Abstract
The introduction of barley as a winter cover crop (WCC) provides increased yield of no-till soybean. In this cropping system, barley is mowed at the grain-filling stage before soybean cropping, and we speculate that WCC increased the yield of soybean by increasing nutrient uptake including the promotion of phosphorus uptake by improving arbuscular mycorrhizal (AM) colonization. Most of the previous reports on the growth promoting effect of AM fungi are restricted to the growth in the early stage. In this study, the effects of AM fungi on the growth, phosphorus uptake, and nodule formation of no-till soybean in ripening stage were examined. Field survey was conducted in two fields: the first year soybean cropping with and without WCC (1YSF) and the third year of continuous soybean cropping with and without WCC (3YSF) in 2008. The results showed that the yield of soybean with WCC was higher than that without WCC in 1YSF, but not in 3YSF. The rate of AM colonization was increased by WCC in both fields. The leaf color values were increased by WCC in 1YSF, but not in 3YSF. The nodule weight tended to be increased by WCC in both fields. We considered that WCC contributed to survival of AM fungi, which promoted P uptake and extended nodulation period leading to increased yields in 1YSF. In 3YSF, however, WCC failed to increase yield because the yield was limited by nitrogen.
