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

2014 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 tested effects of cover crop mixtures (CCMs) grown during the summerfallow period on soil biological, chemical, physical, and water 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 seven collaborating farm fields. This research provides information on agronomic impacts of CCMs.

Objectives/Performance Targets

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

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

Obj. 2 – Quantify the effects of CCMs (compared with fallow) on grain yield, quality, and economic return compared with fallow.

a. 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.
b. 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 CCMs that produce similar or more profit in a CCM-wheat system than fallow-wheat, because otherwise adoption is relatively unlikely.

Obj. 3 – Determine the effects of CCMs on soil quality using fallow as a control.

a. 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).
b. 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.
c. 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.

Obj. 4 – Introduce growers and agricultural professionals (“audience”) to the potential sustainable aspects of CCMs.

a. 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.

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

Obj. 5 – Educate audience about effects of CCMs on subsequent crop and economics.

a. 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.
b. 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.

Obj. 6 – Educate audience about the effects of CCMs on soil quality, including functional group benefits, based on our study.

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

Obj. 7 – Enhance adoption, if study results warrant, of CCMs.


Field research in 2014 was continued in four plot-scale studies (Amsterdam, Bozeman, Conrad, Dutton, MT). We completed monitoring of seven (eight) farm fields (Table 1) where wheat test yield and quality data is pending (Februay 2014) for three sites. We have one growing season remaining on the plot-scale studies, and the farm-scale study is pending analysis of wheat yield and quality at one remaining site that should be completed by February 2015.

Objective 1) This was reported in previous reports.

Objective 2) Agronomic assessment was conducted at both field (farmer-operated, nearly complete) and plot scales (MSU in-depth research, ongoing). Unless cereal crop yield (or protein for wheat) is improved by cover crops, economic comparison is obviously negative due to added costs for managing a cover crop (disregarding temporary USDA incentive payments). Agronomic comparison of cover crops and chem fallow, at both field and plot scale, is reported below.

2a. Field scale.

Field operations for this cover crop studies were conducted by the participating farmers, as advised by personnel outside of MSU (i.e. USDA-NRCS; Montana Salinity Control Association advised farmers on seed mixtures and planting/ termination dates). Our role was to objectively document soil water and nitrate-N and subsequent crop yield and protein following cover crops, compared to an adjacent chem fallow control (Table 1). We collected geo-referenced crop and soil samples systematically along the length of the cover crop – fallow interface (usually every 80 – 100 feet) and at randomly assigned distances from the interface (from 50 to 250 feet), avoiding potential machinery overlap areas near field edges. This usually resulted in 12 samples from both the cover crop and fallow field area. We committed to monitoring six total farm field sites in our proposal, but ultimately seven were attempted (two were completely hailed out during the test crop phase). In this report we also include one farm field site that provided preliminary data to support this proposal, for a total of eight.

At all farm sites, cover crop biomass was unevenly distributed among species and typically dominated by pea, turnip, and/or oat (Figs. 1-8). Biomass totaled from 900 to 2600 lb/ac (oven dry weight) among fields and years (Table 2). Note that weeds contributed trivially to biomass at most sites. Compared with a chem fallow control, cover crop mixtures depleted soil water to a depth of 3 feet by an average of 2.9 inches (range = 0.7 to 5.9) and soil nitrate-N by an average of 54 lb/ac (range = 22 to 86) (Table 2). Except for one site (Great Falls), subsequent cereal crop yield and/or protein was depressed significantly following cover crops, consistent with soil water and nitrogen measurements.  

