meters (Limpinuntana, 2001). The climate of Northeast Thailand
as classified according to Köppen is tropical savanna. The mean
annual rainfall, mean maximum temperature, and mean annual
pan evaporation in the region are 1183 mm, 32.5 °C, and
1862 mm respectively (Noble et al., 2000a).
The soil on which the study was conducted was classified as an
isohyperthermic Oxic Paleustults (Soil Survey Staff, 1992).
Selected soil physical and chemical properties of the trial site prior
to the implementation of treatments are presented in Table 1.
Before the establishment of the study the area had been under
regenerated native grass species that was used for grazing and
contained a mixture of grass and legume species. Over the past
20 years the site had been used to grow upland crops (i.e. maize)
and the production of Stylosanthes and other forage grass species
for seed and fodder production.