The role of mycorrhizae in phosphorus nutrition of maize is related to the fact that the P concentration in maize shoots at the four- to five-leaf stage affects final grain yield. In the early 1980s greater early-season shoot-P concentration (mg/g) and P absorption (mg/plant) from a no-till compared to a conventional tillage system were observed in Guelph, Ontario, Canada. Further studies established that the greater P absorption is due to a more effective arbuscular mycorrhizal (AM) symbiosis when the soil is not disturbed. The greater P absorption is largely a result of the undisrupted mycelium present in an undisturbed soil, rather than to increased colonization. This mycelium retains viability through extended periods in frozen soil. In the spring this mycelia network is able to acquire P from the soil and deliver it to the plant immediately upon becoming connected to a newly developing root system. Increased P absorption has not resulted in increased grain yield in field trials. Some additional factor limits yield with no-till maize preventing the advantage of early P absorption from being realized as yield. When maize follows a non-mycorrhizal crop such as rape, mycorrhizal colonization is delayed, reducing early-season P absorption. Yield reductions may occur.
