Soil Properties and Not Crop Rotation With Non‐Mycorrhizal Canola Influence the Abundance of Arbuscular Mycorrhizal Fungi in Wheat Soils

ABSTRACT Arbuscular mycorrhizal fungi are gaining prominence in agriculture because of their role in enhancing crop nutrient uptake and stress tolerance. Soil management practices, however, may pose a non‐optimal environment for arbuscular mycorrhizal (AM) fungal functioning. The impact of crop rotation and soil properties on arbuscular mycorrhizal fungi in wheat soils was therefore investigated. Soil samples were collected from two sites where wheat was grown after wheat or in rotation with canola or medic and assessed for spore densities, root colonisation, and the concentration of glomalin‐related soil protein (GRSP). Analyses for correlations between AM fungal parameters, soil properties and wheat grain yield were conducted. Our results showed that soil properties significantly influenced AM fungal abundance while the effect of crop rotation was marginal. Wheat root colonisation increased in response to a decrease in soil phosphorus availability with a concomitant increase in available nitrogen, from 21% to 55.8% at Tygerhoek, highlighting the importance of the soil N/P ratio on AM fungal colonisation. On the contrary, spore densities increased in response to increasing soil available phosphorus levels, suggesting that sporulation may be an AM fungal strategy for surviving adverse conditions. They fluctuated from 32.3 to 204 and finally 86.1 per 50 g soil at Tygerhoek and from 163 to 166 and finally 69.4 per 50 g soil at Langgewens due to seasonal fluctuations in soil available phosphorus. The concentration of GRSP was shown to be positively correlated with soil fertility indicators such as percent carbon and β‐glucosidase and wheat grain yield ( p < 0.05), confirming the role of AM fungi in enhancing soil fertility and consequently yield. Our findings contribute to the understanding of the effects of soil management practices on AM fungi, which provide important agricultural services.