Effects of Cropping System Management On Arbuscular Mycorrhizal Fungi.

Maintaining good host plants for arbuscular mycorrhizal (AM) fungi and minimizing tillage in cropping systems can be quite important because having active AM fungal hyphae present in the soil can allow for rapid seedling colonization, better early plant growth and nutrient uptake, and improvements to soil structure. In the Sustainable Dairy Cropping Systems project (DCS) at Pennsylvania State University, we evaluated the effects of preceding crop type and system management on AM fungi. Two diverse 6-year cropping systems were evaluated that include a variety of mycorrhizal host crops and a non-mycorrhizal crop, canola (Brassica napus L.). Although the cropping systems are managed as no-till, in one of the cropping systems we use one tillage event in a six-year rotation to kill alfalfa (Medicago sativa L.) and reduce herbicide use. In these diverse systems, we evaluated the effect of the preceding winter crop on mycorrhizal colonization, seedling aboveground biomass, and %N and %P of aboveground plant tissue on corn (Zea mays L.) seedlings. We also assessed whether planting oats (Avena sativa L.) as a nurse-crop with winter canola helped sustain mycorrhizae and how one tillage event impacted AM fungi. Preceding winter crop significantly affected AM fungi, with corn seedlings after alfalfa or red clover having higher % AM colonization, biomass, and %P than corn seedlings following rye or no cover crop. Planting oats with canola did not help sustain mycorrhizae, while plowing before planting canola reduced mycorrhizal colonization of corn trap plants by 44% and seedling biomass by 21% compared to the no-tillage treatment, with the effects no longer apparent in the subsequent soybean crop.  Planning crop rotations to include mycorrhizal hosts and minimizing, but not necessarily eliminating tillage, appear good strategies to maintain AM fungi in agroecosystems.