Cover Crop Grazing: Optimal Seasonality for Soil and Livestock Benefit

Final report for GW16-053

Project Type: Graduate Student
Funds awarded in 2016: $25,000.00
Projected End Date: 07/31/2017
Grant Recipient: Montana State University
Region: Western
State: Montana
Graduate Student:
Major Professor:
Dr. Perry Miller
Montana State University
Expand All

Project Information

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 were terminated with herbicide (i.e. ‘brown manures’), grazing, or haying, and compared with chem-fallow. Based on equal growing degree days, cool-season biomass production (4.5 Mg/ha) was <10% greater (p = 0.03) than warm-season biomass at Fort Ellis (2015), but at the north Gallatin Valley (NGV) location in 2016, cool-season biomass (2.4 Mg/ha) 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, especially in years with abnormally low June rain. Forage quality of the warm-season mixes were generally superior to cool-season cover crop mixes but forage quantity is of paramount interest in most Montana grazing systems.
When measured after termination at both sites, soil under cover crops contained 4-8 mm (0.15-0.3 in) less soil water and 24-30 kg/ha (21-27 lb/ac) less Nitrate-N than chem-fallow (P<0.01). When Fort Ellis was resampled Apr 13, 2016, prior to spring wheat seeding, soil water no longer differed among treatments, but soil Nitrate-N differences remained the same. Although differences in soil water and nitrate were detected between warm-season and cool-season cover crops, the differences were small. Some soil measures showed that retaining cover crop biomass on plots produced more biologically active soil compared with removal of crop biomass via 24 hr of mob-grazing. However, at both sites, acid phosphatase enzyme activity was 29% greater on graze-terminated vs spray-terminated cover crop treatments, averaged across cool- and warm-season crop mixtures when measured 9-10 months later prior to seeding the spring wheat response crop. Enzymatic activity was reduced on the chem fallow control plots at the Fort Ellis site, but not at the site in the northern Gallatin Valley. Cover crop treatments did not affect a spring wheat response crop differently at Fort Ellis, while the fallow control had slightly greater wheat grain yield and protein. Wheat data from the NGV site were not obligated within the time frame of this study but will be reported when those data are processed and analyzed, no later than March 1, 2018.

Project Objectives:

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

Objective 4. To increase local producer knowledge of cover crop mixtures performance as forages/graze and termination methods and potential benefits for soil quality.

Objective 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 2015-16 study site was the Montana State University – Fort Ellis Research Farm (N 45.667°, W 110.978°) located near Bozeman, MT. The site that was planted in barley during the 2014 growing season 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 ~500 mm (19.7 inches). Fort Ellis was planted in cover crops in 2015, followed by a spring wheat response crop in in 2016 (cv. Duclair). In 2016, a second site in northern Gallatin Valley, MT (NGV) was established in partnership with local farmer, Jason Camp. The site was sown to winter wheat during the 2015 season and hayed alfalfa for several years prior. This field site experiences less annual rainfall (~360 mm) with a predominant soil type of Amsterdam silt loam (Tables 1 & 2).

 

Table 1. Monthly precipitation and cover crop GDD (Tbase = 0 °C) at Fort Ellis and NGV, MT. Growing season is Apr–July. GDD calculated from day after seeding to day of termination for each cover crop mixture. Long-term average (LTA) calculated from 1981-2010, Western Regional Climate Center. WRCC station number and distance to field site are listed below site name.

 

Fort Ellis

NGV

(241044, 5.5 km)

(240622, 14.5 km)

 

2015

2016

LTA

2016        2017

LTA

Annual Precip. (mm)

450

472

501

336        N/A

357

Annual Temp. (°C)

8.2

7.8

7.1

6.9        N/A

6.0

Growing Season Rain (mm)

214

166

254

155        166

193

Cover Crop Mixture

Cool

Warm

Cool

Warm

GDD (°C)

902

944

862

961

 

Table 2. Pre-planting soil characterizationz of Fort Ellis and NGV, MT.

 

Fort Ellis

(2015)

NGV

(2016)

Location

45.667°, -110.978°

45.904°, -111.154°

Elevation (m)

1493

1432

Soil Texture

Silt loam

Silt loam

pH

6.5

5.9

Soil Organic Matter (%)

5.3

2.6

Nitrate (mg kg-1)

9.1

4.8

Olsen P (mg kg-1)

56

39

Sample Date

24 Apr. 2015

6 May 2016

Previous crop

Spring barley

Winter wheat

z All samples analyzed by AgVise Laboratories, Northwood, ND of samples from the 0 to 15 cm depth.

