Using cover crop mixtures to improve soil health in low rainfall areas of the northern plains

2013 Annual Report for SW11-099

Project Type: Research and Education
Funds awarded in 2011: $354,405.00
Projected End Date: 12/31/2015
Region: Western
State: Montana
Principal Investigator:
Dr. Perry Miller
Montana State University

Using cover crop mixtures to improve soil health in low rainfall areas of the northern plains


We test effects of cover crop mixtures (CCMs) grown during the summer fallow period on soil biological, chemical and physical parameters, and wheat yield. CCMs include plant functional groups that 1) fix N, 2) provide ground cover, 3) have deep tap roots, or 4) have fibrous root systems. One experiment tests presence/absence of plant functional groups, grown in place twice in three years, on four farms. A field-scale design compares conventional fallow with CCM effects on soil water and nitrogen, and wheat yield on six cooperator’s farms. This research provides basic information on agro/economic impacts of CCMs.

Objectives/Performance Targets

  1. Position this project for maximal success by gaining familiarity with growth characteristics of targeted candidate species for CCM’s by growing crops locally in 2011 prior to potential award of this grant.

1a. We will produce seed of 8 – 12 crop species at Bozeman to gain greater familiarity with plant growth habit and obtain seed of known quality for research project.

1b. To ensure success of our field research, we will monitor nearby farm fields of CCM’s, as time and budget permits, to gain familiarity with sampling CCM’s and with practical field challenges.

  1. Quantify the effects of CCM’s (compared with fallow) on grain yield, quality, and economic return compared with fallow

2a. We will determine differences (with 90% confidence) in yield and quality of grain following each CCM compared to fallow for four plot studies and six field scale studies following the second year of the study.

2b. Based on grain yield, quality, seed costs, equipment costs, NRCS payments, etc. we will determine if the net economic return is different among the treatments. Our performance target is to identify soil-building CCM’s that produce similar or more profit in a CCM-wheat system than fallow-wheat, because otherwise adoption is relatively unlikely.

  1. Determine the effects of CCMs on soil quality using fallow as a control.

3a. Soil quality indicators that we will measure include biological (potentially mineralizable N (PMN), microbial biomass, enzyme activities, mycorrhizal colonization levels and infectivity potential, and earthworm density), physical (wet aggregate stability, temperature, compaction), and chemical (available nitrogen and phosphorus).

3b. Comparing CCMs with single functional groups to those with subsets or the entire set of functional groups, we will identify the functional group(s) that most contributed to any soil quality change detected.

3c. Indicators that are different between each CCM and fallow after the third year of the study will be identified. Our performance target is to identify which CCMs most improve different aspects of soil quality, allowing farmers to customize a CCM depending on their soil needs.

  1. Introduce growers and agricultural professionals (“audience”) to the potential sustainable aspects of CCMs.

4a. We will conduct one Field Day and two workshops during the first year of the project, focusing on general CC principles, and any regional research results (for example from ND). Our first performance target is to directly reach 200 people with these events, and indirectly reach another 800 by asking our audience to take handouts to neighbors, friends, and colleagues, and by producing a video of the Field Days that will be accessed online.

4b. Our second performance objective will be to increase the audience awareness and understanding of potential benefits of CCM’s. We will assess this with audience evaluations.

  1. Educate audience about effects of CCMs on subsequent crop and economics.

5a. In the winter after the wheat phase of this study, we will conduct three to four more workshops to share yield, quality, and economic results, have one radio interview with a PI, and produce a CCM webpage to share our findings. Our first performance target is to directly reach 300 people with these events and reach another 2000 indirectly.

5b. Our second performance target will be to increase our audience’s understanding of the agronomic and economic effects of CCMs in our region. This will be assessed with evaluations.

  1. Educate audience about the effects of CCMs on soil quality, including functional group benefits, based on our study.

6a. In the year of the second CCM crop, we will host another Field Day, conduct two to three more workshops to discuss our soil quality results, and prepare an Extension fact sheet on our findings. Our first performance target will be to directly reach 300 people with these events and 1,200 indirectly.

6b. Our second performance target will be to increase the understanding of plant functional groups, and to assess this with our educational evaluation plan.