2a. Plot scale. Field research in 2014 was continued in plot-scale studies at four locations: near Amsterdam (45.72oN, 111.37oW), Conrad (48.22oN, 111.48oW), Dutton (48.00oN, 111.57oW), and Bozeman, MT (45.67oN, 110.98oW). For consistency with grower practice, we seed cover crop treatments in early May. Timely growing season rainfall resulted in relatively high biomass production, averaging 2500 and 2100 lb/ac at Amsterdam (weed biomass was almost entirely volunteer wheat) and Conrad, respectively. We manage our cover crops by aiming for equal plant density for all species components within a mixture and for a constant 11 plants per square foot among treatments. Plant emergence targets were generally achieved and little practical difference existed in total biomass amongst treatments (Fig. 10). Differences among subsequent wheat yield and quality will become most interesting in 2015 and 2016 after the second iteration of cover crop treatments at each site which was not budgeted as part of this project (we are seeking other funds to enable completion of the year 4 test crop phase). At two locations in 2014 it was evident that the type of cover crop biomass was important, with the best wheat yield and protein occurring after the nitrogen-fixing treatments (Pea and NF). At Dutton, note that Pea and NF were the only two treatments that did not differ from summerfallow for either yield or protein (Fig. 11). A likely reason for this difference in subsequent crop effects, compared with the field scale study, is that termination is managed at a two-three week younger plant stage in the plot-scale research which limits soil water use compared with the farm field study, and legume species contribute to soil nitrogen. Economic assessment of cover crops is premature prior to two conditions being met. First, it is crucial that cover crop management is understood sufficiently well that it might be managed optimally relative to costs and returns. Second, it is apparent that soil quality changes slowly and so any economic assessment is best made over a suitably long time frame. Based on our results to date, it is very evident that incentive payments from USDA are crucial to developing this practice to be economically optimal on farms in Montana. Early indications from this research show that legumes, compared with non-legumes, are crucial to managing soil nitrogen that might benefit subsequent crop yield and protein. Given that legume seeds are typically the most expensive portion of a seed mix, due to larger seed size, this may present an additional challenge for understanding economically optimal seeding rates for legume cover crops.

Objective 3) Biological, chemical, and physical soil parameters were measured preliminarily for the ‘Full Mix’, ‘Pea only’, and chem fallow treatments after one year of cover crop growth. This data has been summarized as part of a M.Sc. thesis (COVER CROP MIXTURES AS PARTIAL SUMMERFALLOW REPLACEMENT IN THE SEMI-ARID NORTHERN GREAT PLAINS – Susan Tallman, April, 2014 – Montana State University – Bozeman) and shared appropriately with various farmer and advisor audiences. 

3a. Soil quality indicators have been assessed just prior to wheat seeding for all four sites after a single year of cover crops and very few differences were found, as was expected at this early juncture. Potentially mineralizable N (measure of soil organic nitrogen) was greater for either Pea or the ‘Full’ cover crop treatment at three of four sites demonstrating the potential of cover crops to change soil even under these dry climatic conditions. Microbial biomass was significantly greater for either the pea or ‘full’ biomass treatments, compared with summer fallow, at the two more recent sites where cover crop management coincided with more favorable weather and refined research techniques. We noted soil cooling at a 2-inch depth from cover crops (as much as 20oF cooler than summerfallow) persists up to a month after termination. Soil nitrate (but not phosphorus) was depleted by cover crops compared with summerfallow, although less so for legume-only cover crop treatments. Soil compaction and wet aggregate stability have not differed between cover crop treatments and summerfallow to this point.

3b. More refined comparisons among all CCM treatments will begin in 2015 after the second iteration of cover crops prior to spring wheat seeding.

3c. More refined assessment of soil quality changes awaits soil measurement after the second iteration of cover crops at all sites. This information is intended to guide Montana farmers in customizing cover crop practices for their farm.

Objective 4a and 4b.  We met these goals in the first two years of the study as described in past two annual reports.

Objective 5a and 5b.   How we met these goals were described in last year’s annual report. We continue to maintain the CCM webpage and Clain Jones was interviewed on the Northern Ag Network in June 2014 about this study and about our field day (described below).

