Cover Crop Grazing: Optimal Seasonality for Soil and Livestock Benefit

Cover Crop Grazing: Optimal Seasonality for Soil and Livestock Benefit

Summary

We explored the effects of cool- and warm-season cover crop mixtures, with and without grazing, on soil properties and spring wheat yield in two plot-scale studies in southwestern Montana. Cover crop mixtures terminated with herbicide (‘brown manures’), grazing, or haying, and compared with chem-fallow. Based on equal growing degree days, cool-season biomass production (4.5 Mg ha^-1) was <10% greater (p = 0.03) than warm-season biomass at Fort Ellis (2015), but at the north Gallatin Valley (NGV) location, cool-season biomass (2.4 Mg ha^-1) was more than double (p <0.01) the warm-season biomass. Thus, warm-season cover crops may need to be sown earlier in the growing season (mid-May) in order to optimize growing season rainfall and achieve adequate biomass for grazing. Forage quality of the warm-season mixes were generally superior to cool-season cover crop mixes.

When measured after termination at both sites, soil under cover crops contained 5-8 mm (0.2-0.3 in) less soil water and 21-27 kg ha^-1 (18-24 lb ac^-1) less Nitrate-N than chem-fallow (P<0.01). When Fort Ellis was resampled Apr 13, 2016, prior to spring wheat seeding, soil water did not differ importantly among any treatments, but soil Nitrate-N was 41 kg ha^-1 (37 lb ac^-1) less under cover crops treatments than chem-fallow, while soil phosphate was 16 kg ha^-1 (14 lb ac^-1) greater (p = 0.03). We did not fertilize the cover crops so the general phosphate increase was surprising. Warm-season cover crop mixes used less soil water than the cool-season mix at Fort Ellis (0.2 in; p <0.01) but did not differ at the NGV site, despite much lower biomass for the warm season mix there. At both sites, the warm-season mix used 5–6 kg ha^-1 (4-5 lb ac^-1) less soil Nitrate-N than the cool-season mix. When re-measured at Fort Ellis Spring 2016, this difference increased to 17 kg ha^-1 (15 lb ac^-1). Cover crop treatments had 31% greater acid (p <0.01) and 19% greater alkaline phosphatase activity (p = 0.04), as well as 26% greater β-glucosidase enzyme activity (p = 0.05), than chem-fallow. Note that enzyme activity was measured 9-10 mo following a brief period of mob grazing (~24 hr). Potentially mineralizable N and microbial biomass measurements generally did not differ among cover crop treatments and chem-fallow.

Wheat grain protein was 3 g kg^-1 (0.3%-units) lower (p <0.01) in cover crop treatments, and 0.22 Mg ha^-1 (3.7 bu ac^-1) less yield (p = 0.06), compared with chem-fallow. There were no differences in wheat yield or quality amongst cover crop treatments.

Objectives/Performance Targets

The purpose of this research was to investigate the effects of integrating livestock grazing in dryland wheat-cover crop systems. The study objectives were:

Livestock Grazing Objective

1. To evaluate both cool- and warm-season annual cover crop mixtures for potential forage in dryland wheat-cover crop systems

 Soil and Objective

2. To investigate how grazing cover crop mixtures as a termination method affects soil biochemical properties in comparison to using herbicide for crop termination.

Agronomic Objective

3. To assess how changes in soil properties, catalyzed by grazing, affect subsequent wheat yields.

Educational Objectives

4. To increase local producer knowledge of cover crop mixtures performance as forages/graze and termination methods and potential benefits for soil quality.
5. To provide local producers with information regarding the potential benefits of ICLS and methods of ICLS adoption in Montana through scientific and extension publications.