 

Study Design The experimental design was a randomized complete block consisting of six cover crop/termination treatments (mainplot: 15.2 m x 7.6 m) with a split plot arrangement for response-year N fertizlizer treatments, with 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 miliaceum 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 (Raphanus sativus L. sp.) was the brassica used in both the cool-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 diameter tap root). Cover crops species were seeded in the same row (spacing: 30 cm) to a depth of 2.5 cm with a low-disturbance no-till 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 m-2 with individual cover crop species added to a mixture at a target seed rate of 40 m-2. 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; Tbase = 0°C) approximately equal to the cool-season mixture.

Table 3. Agronomic management for cover crop mixtures and spring wheat at Fort Ellis and NGV, MT.  

Event

2015

2016

2016

2017

 

——– Fort Ellis ——-

——– NGV ——-

Pre-seed soil sample

Apr 24

Apr 12

May 6

May 9

Cool-season crop seeding

Apr 29

N/A

May 5

N/A

Cool-season crop stand counts

May 28

N/A

June 1

N/A

Cool-season crop pre-termination biomass

June30

N/A

July 4

N/A

Cool-season crop termination

July 1

N/A

July 5

N/A

Cool-season crop post-termination biomass

July 2

N/A

July 6

N/A

Supplemental spraying (grazed plots only)

Aug 3

N/A

Aug 11

N/A

Soil sample date (NO3 and H2O)

July 10

N/A

July 12

N/A

Warm-season crop seeding

June 15

N/A

June 20

N/A

Warm-season crop stand counts

July 7

N/A

July 17

N/A

Warm-season crop pre-termination biomass

Aug 3

N/A

Aug 10

N/A

Warm-season crop termination

Aug 4

N/A

Aug 10

N/A

Warm-season crop post-termination biomass

Aug 5

N/A

Aug 11

N/A

Soil sample date (NO3 and H2O)

Aug 17

N/A

Aug 18

N/A

Spring wheat seeding

N/A

Apr 12

N/A

May 11

Spring wheat stand counts

N/A

May 10

N/A

N/A

Spring wheat biomass at anthesis

N/A

July 6

N/A

N/A

Spring wheat harvest

N/A

Aug 17

N/A

Sep 7

First frost date (0 °C)*

Oct 3

N/A

Oct 6

N/A

Warm-season radish termination (-4 °C)*

Nov 6

N/A

Oct 11

N/A

*Data from Western Regional Climate center station (241044).

 

 

Cover crop treatments are described in Table 4.

Chemical-fallow (fallow), served as the control treatment, representing a common grower standard practice in Montana. Lambs (Ovis aries) were used to ‘mob-graze’ the grazed cover crop treatments. However, after grazing, the cool-graze treatment was sprayed within a month of grazing to ensure termination of plant growth and 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 incurred unusually late first fall frosts (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 contrasted cool-graze and warm-graze for plant biomass removal. In the warm-hay, cover crops were swathed and then killed by frost in order to isolate the effect of cover crop biomass removal with livestock absent. However, in year-2, due to very limited biomass growth, warm-hay was swathed and the biomass was left on the plots to simulate mowing, since it would have been very difficult to remove scant cut biomass without excess soil surface disturbance.

 

Table 4.  Study treatments, termination methods and cover crop mixtures at Fort Ellis (2015) and NGV (2016), MT.

Treatment

Termination Method

Cover Crop Mixture

1) Chemical-Fallow

(fallow)

None

None

2) Cool-season – graze

 (cool graze)

grazed by lambs and sprayed with Glyphosate

radish, pea and oat

3) Cool-season – spray out

(cool spray)

sprayed with glyphosate

radish, pea and oat

4) Warm-season – graze

(warm graze)

grazed by lambs and frost kill

radish, soybean and sorghum/millet*

5) Warm-season – spray out

(warm spray)

Sprayed with Glyphosate and frost kill

radish, soybean and sorghum/ millet*

6) Warm-season – swath

(warm hay)**

swathed and frost kill

radish, soybean and sorghum/ millet*

*Proso millet was substituted for sorghum in the warm-season mixture in year-2 as sorghum can produce toxic levels of prussic acid (hydrocyanic acid) and poison livestock (Sher et al., 2012).

** In year-2, due to low biomass growth, treatment 6 was swathed and the biomass was left on the plots to simulate mowing.

