Chiang Mai Journal of Science

Mimosa invisa weed which is used as green manure for increasing soil fertility and organic matter. They arecolonized by arbuscular mycorrhizal (AM) fungi which increase nutrient uptake by the plant. In addition, roots ofatmosphere. The objectives of this research are (1) to study diversity of AM fungi in is widely distributed in Northern Thailand. M. invisa is a leguminousM. invisa are nodulated with Rhizobium bacteria that fix N2 from theM. invisa in cultivated, uncultivated and seasonally wet areas in Chiang Mai province (2) to evaluate the effect of soil pH (4.0, 5.0 and 6.0) on AM spore production in two varieties of M. invisa (thornless and thorny mimosa) and (3) the effect of AM fungi on the host plant in a pot experiment. Twenty-three species of AM fungi were found in the root zones of the study areas. The highest spore density occurred in uncultivated areas, slightly lower in cultivated areas and lowest in seasonally wet areas. In the pot experiment, AM fungi significantly increased dry weight, nutrient contents (N, P and K) in shoot, root and N in nodule in all treatments. The soil pH had effect on root colonization and spore density. The optimal soil pH for root colonization and spore production of AM fungi was pH 5.0 associated with both varieties of soil pH 5.0 was 88% and 80%, respectively. The highest spore density in soil pH 5.0 of thornless mimosa was 16.3 spores g mimosa had root colonization and spore density of AM fungi higher than thorny mimosa. Therefore, in addition to the ease in handling without the sharp little thorns, the thornless mimosa is more suitable for using as green manure and as natural inoculum of AM fungi in agriculture than thorny mimosa. M. invisa inM. invisa. Root colonization in thornless mimosa and thorny mimosa in the-1 soil while thorny mimosa was 7.3 spores g-1 soil. Thornless