Materials and Methods

Site Characterization

The first study site was the Montana State University – Fort Ellis Research Farm (N 45.667°, W 110.978°) located near Bozeman, MT. The site was planted in barley during the 2014 growing season and has been under no-till management since 2012. The predominant soil type at the Fort Ellis Research Farm is Blackmore silt loam and the mean annual rainfall is approximately 500 mm. Fort Ellis was planted in cover crops in 2015, followed by spring wheat in in 2016 (cv. Duclair). Also in 2016, a second site in northern Gallatin valley, MT (NGV) was established in partnership with local producer, Jason Camp. The site was sown to winter wheat during the 2015 season and alfalfa before that. This field site experiences less annual rainfall (~360 mm) with a predominant soil type of Amsterdam silt loam and is representative of large portions of southwestern Montana (Tables 1 and 2).

Study Design

The study was a randomized complete block design consisting of six cover crop/termination treatments (mainplot: 15.2 m x 7.6 m) with a split plot arrangement and four replications. Each cover crop mixture consisted of cereal, legume, and brassica crops. Cereal species were oat (Avena sativa L. cv. Oatana) in the cool-season mixture and sorghum (Sorghum bicolor L. sp.- 2015) and millet (Panicum lilacceum L. sp.- 2016) in the warm-season mixture. Legume species used included forage pea (Pisum sativum L. cv. Arvika) in the cool-season mixture and soybean (Glycine max L. sp.) in the warm-season mixture. Radish (Raphus stivus L. sp.) was the brassica used in both the cool-season and warm-season mixes as its growth pattern is daylength-sensitive (radish bolts if planted prior to mid-June, otherwise remains vegetative and forms large root). Cover crops species were seeded in the same row (spacing: 30 cm) to a depth of 2.5 cm with a low-disturbance disk seeder. Seedling rates were calculated by dividing a recommended monoculture rate proportionally by the number of species in the mixture. Each mixture was seeded at a target rate of 120 m² with individual cover crop species added to a mixture at a target seed rate of 40 m². Termination of cover crop coincided with first-bloom of pea in the cool-season mixtures (McCauley et al. 2012; Table 3). Termination of warm-season cover crop mixtures was determined by the accumulation of growing degree days (GDD; T_base = 0°C) of the cool-season mixture. Warm-season cover crop growth in GDD was matched as closely as possible to the cool-season cover crop growth in GDD.

Treatments and cover crop mixes for year-1 (Fort Ellis) and year-2 (NGV) are listed in Table 4. The chemical-fallow (fallow), served as a control treatment. In cool-season grazing (cool graze) and warm-season grazing (warm graze), lambs were used to ‘graze-out’ cover crops. However, after grazing, the cool graze treatment was sprayed within a month of grazing to ensure complete termination of cover crops and therefore preserve soil moisture and in consideration that re-growth is likely insufficient to economically warrant repeated grazing. The warm graze and warm-season haying (warm hay) were not sprayed after grazing/swathing as the first frost in the Bozeman area typically occurs mid-September and terminates re-growth of warm-season cover crop foliage. The last two years have incurred an exceptionally late first fall frost (Table 3). Radish is frost tolerant and can withstand temperatures as low as -4 °C (NRCS, 2009). Cool-season spraying (cool spray) and warm-season spraying (warm spray) were terminated with glyphosate and left as a ‘brown manure’ (Table 3). The cool spray and warm spray provide a comparison in termination method to the cool graze and warm graze, respectively. In the warm hay, cover crops were swathed and then killed by frost in order to isolate the effect of cover crop biomass removal on edaphic and agronomic parameters. However, in year-2, due to low biomass growth, warm hay was swathed and the biomass was left on the plots to simulate mowing. 

In year-2, all main plots at Fort Ellis were seeded in spring wheat (cv. Duclair) with a low-disturbance drill to a depth of 2.5 cm, perpendicular to year-1 cover crop seeding. Nitrogen fertilizer treatments subplots were banded at >5 cm below and to the side of the seed at three rates: 0, 67.5, and 135 kg N ha^-1.

