Field Observations of Soil Moisture, Suction and Movement of Cornfield in Tropical Highland with and Without Vetiver System

An increasing large number of cornfield have been cultivated in highland of many Southeast Asian countries. In most cases, this corn plantation is done without proper soil & water conservation such as vetiver system (VS), thus causing land degradation and shallow slide. This study is aimed at investigating the field behaviour of slopes with corn plantation with and without vetiver system in Chiang Mai, Northern Thailand. Tensiometers, soil moisture sensors, in-place inclinometers and tiltmeters were installed at a slope in two locations, with and without vetiver system from surface to 2m depth. The monitoring results show that for the vetiver treatment, the soil moisture tended to be higher and response faster to rainfall than the cornfield without vetiver. However, the pore-water pressure in the root zone (about 0.5m) was higher for the vetiver treatment than the cornfield which only has the root depth of about 0.2m. For cornfield without vetiver, the seasonal variation of the soil moisture and pore-water pressure was also larger. Tiltmeter indicates a larger surface movement in the cornfield without VS. However, the inclinometer readings suggested that for slope with VS there was some cyclic movement toward hillside at the surface. This could be an indication of non-uniform settlement of soil layers or influence of groundwater rising.