, an additional 18% of the region may be salinized without any proper countermeasures. Source of salt is red siltstone and sandstone, i.e., the upper clastic member of the Mahasarakham Forma-tion in the Northeast. There are the natural and the artificial causes of salinization. However, not the nat-ural causes associated with the geological and topographical factors, but the artificial causes by various human activities have enhanced salinization in recent years. In the present study, salt-accumulation on sandy surface soils after the clearance of the native vegetation in Phra Yun, Khon Kaen was investigated in order to clarify the process of salinization and to identify meth-ods of control. Deforestation changes the balance between rainfall and evapotranspiration, resulting in the increase of percolation and seepage water. Saline seepage water induces salinization in the footslopes and the low-lying lands. Salt-affected soils displayed mottlings in the upper part of the profile in connection with the elevation of the groundwater table in the rainy season. In these soils, salt reached the surface through the upward move-ment of saline water consisted mainly of NaCl, at the beginning of the dry season. Salt could also be easily leached out to the subsoil with rainwater in the rainy season. Accumulation of salt on the soil surface in the dry season was associated with the elevation of the ground-water table to a critical level higher than 70cm from the surface at the end of the rainy season and the con-tinuity of capillary pores above the groundwater level. To control salt-accumulation, the planting of eucalyptus trees which led to the drying of the soils and the lowering of the groundwater table was found to be effective in interrupting capillary rise of saline water and in preventing saline seepage water from reaching the low-lying lands. The low-input technology of re-forestation with eucalyptus trees can be hopeful of controlling soil salinization in the other countries.