PS 34-249 - Can management of crested wheatgrass (Agropyron cristatum (L.) Gaertn.) be assisted by restoring soil health?

Abstract: United States land managers seek to restore diversity of native plant species to areas dominated by crested wheatgrass (CWG) (Agropyron cristatum (L.) Gaertn) but have had limited success. CWG is a perennial bunchgrass was introduced from central Asia during the drought of the 1930’s for its abilities to establish easily, stabilize soil, tolerate drought and frost, and provide livestock forage. These competitive abilities have made CWG one of the most widespread invasive species in the Great Plains and western North American rangelands; being planted somewhere within 6-10 million hectares. CWG soils have been shown to have poor physical-chemical properties, lower total microbial abundance, and lack of molecular signatures for arbuscular mycorrhizal (AM) fungi, which more than 80% of plant species depend on for essential soil nutrients.

This study was initiated by the Bureau of Land Management (BLM) and serves to understand the impact of CWG management methods on soil physical, chemical, and biological properties in order to find the most effective treatment method for reducing CWG cover and enhancing soil for native species establishment. The field studies were modeled after the BLM’s assessment inventory monitoring protocol, which provides unbiased vegetation monitoring through data collection along a 25 m transect line. Each treatment had 12 vegetation transects with data collection every 5 centimeters. The field study was conducted in May through September of 2022 in the Northern Great Plains region of the United States near Glasgow, MT and represents vegetation during and after the summer growing season.

The CWG management methods analyzed, both alone and in combination, were: control (no treatment), herbicide, tillage, cover crops, and a biological soil amendment. From our first vegetation study, we found that the lowest to highest percentages of CWG cover are as follows: Cover crop + Amendment + Tillage + Herbicide 7.03% ( ±0.03), Cover crop + Amendment + Tillage 8.52% (±0.05), Cover crop + Tillage 9.60% (±0.04), Cover crop + Herbicide 11.09% (±0.09), Herbicide 14.73% (±0.09), Amendment + Herbicide 18.37% (±0.08), Control 23.46% (±0.08), Amendment 30.45 % (±0.13), Cover crop 32.17% (±0.11), Cover crop + Amendment 35.49% (±0.12). The field study treatments will be repeated in 2023 and supplemented with a greenhouse study and soil analyses. We expect that conditioning the soil to promote microbial activity will aid in future grassland restoration efforts.