Cover Crop Sampling

Cover crop population stand counts were conducted 4 wk after planting in four 1 m strips per plot totaling ~1 m² area. Cover crop count plots were at least 0.5 m from any treatment plot edge in order to avoid edge effects.

Glyphosate herbicide application, sheep grazing, and swathing were used in cover crop termination. Cover crop mixtures in the grazing treatments were sprayed with glyphosate approximately two weeks after the cessation of grazing to ensure full termination. The cover crop mixtures in the warm-season swath treatment were swathed on the same day in which the other two warm-season treatments were grazed and sprayed, respectively.

Above-ground cover crop biomass for all plots was sampled in the same areas used for seedling counts by cutting to the soil surface within 24 hr of termination. Grazed and swathed plots, were resampled similarly within 48 hr after termination to measure residual biomass. All samples were dried at 50°C prior to weighing. For warm-season cover crop treatments, enlarged radish roots below soil surface were dug and measured as biomass. After drying, cover crop samples were ground and analyzed for C and N using a LECO combustion analyzer (LECO Corp., St. Joseph, Michigan).

Cover crop forage quality samples were taken from all grazed and swathed treatments pre- and post-termination (including cool-season re-growth prior to glyphosate application). All samples were sent to Midwest Laboratories (Omaha, NE) and analyzed for fiber, protein, nutrient and mineral content with NIR spectroscopy.

Soil Sampling and Laboratory Procedures

Soil compaction was measured in 2015 and 2016 with a hand-held static cone penetrometer (Durham Geo-Enterprises Inc.- Nova Metrix, Wakefield, MA). Six measurements were taken from each treatment within a week seeding at relatively uniform soil moisture content (required for accurate comparison). Additionally, soil bulk density was measured prior to seeding in both years, which may be a more reliable measure of soil compaction as it is not so sensitive to soil water content. Site bulk densities, by depth, were determined by averaging all values for each block and used to calculate Equivalent Depth (mm) of soil water to a depth of 0.91 m (Or and Wraith 1999). Soil water was measured prior planting cover crops or wheat. In cover crop years, soil water was additionally measured after cool- and warm-season cover crop termination, respectively. The gravimetric weight loss method was used to calculate soil water content.

Soil nitrate was measured using the same cores as soil water (depth of 0.91). Samples were oven dried at 50°C and sieved through a 5 mm sieve. After sieving, 5 g of soil was added to 25 mL of 1 M KCL, shaken for 30 min, filtered through a Whatman 5 filter, and then analyzed on a Lachat flow injection analyzer (Lachat Instr., Loveland, Colorado).

Soil P was measured by collecting six soil cores to a depth of 15 cm in each plot and processing samples by adapting methods from Olsen and Sommers (1982). Samples were oven dried (50°C) and sieved (2-mm). After sieving, 1.25 g of soil was added to 25 mL of 0.5 M NaHCO₃ (pH 8.5), shaken for 30 min, and then filtered through a Whatman 5 glass fiber filter. Then, 5 mL of soil solution was combined with H₂SO₄ acid as described in Kuo (1996) and analyzed by spectroscopy at 880 nm.

Potentially mineralizable nitrogen (PMN) was measured by collecting six 15 cm soil cores from each plot. The soil probe was sterilized with isopropyl alcohol between plots to prevent sample contamination. PMN is calculated as the difference in plant available N at time zero and after incubation for 14 d at 30 ^oC (Keeney 1982). Time zero plant available was measured using 5 g oven-dried equivalent soil and the same method noted previously for soil nitrate extraction. To calculate plant available N after incubation, three 5 g oven-dried equivalent, field moist soils samples from each plot were added to 12.5 mL of double-deionized water and held under a flow of N₂ gas for five seconds in order to create a nitrogen atmosphere. Next, 12.5 mL of 2 M KCl was added to each sample and incubated in a hot water bath at 30°C for 14 days. After incubation, samples were filtered through a Whatman 5 filter and analyzed on a Lachat flow injection analyzer. The three incubated samples from each plot were averaged prior to statistical analysis. PMN was reported as the amount of NH₄ after incubation minus the amount measured prior to incubation.

