Assessing and solving nutrient deficiencies in the highlands
1996
Niwat Hiranburana (Chiang Mai Univ. (Thailand). Faculty of Agriculture. Dept. of Soil Science and Conservation)
Nature and magnitude of crop production is determined by the soil and water regime in a specific environmental system. Soil and water management complement and supplement the ecological capabilities to maximise and sustain agricultural production. Thus, an understanding of the potentials of the natural resources (soils) and of their interaction under the various agro-ecological designs is a prerequisite for utilization of these resources. Highland soils which cover about 70 percent of the Northern area of Thailand, are extremely complex and diverse. Forest destruction by the hilltribes has impaired the country in terms of ecosystem and economy as well. It has detrimental effects on water supplies and qualities including flooding, which are due to shallowness of rivers and reservoirs as a result of sedimentation. In general, the organic matter contents of highland soils are in the range of 3.5-5.0 percent in the surface soils. Soils are acid with a pH of 5.3-5.6 and tend to be phosphorus and sulfur deficient. Phosphorus and sulfur in the surface soils are between 10-15 ppm and 15-20 ppm, respectively. These highland soils contain a high content of extractable potassium which is above 200 ppm in the top soils, whereas magnesium supplements are needed for certain crops because of its low content (0.7-0.9 me/100 g). Zinc and boron deficiencies are commonly observed in the highland areas which are covered with several kinds of crops such as coffee, fruit trees, vegetables and various flower crops. Toxicity of manganese is considered a possibility to plants since it is found at the level from 13-17 ppm by NH4OAc extraction.
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