Abstract
No-tillage soybean culture using winter barley as a cover crop was developed to control annual summer weeds and reduce labor. With this cover crop system, the soybean yield is higher than with a non-cover crop system, although the mechanism is not clear. One factor of the mechanism is suggested to be the nitrogenous supply from barley residual. This research examined the relationship between the arbuscular mycorrhizal (AM) colonization of barley and soybean. The AM colonization of soybean became greater with the cover crop system. The root length density and the AM colonization of barley became greater when the barley was sown earlier. The AM colonization of deep roots was greater than that of shallow roots. As the barley sowing time became earlier, the AM-colonized root length density of barley, which was derived by multiplying the root length density by the AM colonization rate, became greater. There was a significant correlation between the AM colonization of soybean and the AM-colonized root length of barley at a depth of 0—20 cm. These results suggest that the AM fungi at a depth of 0—20 cm affect the AM colonization of soybean acting as AM fungi inocula.