Objective 6a. May 22, 2014, Perry Miller was invited to a policy summit in Kansas City, MO, to present cover crop research findings to various USDA agencies (NRCS, RMA, Wildlife) and the National Crop Insurance Council. We held a Field Day in 2014 on July 8 at our Conrad study site to present the benefits and challenges of cover crops and describe what we have learned from the study so far. The farm tours were advertised by a MSU press release, press releases targeted to the regional newspapers, and public service announcements on regional radio stations. In addition to our advertising and organizing, we received support from the National Center for Appropriate Technology, the NRCS, and local Conservation District. Of the 60 attendees, 13 filled out the audience evaluation. Those who filled out a field day evaluation said that their awareness and understanding was improved, and that they would share with others. Dr. Miller’s and Dr. Jones’s presentations at this Field Day were recorded and posted to youtube this Fall (links below) and have received over 250 views.

The project team also presented results from this study at four workshops and one national webinar (see Table below), reaching a total of 435 people which surpasses our goal of 300 direct contacts. We also wrote a press release on mixed cover crops as part of our advertising for the field day. Although indirect contacts are unknown for our press release and radio interview, our youtube videos have received over 2,500 views, exceeding our indirect contact goal. 

Objective 6b.  We will write an Extension fact sheet on our study results later in 2015 when we have a more complete data set. We will soon send out a survey to approximately 400 Montana producers, asking about their perceptions and experiences with cover crops, what they have learned from our research to date, and the type of research they would find useful in the future.

The following 5 videos are posted on YouTube:

  1. Cover Crop Research by MSU: Part 1 – Perry Miller highlighting cover crop management. Posted September 2014, 146 views by end of 2014.
  2. Cover Crop Research by MSU: Part 2 – Clain Jones presenting the chemical and physical impacts of cover crops on soils. Posted September 2014, 122 views by end of 2014.
  3. Mixed Cover Crops: An introduction. Effects of cover crops on soil quality in semi-arid regions. Posted December 2013, 2186 views by end of 2014.
  4. Susan Tallman’s thesis defense on the effect of different cover crop mixtures on subsequent yield and soil quality. Posted May 2014, 84 views by end of year 2014.
  5. Mixed Cover Crops – Clain Jones discusses past and ongoing research projects in the state on the effectiveness of cover crops at the October 2013 Montana Farmers Union state meeting. 805 views by end of 2014.

Extension presentations on cover crops are listed in Table 1. Links to the presentations and videos are posted on the cover crop webpage (

Impacts and Contributions/Outcomes

This research project is likely to impact strongly USDA-NRCS policy for cover crop adoption in semi-arid Montana and similar regions. Given that cover crops are being promoted aggressively for soil improvement by USDA, it is crucial to understand the interaction of cover crop management and soil-climatic context. This research is targeted at greening summerfallow and has best applicability in regions that retain a high proportion of summerfallow within crop rotations and in a similar soil-climatic context. Soil change occurs slowly, and it is important to match grower expectations accordingly. With our monitoring of farmer-conducted, USDA-NRCS-advised on-farm trials we provide objective data that demonstrates the real challenge of managing soil water and nitrogen in the immediate term. With our plot scale studies, where we grow cover crops twice in three years to accelerate soil change, new information will be provided for how plant functional groups differ in their impacts on soil and subsequent crops. It is possible that an even longer term for observation would be needed to document the full potential value of cover crops for changing soil. Perry Miller was invited to summarize his cover crop research findings (including this current study) at a USDA policy summit in Kansas City in May 2014. While there it became evident how rare long term research on cover crops is, and how precariously national policy must be set in the absence of robust regional research. It is premature to comment in more detail on regional impacts from this research. However, we have already learned useful information (presented above) about the most sensible growth period to use cover crops, and it appears that the special role of legumes is being illuminated. The northern Great Plains is known for 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. It is important to note that we have focused on an agricultural region that contains relatively few livestock, and therefore have not integrated livestock grazing in this study, which may be an important part of the puzzle for making economic sense of annual cover crop mixtures.


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