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Greater productivity under intercropping has been attributed to the complementary use of environmental resources. However, the rooting pattern of component species under intercropping, which is an important morphological feature considering the complementary uptake of nutrients, has been studied only rarely under field conditions because of inherent technical difficulties. We examined rooting patterns of three green manure species, both sole cropped and intercropped, using a newly developed multi-color staining technique. Species were chosen from different functional groups: sorghum (Sorghum bicolor (L.) Moench.), a C4 grass; crotalaria (Crotalaria juncea L.), a legume; and sunflower (Helianthus annuus L.), a C3 dicot. We also investigated these species' aboveground biomass and N uptake. Sorghum distributed roots deeper under intercropping than under sole cropping; it was the most important contributor to increased biomass under intercropping. Crotalaria had a deep rooting system under both sole cropping and intercropping. Sunflower, with a shallow rooting system, was suppressed extremely under intercropping, possibly because of water deficiency in late in the season. The rooting patterns of green manure species examined using multi-color staining were related closely to the aboveground performance of these species under intercropping.

To determine the taxonomic relationship between Thai soybean bradyrhizobia and soybean bradyrhizobia from other regions, a total of 62 Bradyrhizobium strains were isolated in Thailand. The genetic diversity of the strains was examined with reference to 46 Japanese and 15 USDA strains. The degree of sequence divergence in and around common nod gene regions of the 123 strains was estimated by restriction fragment length polymorphism analysis using the Bradyrhizobium japonicum USDA 110 common nodDYABC gene probe. The phylogenetic grouping of the strains resulted in four major clusters. Cluster 1 comprised the Japanese and USDA strains, which originated in temperate regions, whereas clusters 3 and 4 comprised the tropical Thai strains. Cluster 1 strains comprised the DNA homology groups I and Ia, and hence, were classified as B. japonicum. Cluster 2 strains were in the DNA homology group II, and hence, were classified as Bradyrhizobium elkanii. Clusters 3 and 4 strains, however, did not correspond to any known DNA homology groups. These results indicate that Thai soybean bradyrhizobia are distantly related to B. japonicum and B. elkanii.