2012 Volume 56 Issue 1 Pages 2-12
Soil fertility under various land use types in a village in Mae Taeng District, Chiang Mai Province in northern Thailand was investigated based on soil physicochemical properties. The land use changed toposequentially with altitude; residences with home gardens, perennial cash crop orchards (lychee and orange) and teak plantations were located on relatively flat lands at the bottom of the valley, while banana stands and bamboo-mixed secondary forests were on steep slopes of the mountainsides. Remnant forests remained only around the ridges. Soils were relatively sandy in texture and were almost neutral to slightly acidic in reaction. Exchangeable cations were predominated by Ca and Mg with a low level of Al saturation. The level of available P was low. It was revealed that soil organic matter played important roles for CEC and physical properties both in the surface and subsurface layers. In terms of land use types, the levels of total C and total N were lower in the farmlands and teak plantations than in remnant forests and bamboo stands. It is indicated that the reduction in soil organic matter could not be avoided by farming practices, even under lychee orchards and teak plantations where abundant leaf litter was supplied to soil surface. The soils under bamboo and banana stands showed relatively high pH values and high contents of exchangeable bases, of which levels were similar to or even exceeded those in lychee and orange orchards with fertilizer application. This could be ascribed to repeating fire occurrence as well as the addition of nutrient rich surface soils from upper slopes. In the lychee and orange orchards, the nutrient levels at the fertilizer-applied points under the tree canopy were mostly similar to or lower than those in-between the trees, except for available P, indicating nutrients added to the soil surface seemed to be leached downward by plentiful water supply with sprinkler systems unless taken up by plants.