Microbial biomass was calculated from the same soil cores collected for PMN and using Soil Induced Respiration method modified from West and Sparling (1986). A 5-g field-moist soil sample was added to 10 mL of yeast solution and shaken horizontally at 20°C for 4 hr. Headspace CO₂ concentrations, caused by microbial respiration, were measured after 10 min of shaking (Time 0), after 2 hr of shaking (Time 2), and after 4 hr of shaking (Time 4). Headspace CO₂ concentrations were measured using gas chromatography (Varian Inc., Palo Alto, CA).

Soil enzyme activity was measured from the same soil cores as PMN and microbial biomass and analyzing samples using methods adapted from Parham and Deng (2000) and Dick (2011). Specific enzymes targeted were: β-glucosidase (EC 3.2.1.21; cleaves celloboise from cellulose), β-Glucosaminidase (EC 3.1.2.52; cleaves N-acetyl glucosamine from chitin), and acid and alkaline phosphatase (EC 3.1.3.1, EC 3.1.3.2; cleaves phosphates from organic phosphorus compounds). One-g field-moist soil was inoculated in duplicate with a p-nitrophenol (pNP)-labelled substrate for each enzyme substrates, incubated for 1 hr at 37°C, and then analyzed for pNP using a spectrophotometer (Parham and Deng, 2000).

Wheat Sampling

Spring wheat biomass samples were taken in two 1-m strips from each fertilization subplot at anthesis. Plants were cut at the soil surface, dried at 50°C, and weighed after drying. A plot combine (Wintersteiger, Salt Lake City, UT) was used to harvest wheat from each treatment plot and N fertilization subplot. Yield was determined by grain weight per harvested area. A NIR transmittance machine (Infratec GmbH, Dresden, Germany) was used to analyze wheat for protein and moisture content.

Statistical Analyses

All statistical analyses were performed with R statistical software (The R Foundation for Statistical Computing, Vienna, Austria; version 3.2.5). Data were examined for normality and homogeneity of variance using residual and Q-Q plots. Linear models built with treatment and block (rep) as independent variables and analyzed with ANOVA were used in all parameter analyses except for wheat parameters. For wheat parameters, a linear model was built with cover crop treatment (previous year), block, and fertility subplot as independent variables and analyzed with ANOVA. Statistical differences were determined using Fisher’s Protected Least Significant Difference (LSD) Test with no p-adjustment and α = 0.05 (package: agricolea). Pre-planned orthogonal contrasts were used to compare combinations of cover crop and fallow treatments. Tables 1-4

Accomplishments/Milestones

Objective 1

The first objective of this study was to evaluate both cool- and warm-season annual cover crop mixtures for potential forage in dryland wheat-cover crop systems. In the NGP, both forage quality and quantity affect the monetary value of hay and pasture. In terms of cover crop quantity, pre-termination biomass ranged from 4.0 Mg/ha (warm graze) to 4.65 Mg/ha (cool graze). Taking into account that the average field in Montana yielded 4.6 Mg/ha of hay for all hay types and 3.6 Mg/ha for non-alfalfa hay (MDOC, 2017), the range of biomass production across all treatments at Fort Ellis in 2015 shows comparable cover crop biomass production to other hay fields in Montana (Table 5). Cool-season biomass was <10% greater than warm-season biomass (p = 0.03) in 2015. This is likely due to the fact that the cool-season treatments received 95 mm of precipitation between seeding and termination while the warm season treatments received 21 mm of precipitation between seeding and termination and only 4.3 mm precipitation during the last 13 d of growth. Cool-season biomass was ~170% greater than warm-season biomass (p <0.01) in 2016. While the cool-season treatments received 96 mm of precipitation between seeding and termination, the warm-season treatments received only 6.1 mm between seeding and termination. June of 2015 and June 2016 were the driest Junes on record since 2003 at the NGV and since 1985 at Fort Ellis, respectively. These irregularly dry Junes and their effect on cover crop biomass production do not accurately reflect biomass production potential in years which receive growing season precipitation closer to the LTA.

