© 2019While establishment and persistence of arbuscular mycorrhizal (AM) fungal inoculants in agricultural fields are critical to their success, little is known about how farming practices can affect their establishment in field. We developed a probe assay specific to a commercial AM fungal inoculant (Rhizoglomus irregulare DAOM197198) and tested its establishment among different grain cropping practices in the field. Establishment of the fungus was not related to cropping, or inoculation practices. Instead, establishment was site specific over the two growing seasons. Our results show that it is not yet possible to predict inoculation success in the field and use of biofertilizers requires further research under field conditions to identify key factors involved in establishment and persistence.