Mutualistic functioning of indigenous arbuscular mycorrhizae in spring barley and winter wheat after cessation of long-term phosphate fertilization

 The influence of 23 years of phosphorus (P) application at three annual rates of 0, 17.5 and 52.5 kg ha–1 on arbuscular mycorrhizal (AM) fungal colonization was studied 10 years after the fertilization treatment ended. The annual application of 52.5 kg ha–1 was about twice the annual crop P extraction and after 23 years had resulted in a measured increase of 23% in the soil total-P concentration. After 10 and 11 years without fertilization, the total mycorrhizal and arbuscular colonization of the plots previously fertilized at this high rate were still significantly lower than in the plots subjected to the 0 and 17.5 kg ha–1 rates. Plots previously fertilized annually at the rate of 52.5 kg ha–1 also had a lower benefit : cost ratio for the symbiosis between AM fungi and plants. Furthermore, P-use efficiency was lower in these plots, although no decrease in total dry matter production was found.