These data imply that cover crops mixtures, especially spring-sown mixtures, in areas of the NGP with higher annual rainfall (>350 mm), may produce adequate biomass (i.e. forage) for grazing. However, in drier areas of the NGP (< 350 mm annual precipitation), cover crops may not produce comparable amounts of forage compared to other hay production lands. Furthermore, the spring-centric precipitation patterns of the NGP may not be conducive to high levels of warm-season cover crop biomass production. While utilizing cover crops as a tool for encouraging agroecological diversity on the landscape scale by engaging the warm-season plant growth period, warm-season mixtures may not produce adequate forage quantity for grazing in drier areas or in years of drought. One solution to this issue may be to plant warm-season cover crop mixtures earlier in the year (mid-to-late May) in order to ensure sufficient precipitation for biomass optimization.

In terms of cover crop quality, cover crop treatments differed with regard to crude protein (CP; p = 0.02), acid detergent fiber (ADF; p = 0.02), neutral detergent fiber (NDF; p = 0.01), and total digestible nutrients (TDN; p = 0.02) in 2015 at Fort Ellis (Table 6). At the NGV in 2016, treatments differed with regard to CP (p < 0.01), ADF (p = 0.02), and TDN (p = 0.02).

Values for CP and TDN were higher in the warm-season mixtures than in the cool graze treatment at in both 2015 (p <0.01, <0.01) and 2016 (p <0.01, 0.01). The same contrast, cool v. warm, also showed strong evidence that ADF was lower across warm-season treatments than in the cool graze treatment in both 2015 (p <0.01) and 2016 (p = 0.01). The warm graze mixture had the highest numerical relative feed value (RFV) in both years, differing from other treatments in 2015 (p = 0.02), but not in 2016 (p = 0.20).

Objective 2

The second objective of this study was to investigate how grazing cover crop mixtures as a termination method affects soil biochemical properties in comparison to using herbicide for crop termination. A major point of concern when grazing cropland is the potential for soil compaction to occur (Hamza and Anderson, 2005; Bardgett and Wardle, 2010). Table 7 summarized soil penetration resistance among all plots prior to spring wheat seeding and following cover crop mixtures in 2015. The omnibus ANOVA shows differences for compaction due to proceeding cover crop treatments at the 7.5-15 cm depth (p <0.01) and 15-22.5 cm depth (p <0.01), but no differences at other depths. There was a trend across all depths where cool-season plots had higher mean compaction values than warm season plots and fallow plots. In exploring this trend further, it is useful to examine the contrast p-values which show differences between warm- and cool-season cover crop treatments, as well as differences between the fallow and all cover crop treatments at the two middle depths. Analysis of soil bulk density data prior to seeding spring wheat at Fort Ellis in 2016 (Table 8) also showed no sign of compaction at any depth, furthering the conclusion that grazing did not compact soil. While the cause of the trend noted in soil penetrometer data (Table 7) is difficult to pinpoint, the major take away from these data is that livestock grazing did not significantly impact soil compaction at the Fort Ellis study site. However, sheep only grazed plots for ~24 hr in low densities (6 lambs/plot) and that may not be reflective field- and herd-scale cover crop grazing.

Table 9 shows soil water following cover crop termination differed among treatments across all depths at both Fort Ellis (2015; p < 0.01) and NGV (2016; p <0.01). The fallow versus all other treatments and cool- versus warm-season treatments contrasts also showed strong evidence of a difference across all depths at both Fort Ellis (2015; p < 0.01) and NGV (2016; p <0.01). In 2015, at Fort Ellis, fallow treatments post-warm-season cover crop termination had an average of 40% more soil water than all other treatments. In the same comparison in 2016, at NGV, fallow treatments post-warm-season cover crop termination had an average of 26% more soil water than all other treatments. In 2015, (Fort Ellis) warm-season treatments had an average of 25% more soil water than cool-season treatments after termination; while, in 2016 (NGV), warm-season treatments had an average of 3% more soil water than cool-season treatments after termination.