  1. Enhance adoption, if study results warrant, of CCMs.


Field research in 2013 was conducted at plot-scale studies managed at four locations: near Amsterdam (45o 43’ 7.3” N, 111o 22’ 4.2” W), Conrad (48o 12’ 47.0” N, 111o 29’ 38.2” W), Dutton (47o 59’ 54.0” N, 111o 34’ 10.1” W), and Bozeman, MT (45o 40’ 12.0” N, 110o 58’ 39.9” W). Currently we are managing seven farm field studies, adjacent to the plot studies near Amsterdam and Conrad, with additional farm field sites near Conrad (48o 12’ 25.1” N, 111o 30’ 13.2” W), Dutton (47o 56’ 54.1” N, 111o 24’ 11.1” W and 47o 56’ 57.3” N, 111o 23’ 33.1”), Fort Benton (47o 56’ 3.7” N, 110o 51’ 3.5”) and Great Falls, MT (47o 31’ 7.4” N, 111o 8’ 27.1” W). We seeded plots in early May and terminated them in early July to provide better opportunity for pre-seed weed control, a more optimal growth window for cover crops, and to be consistent with current farmer practice. Cover crop growth was excellent in 2013. This year, four additional farmer-managed fields were sampled for biomass constituents and soil nitrate-N and water, while cereal grains were harvested from the three farmer-managed CCM fields from 2012 (total of seven farmer fields investigated 2012 – 2014). Data was still being processed at the time of this report, but it was notable that at the Conrad field site significant downy brome infestations remained on the chem fallow strip, while the CCM stubble had only a very low incidence.

Objective 1) Preliminary research was conducted in 2011 at the Bozeman experimental farm to examine growth of purported ‘root’ crops at different planting dates, with and without fertilizer N. Three commercially available lines of tillage radish grew similarly and produced large roots only at the mid-June seeding date. Beet did not grow well at the early planting date. Turnip was highly susceptible to flea beetles at all planting dates. Seed was harvested successfully at Bozeman for many, but not all, of the species used in this experiment. Radish is challenging to thresh to separate seeds from pods without damaging the seed. Two grower fields were sampled to measure CCM biomass proportions, soil water and N, and subsequent wheat yield. CCM biomass was found to be strongly biased in favor of N-fixing pea in both fields, which may be expected in typically N-limited cereal stubble. This raises a key question of whether some amount of starter N is required to obtain balanced CCM biomass proportions, and we are fertilizing at experimental sites to ensure available N is not severely limiting. In one case were it was measured, wheat yield did not differ statistically (P=0.14) between CCM (53.6 bu/ac) and chem fallow (60.4 bu/ac), although grain protein was greater (P=0.02) for fallow (12.6%) than CCM (11.4%).

Objective 2) Spring wheat was hailed out >95% in a devastating hail storm August 1, 2013, that wreaked havoc over much of the Gallatin Valley. Residual grain yields were harvested, but this data is not likely to be of value. Spring wheat yield was harvested at the Conrad site, and data has not yet been fully summarized. Although overall yields were excellent due to timely and ample rainfall, it is apparent that wheat yield was lower on many of the cover crop treatments compared with chem fallow under all three fertilizer N regimes. This was especially true for the ‘pea’ control and the ‘nitrogen fixers’ only treatments, which were not effectively killed by high rates (32 oz/ac) of glyphosate in 2012 and so continued soil water use.

Objective 3) Several biological, chemical and physical soil parameters were measured preliminarily for the ‘Full Mix’, ‘Pea only’, and chem fallow treatments. This data is still being summarized but early indications were that one appearance of cover crops had no measurable effect on most soil parameters, including biological indicators related to enzymes, microbial biomass and mychorrizae fungi. However, potentially mineralizable N was greater than chem fallow for both the pea and full mix treatments at two locations, and daily maximum soil temperatures at a two-inch depth were cooler by as much as 16oF under most cover crop treatments, compared with chem fallow. This cooling effect persisted for about a month before the cover crops were terminated until about a month after chemical termination. We hope to explore the potential value of this cooler soil surface microclimate in additional studies. Because most soil parameters are slow to change, we are making the majority of soil quality measurements after the CCM treatments have been grown for the second time in all plot studies. This is a targeted strategy to fast-forward the soil change response.

