Limited effect of mycorrhizal inoculation depending on soil type and fertilization level in a central European field trial

Recent trends indicate a substantial increase in the application of mycorrhizal inoculants (Myc) across Central Europe. These inoculants are projected to contribute to a reduction in fertilizer dependency and to facilitate the mobilization of soil nutrients. Nevertheless, most studies are conducted in tropical or arid regions with very few data on wether mycorrhizal inoculants affect soil biological activity and cereal growth in temperate climates. A 4-year field trial was set up to assess the effects of Myc treatments (Funneliformis, Clariodeoglomus, Rhizophagus)on two different soil types. Myc was applied in combination with conventional fertilization in the first three years (sowing corn-wheat-corn) and substantially reduced fertilizer application in the fourth year (sowing corn). Weather conditions and fertilizer application rates had the highest impact on crop yields and shoot biomass throughout the four-year period. Mycorrhizal inoculants consistently caused significantly greater root colonization than the control each year, regardless of the fertilization rate. Myc also enhanced root capacity, phosphatase enzyme activity, and yield, but these benefits were most pronounced when combined with reduced fertilization and Luvisol with nutrient deficiency. In contrast, higher levels of soil organic matter and microbial activity in Gleysol led to a greater yield and diminished the impact of Myc compared to Luvisol. In this experiment, the Myc’s capacity to increase yield was not enough to compensate for the yield decrease caused by reduced fertilization. Our results indicate how critical soil types and fertilizer application rates are in determining the effectiveness of Myc in Central European cereal production.