Soil NO₃-N levels following cover crop termination at Fort Ellis (2015) were different among treatments at the 0-0.3 m (p <0.01) and 0.31-0.6 m depths (p <0.01; Table 10). Post-cover crop termination soil NO₃-N levels at the NGV (2016) differed among treatments at all three depths (p <0.01). The general pattern of NO₃-N levels immediately following cover crop termination at both site-years was fallow > warm-season > cool-season. Prior to spring wheat seeding at Fort Ellis in 2016 (Table 11), the order after cover crop termination in 2015 was augmented so that fallow > cool-season > warm-season, which may signify more cover crop litter breakdown in cool-season treatments. These patterns are likely the result of NO₃-N use by cover crops. Other studies (Biederbeck et al., 1996; Miller et al., 2006; van Kessel and Hartney, 2000) have noted similar short-term losses of soil NO₃-N following cover cropping. This is likely the result of N immobilization plant residues. The long-term effects of cover cropping on soil NO₃-N show a net increase in some instances (Sainju et al., 2002; Jones et al., 2015b), but require further study in order to understand how the long-term break-down of cover crop litter affects soil NO₃-N.

Potentially mineralizable nitrogen (PMN) did not differ (p = 0.07) among treatments prior to spring wheat seeding at Fort Ellis in 2016 (Table 12). However, the contrast between spray- and graze-terminated treatments favored spray-terminated treatments (p = 0.01) with 63% greater PMN than graze treatments. This is likely due to the effect of grazing on plant litter breakdown. Livestock intestinal tracts and rumens enhance the rate of plant material decomposition so that animal waste is already at an advanced state of decomposition relative to other litter of the same age (Wardle and Bardgett, 2004). This enhanced litter (animal waste) is highly labile and easily assimilated into the below-ground food web (Wardle et al. 2002, Ruess and Ferris 2004). Therefore, it is possible that the differences between spray and graze treatments are related to microbial uptake of soil N with higher rates of soil microbial N uptake occurring in the graze treatments. More long-term study of PMN dynamics in grazed cover cropping systems may shed more light on the effects of grazing on PMN.

Table 11 shows soil water and soil NO₃-N prior to spring wheat seeding at Fort Ellis (2016). It is important to note that there were no differences in soil water among treatments following the over-winter recharge period with one minor exception. Fallow had 4 mm greater water than the average of all cover crop treatments (p = 0.02) in the 0-0.3 m depth. Soil NO₃-N trended differently among treatments at the 0-0.3 m depth (p = 0.06) and did differ among treatments at the 0.31-0.6 m (p <0.01) and 0.061-0.9 m (p = 0.02) depths. Fallow treatments had an average of 79% more soil NO₃-N f than all other treatments. Cool-season treatments had an average of 36% more soil NO₃-N than warm-season treatments prior to spring wheat seeding in 2016.

One of the potential positives of grazing on cropland is that livestock deposit phosphorous (P) rich waste wherever they graze. An omnibus ANOVA among mean treatment P₂O₅ levels in 2016 (Table 13) showed no differences (p = 0.24). However, contrasts showed that the fallow treatment had an average of 14% less soil P₂O₅ than did all other treatments (p = 0.03). Without subsequent crop year data, it is difficult to make judgements about how soil P different among cover crop treatments in this study. Further long-term analysis of soil P₂O₅ levels in grazed versus ungrazed cover cropping systems would provide valuable information regarding soil P₂O₅ dynamics in such systems.