Objective 4) We are making strong efforts to raise awareness of cover crops appropriately in various venues. We conducted a Field Day on June 14, 2012, at the Amsterdam site where we had about 50 attendees and will host another July 8, 2014 at Conrad, MT. Dr. Miller discussed cover crops at a major field day (200 attendees) near Havre MT, June 26, 2013. Drs. Jones and Miller have also given several cover crop presentations to various grower audiences (totaling several hundred attendees) since this project commenced (NRCS Conservation Districts Winter Trend Series – Shelby, MT, 12/6/2011; Northern Pulse Growers Association Pulse Days – Billings, MT, 12/13/2012; Montana Farmers Union Annual Winter Conference – Great Falls, MT, 10/12/2013; Montana Grain Growers Assoc. Annual Conference, Great Falls, MT, 12/3/2013; Montana Seed Trade Assoc. Annual Meeting, Helena, MT, 12/10/2013). Dr. Miller was invited to present a seminar at the American Society of Agronomy meeting in Tampa, FL, 11/6/2013, on the topic of cover crop use in the semiarid Great Plains []. Project PIs have participated in live video-link research updates designed to inform engaged MSU colleagues and the NRCS State Agronomist of the most current research findings about cover crop use in Montana (March 2013 and January 2014). We have hired a videographer, who has interviewed five growers to date and taken both aerial and ground shots of one of our sites to be used in the video. This video can be viewed on Dr. Jones’ soil fertility website []

Objective 5) Economics of cover crops cannot be addressed until conclusion of the project but already it has become evident that seed cost will be a key factor. It appears that some farmers are willing to ‘invest’ in soil quality if they believe there will be a long-term return as Dr. Miller has shown from related research in a long-term study at Bozeman.

Objectives 6 and 7 must wait until the final year of the study.

Impacts and Contributions/Outcomes

It is premature to comment on regional impacts from this research. However, we have already learned useful information about the most sensible growth period to use cover crops, and it appears that RMA is revisiting summer fallow insurance restrictions based on research from us and others. Another contribution may relate to using balanced seeding rates of different crops if the desire is to create balanced cover crop biomass. Using seeding rates for optimal grain production may bear little relation to cover crop goals and should be reconsidered. The northern Great Plains is known for relatively low input agriculture, and it is likely that cover crops will follow this dictum and provide the lowest cost seed sources that still accomplish targeted soil management goals. Since this is the first replicated research on CCMs in Montana, negative or positive results can be expected to yield economic value. Negative results may save farmers from losses over a larger scale by avoiding the use of CCMs in inappropriate contexts, while positive results may help direct desired change in soil parameters, with farm-specific benefits anticipated.


Herb Oehlke
22 miles east of Conrad
Conrad, MT 59425
Office Phone: 4066272184
Chad Doheny
2490 22nd Lane NE
Dutton, MT 59733
Office Phone: 4067884122
Carl Vandermolen

56 Park Plaza Road
Bozeman, MT 59715
Office Phone: 4065871288
Will Roehm
east of Great Falls, next to Maelstrom Air Force base
Great Falls, MT 59405
Office Phone: 4067883199
Jane Holzer
Montana Salinity Control Association
PO Box 909
Conrad, MT 59425
Office Phone: 4062783071
Jim Bjelland
21 miles east of Conrad
Conrad, MT 59425
Office Phone: 4067883666
Susan Tallman
M.Sc. Student
Montana State University
334 Leon Johnson Hall
Bozeman, MT 59717-3120
Office Phone: 4065873977
Clain Jones
Assistant Professor
Montana State University
334 Leon Johnson Hall
Bozeman, MT 59717-3120
Office Phone: 4069946076
Dr. Cathy Zabinski
Associate Professor
Montana State University
334 Leon Johnson Hall
Bozeman, MT 59717-3120
Office Phone: 4069944227
Roger Benjamin

10 miles NW of Fort Benton
Fort Benton, MT 59442
Office Phone: 4067885142