Maintenance of soybean yield with reduced phosphorus application by previous cropping with mycorrhizal plants

Previous cultivation of arbuscular mycorrhizal (AM)-host plants promotes AM colonization, phosphorus (P) uptake and the growth of succeeding AM-host plants. Three field experiments were conducted to investigate whether reduced application rates of P fertilizer could maintain soybean (Glycine max (L.) Merr. cv. Tsurumusume) yields when fields were previously cropped with AM-host plants. In the experiments, soybean was cropped after growing both AM-host (wheat, sunflower, vetch, maize and azuki bean) and non-AM-host plants (radish, white mustard, sugar beet and buckwheat) or fallow with different rates of P fertilizer (0-200 kg P2O5 ha-1). The results showed that previous cropping with AM-host plants increased AM colonization of soybean roots, soybean growth, shoot P content and yield compared with either previous cropping with a non-AM host or fallow treatment. Soybean yields following AM-host plants did not decrease with reductions in the P application rate from 150 to 50 kg P2O5 ha-1, although soybean yields decreased in some cases after non-AM-host plants or fallow treatment. A general linear model analysis revealed that soybean yield following AM-host plants was less affected by a reduction in P application rate than plants following non-AM-host plants. As a result, P application rates can be reduced from 150 kg P2O5 ha-1 (the rate recommended by the Hokkaido Government) to 50 kg P2O5 ha-1 for soybean cultivation in soils after AM-host plants.