Advancing Cover Crop Knowledge: Assessing the Role of Plant Diversity on Soil Change

Project Overview

Project Type: Graduate Student
Funds awarded in 2018: $25,000.00
Projected End Date: 03/31/2020
Grant Recipient: Montana State University
Region: Western
State: Montana
Graduate Student:
Major Professor:
Dr. Perry Miller
Montana State University


  • Agronomic: wheat


  • Crop Production: cover crops, fallow, nutrient cycling, nutrient management, water management
  • Education and Training: on-farm/ranch research, participatory research
  • Natural Resources/Environment: biodiversity, soil stabilization
  • Production Systems: dryland farming
  • Soil Management: nutrient mineralization, organic matter, soil analysis, soil chemistry, soil microbiology, soil physics, soil quality/health
  • Sustainable Communities: local and regional food systems


    In low rainfall areas of the northern Great Plains, cover cropping is aimed at greening the summer fallow period. Over time, soils may improve sufficiently so that the increased crop return outweighs the cost of cover crops. This study utilized two on-farm sites (Amsterdam and Conrad, MT) that were begun in 2012 (SARE Project SW11-099)  in dryland Montana to compare different plant functional groups’ effects on soil properties. Eleven treatments were included in this replicated plot-scale study, including paired plant species representing four plant functional groups (brassicas, fibrous rooted, nitrogen fixing, and tap rooted crops) in various combinations and sole pea and chemical fallow as controls. The experimental design provides a unique opportunity to test each functional group, whereby 1) each group appears separately as four functional group treatments (‘presence’), 2) they appear together in a complete mixture, and 3) the complete mixture minus each functional group (‘absence’). Due to the semi-arid climate, biomass production is low and so more time is required to see soil differences,  highlighting the importance of this 8-year long term study. This research investigated the role of cover crops verse fallow ground, plant functional groups within cover crop mixtures, and diversity within mixtures, which all may allow for more strategic design of cover crop seed mixes for targeted soil improvement. Cover crops containing nitrogen fixers produced more biomass than mixes that didn’t contain nitrogen fixers at Amsterdam, but not consistently so at Conrad. This study found that when comparing soil that grew cover crops to bare soil (summer fallow), no differences were seen in soil enzymes or arbuscular mycorrhizal colonization after four cover crop cycles. Potentially mineralizable nitrogen (PMN) was higher in the cover crop plots (pea and full mix) than the summer fallow plot at the Amsterdam site at the medium N rate (p < 0.01). When comparing the four functional groups not many differences were seen in the biological soil parameters. Soil enzymes, PMN, and microbial biomass did not show any differences by plant functional group. Arbuscular Mycorhizal Fungi (AMF) had higher colonization rates in the wheat following the fibrous root treatment than the brassica treatment at the Conrad site, likely due to the fact that brassica’s do not make mycorrhizal associations (p < 0.01). Summer fallow had a higher wheat grain yield at Amsterdam than the full mix and the pea treatment for the medium N rate, whereas no differences were seen between the three at the Conrad site. As expected, wheat following a mix that contain nitrogen fixers tended to have higher protein content than mixes without nitrogen fixers. This research provides a strong cautionary statement about producer expectations in soil improvement with cover crops in this low rainfall, semi-arid region.

    Project objectives:

    Soil and Agronomic Objectives
    1. To investigate how biomass production compares among the ten cover crop treatments included in this study.
    2. To measure how plant functional groups affect biological, chemical, and physical soil properties, and subsequent wheat yields and protein, differently.
    Educational Implications
    3. To increase local producer knowledge of the value, or lack there-of, for cover crop mixtures compared with less diverse cover crops for biomass production, soil water and nitrogen use, and change in biological, chemical, and physical soil properties.
    4. To provide producers with information regarding the potential benefits of alternative cover crops through scientific publications, extension publications, popular press articles, social media, public presentations, and research summaries and factsheets.
    The results of this research will provide fundamental knowledge on the ability of different plant functional groups to change soil properties distinctly. This base knowledge will be helpful in optimizing strategies for deploying cover crop mixtures over time and to serve specific functions
    to the soil.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.