Soil microbial biomass measured prior to spring wheat seeding at Fort Ellis (2016) showed no differences among treatments (p = 0.97) or groups of treatments (data not shown in this report). A lack of treatment effect on soil microbial biomass may be the result of a short cover crop growing season and a lack of subsequent rotation years. Other studies have shown positive correlation between soil microbial biomass and cover cropping (Acosta-Martinez et al., 2011; Biederbeck et al., 2005; Housman, 2016; O’Dea, 2011); however, all of these studies were conducted for a duration of 4 years or more.

Soil enzyme activity was less under fallow than the average of all cover crop treatments for acid (p <0.01) and alkaline (p = 0.04) phosphate and β-glucosidase (p = 0.05) enzyme activity prior to spring wheat planting at Fort Ellis (Table 14). On average, fallow treatments had 35%, 23%, and 36% less acid and alkaline phosphatase and β-glucosidase soil enzyme activity than did other treatments, respectively. This effect is likely due to the absence of plant growth in 2015 in the fallow treatment and subsequent lack of soil inputs (i.e. cover crop litter) which increase soil enzyme activity (Acosta-Martinez et al., 2004). Further research demonstrating the long-term effects of cover cropping versus fallowing on soil enzyme activity may provide producers with more data regarding the implications of cover cropping for on soil quality.

 Interestingly, sprayed and grazed treatments also differed with regard to acid phosphatase (p <0.01). The mean of the herbicide-terminated treatments had ~25% less acid phosphatase activity than the mean of the grazed plots and the fallow treatment averaged even lower which agrees with Biederbeck et al. (2005). While these results are likely due to the presence of grazing (high P, labile animal waste deposition; Acosta-Martinez et al., 2011) it was surprising that only 24 hr of mob-grazing by sheep could cause an effect on soil 9-10 mo later. Further, long-term studies may shed more light on the long-term implications of grazing cover crops on soil enzyme activity in no-till dryland wheat systems.

Objective 3

The third objective of this study was to assess how changes in soil properties, catalyzed by grazing cover crops, affect subsequent wheat yields. At Fort Ellis, spring wheat yields did not differ with regard to the 2015 cover crop treatments. However, wheat yields differed among fertilization subplot levels (p <0.01). Wheat yields ranged from 3.28 Mg ha^-1 in the 0 kg N ha^-1 subplots to 4.06 Mg ha^-1 in the 135 kg N ha^-1 subplots. Spring wheat grain protein was 3 g kg^-1 greater after fallow compared with the average of all cover crop treatments (p = 0.01). Further, the herbicide-terminated treatment had 2 g kg^-1 greater grain protein than the grazed treatments (p = 0.03). This may have to do with N availability and changes in nutrient cycling associated with animal grazing (Assmann et al., 2014). Livestock also remove some N from grazing/cropping systems in the form of animal tissue (Hatfield et al., 2000); however, soil NO₃-N values in Table 11 do not indicate that a notable amount of N was removed from the system.

Although, cover crop treatments did not affect subsequent wheat yields, they influenced subsequent spring wheat grain protein (p = 0.04). This variation is due, in part, to the fact that fallow treatments had a mean Soil NO₃-N kg ha^-1 level 56%, 210%, and 70% greater than all other plots at the 0-0.3 m (p = 0.02), 0.31-0.61 m (p <0.01) and 0.61-0.91 m (p = 0.02) depths, respectively (Table 11). These differences in plant available NO₃ likely contributed to the difference in wheat seed protein in the fallow versus all comparison as other cover crop studies have shown deficits in NO₃-N kg ha^-1 following cover crops when compared to fallow (Housman, 2016; O’Dea, 2011).

Furthermore, contrast p-values for comparisons between groups of cover crop treatments indicate that the cool-season treatments had 57%, 47% and 6% more NO₃-N kg ha^-1 than warm-season treatments at the 0-0.3 m (p = 0.03), 0.31-0.6m (p <0.01), and 0.61-0.9 m (p <0.01) depths, respectively (Table 11). This variation is likely due to the fact that cool-season treatments had ~10% more cover crop biomass and 4 wk longer to decompose compared to warm-season treatments.

