Soils Determine Early Revegetation Establishment with and without Cover Crops in Northern Mixed Grass Prairie after Energy Development

Cover crops have been used to build soil health and improve ecosystem services in agricultural fields and pastures, but they have not been tested in restoration contexts. We conducted two experiments in interim oilfield reclamations at Ft. Berthold Indian Reservation in North Dakota: in 2014 two different perennial grass mixes, with and without an oat cover crop and, in 2015, a single grass mix with and without a cover crop cocktail. To determine whether cover crops speeded site recovery or whether they competed with perennial grasses, all sites were assessed for plant establishment and rangeland health in August 2015. Sites planted in 2014 ranged from 20 (± 10 SD) to 38 (± 0.5) perennial grass plants/m2. Sites planted in 2015 ranged from 6 (± 1.8) to 29 (± 11) plants/m2. Cover crop treatment and grass mix treatments were not significant determinants of perennial grass establishment (p > 0.05). Soil nutrients appeared to drive early revegetation establishment: sites with poor perennial grass establishment had lower levels of phosphorous and higher levels of calcium, iron and manganese. Rangeland health trended towards being greater when a cover crop was planted, but the effect was very small. We will eventually test whether the long-term benefits of cover crops in agricultural systems transfer to restoration, but when cover crops establish at low densities, as we observed in these studies, they may only have small effects in reclamations.