Objective 4

The fourth objective of this project was to increase local producer knowledge of cover crop mixtures, termination methods, and potential benefits for soil quality as well as provide local producers with information regarding the potential benefits of ICLS and methods of ICLS adoption in Montana through scientific and extension publications. At this point in time, no scientific or extension publications have been produced. However, a Master’s thesis centered on this project will be completed by May of 2017 and publications will follow. Further, Dr. Emily Glunk is on this M.Sc. student committee and is the Forage Extension Specialist at MSU. Thus, she will have firsthand knowledge of these results to use in her extension programming.Tables 4-15; References

Impacts and Contributions/Outcomes

Impacts and Contributions/Outcomes

Publications/Outreach

1. Presentations, Lectures

• Walker, R.M. “Sustainable Agriculture in the Norther Great Plains.” Introduction to Environmental Sciences Course (Fall Semester), Rocky Mountain College, Billings, MT. Oct 18, 2016. Oral presentation, Q & A, ~15 people, 50 min.
• Walker, R.M. “Cover Crop Grazing: Optimal Seasonality for Soil and Livestock Benefit”. Sustainable Cropping Systems Course, Montana State University, Bozeman, MT. Feb 25, 2016. Oral presentation, Q & A, ~30 people, 50 min.
• Walker, R.M. “Sustainable Agriculture in the Norther Great Plains.” Introduction to Environmental Sciences Course (Spring Semester), Rocky Mountain College, Billings, MT. Feb 25, 2016. Oral presentation, Q & A, ~20 people, 50 min.
• Walker, R.M. “Sustainable Agriculture in the Norther Great Plains.” Introduction to Environmental Sciences Course (Fall Semester), Rocky Mountain College, Billings, MT. Nov 19, 2015. Oral presentation, Q & A, ~15 people, 50 min.
• Walker, R.M. “Cover Crop Grazing: Optimal Seasonality for Soil and Livestock Benefit”. LRES 500 Seminar Series, Montana State University, Bozeman, MT. Nov 9, 2015. Oral presentation, Q & A, ~25 people, 40 min.

    Pending

• Walker, R.M. “Cover Crop Grazing: Optimal Seasonality for Soil and Livestock Benefit.” M.S. Thesis defense, Montana State University, Bozeman, MT. Oral Presentation. ~25 people, 1 hr.

2. Publications (Pending)

• Thesis
• Montana State University Extension guide to integrated crop-livestock producers.

- Planned guide for producers, which this study will contribute data to.

Farmer Adoption

Cover crop acres will likely increase across Montana. In 2016, there were 5,200 ha (13,000 ac) in Montana, which has been static the last three years (FSA, 2016). However, from 2014 to2016, annual dryland cover crops used as forage or grazing increased by 33,000 ha (81,000 ac (FSA, 2016). This increase in cover crop used as forage or grazing indicates the need for further understanding of how grazed/hayed cover crops affect edaphic and farm economics. Further long-term research across multiple regions of Montana may provide researchers, government agencies, and area farmers with valuable data regarding the use of cover crops as forage/graze.

Areas Needing Additional Study

The inferences of this study were limited by its short duration. In order to understand how cool- and warm-season cover crop mixtures in tandem with grazing cover crop mixtures affects biophysical properties and subsequent wheat yields, more long-term analyses should be conducted. Specifically, the long-term effects of cover crop mixtures soil N economy, soil P economy, and soil enzyme economy were not disclosed by this study while short-term trends imply the need for further study. 

Cover crops performance as a forage also requires further, long-term analysis. While this study showed that Apr/May-planted cool-season cover crop mixtures achieve adequate levels of biomass production, June-planted warm-season cover crop mixtures did not. Further exploration of warm-season cover crop mixture planting dates and mixed cool- and warm-season containing mixtures may provide valuable information regarding the use of cover crops as a forage in the NGP.