In year-2, all main plots were sown to spring wheat (cv. Duclair) with a low-disturbance no-till disk drill to a depth of 2.5 cm, perpendicular to the drill direction used for year-1 cover crop seeding. Nitrogen fertilizer treatments subplots were banded >5 cm below and to the side of the seed furrow at rates of 0, 67.5, and 135 kg N ha-1 (0, 60, and 120 lb n ac-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 border to avoid edge effects. Crop management treatments were implemented on the same day, within cool- and warm-season growth regimes, respectively. Above-ground cover crop biomass for all plots was sampled in the same areas used for seedling counts by hand-harvesting plant biomass to the soil surface within 24 hr of termination. Grazed and swathed plots, were resampled similarly within 48 hr after termination to measure post-grazing and post-haying residual biomass. All samples were dried at 50°C prior to obtaining dry weights. For warm-season cover crop treatments, enlarged radish roots below soil surface were dug, cleaned, 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 subsamples were taken from all grazed and swathed treatments pre- and post-termination (including cool-season re-growth prior to glyphosate application). Dried 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 To test for grazing compaction, soil penetration resistance 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 to planting cover crops, after cover crop termination, and prior to wheat seeding the following spring to determine overwinter attenuation of post-termination soil water differences. Soils were weighed fresh (or frozen) from the field, and after being placed in an oven at 50oC for 72 hr to measure 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, a 5-g subsample 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 separately 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, a 1.25-g subsample 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 soil cores to a 15-cm depth 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 concentration, 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 cellobiose from cellulose), β-Glucosaminidase (EC 3.1.2.52; cleaves N-acetyl glucosamine from chitin), and acid and alkaline phosphatases (EC 3.1.3.1, EC 3.1.3.2; cleaves phosphates from organic phosphorus compounds). One gram of 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 At Fort Ellis, 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 to obtain plant dry matter. At both sites, 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. 

Cooperators

Click linked name(s) to expand
  • Dr. Cathy Zabinski (Educator and Researcher)
  • Dr. Emily Glunk (Educator and Researcher)

Research

Materials and methods:

Site Characterization
The 2015-16 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 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 ~500 mm (19.7 inches). Fort Ellis was planted in cover crops in 2015, followed by a spring wheat response crop in in 2016 (cv. Duclair). In 2016, a second site in northern Gallatin Valley, MT (NGV) was established in partnership with local farmer, Jason Camp. The site was sown to winter wheat during the 2015 season and hayed alfalfa for several years prior. This field site experiences less annual rainfall (~360 mm) with a predominant soil type of Amsterdam silt loam (Tables 1 & 2).

 

Table 1. Monthly precipitation and cover crop GDD (Tbase = 0 °C) at Fort Ellis and NGV, MT. Growing season is Apr–July. GDD calculated from day after seeding to day of termination for each cover crop mixture. Long-term average (LTA) calculated from 1981-2010, Western Regional Climate Center. WRCC station number and distance to field site are listed below site name.

 

Fort Ellis

NGV

(241044, 5.5 km)

(240622, 14.5 km)

 

2015

2016

LTA

2016        2017

LTA

Annual Precip. (mm)

450

472

501

336        N/A

357

Annual Temp. (°C)

8.2

7.8

7.1

6.9        N/A

6.0

Growing Season Rain (mm)

214

166

254

155        166

193

Cover Crop Mixture

Cool

Warm

Cool

Warm

GDD (°C)

902

944

862

961

 

 

Table 2. Pre-planting soil characterizationz of Fort Ellis and NGV, MT.

 

Fort Ellis

(2015)

NGV

(2016)

Location

45.667°, -110.978°

45.904°, -111.154°

Elevation (m)

1493

1432

Soil Texture

Silt loam

Silt loam

pH

6.5

5.9

Soil Organic Matter (%)

5.3

2.6

Nitrate (mg kg-1)

9.1

4.8

Olsen P (mg kg-1)

56

39

Sample Date

24 Apr. 2015

6 May 2016

Previous crop

Spring barley

Winter wheat

z All samples analyzed by AgVise Laboratories, Northwood, ND of samples from the 0 to 15 cm depth.

Study Design
The experimental design was a randomized complete block consisting of six cover crop/termination treatments (mainplot: 15.2 m x 7.6 m) with a split plot arrangement for response-year N fertizlizer treatments, with 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 miliaceum 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 (Raphanus sativus L. sp.) was the brassica used in both the cool-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 diameter tap root). Cover crops species were seeded in the same row (spacing: 30 cm) to a depth of 2.5 cm with a low-disturbance no-till 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 m-2 with individual cover crop species added to a mixture at a target seed rate of 40 m-2. 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; Tbase = 0°C) approximately equal to the cool-season mixture.

Table 3. Agronomic management for cover crop mixtures and spring wheat at Fort Ellis and NGV, MT.  

Event

2015

2016

2016

2017

 

——– Fort Ellis ——-

——– NGV ——-

Pre-seed soil sample

Apr 24

Apr 12

May 6

May 9

Cool-season crop seeding

Apr 29

N/A

May 5

N/A

Cool-season crop stand counts

May 28

N/A

June 1

N/A

Cool-season crop pre-termination biomass

June30

N/A

July 4

N/A

Cool-season crop termination

July 1

N/A

July 5

N/A

Cool-season crop post-termination biomass

July 2

N/A

July 6

N/A

Supplemental spraying (grazed plots only)

Aug 3

N/A

Aug 11

N/A

Soil sample date (NO3 and H2O)

July 10

N/A

July 12

N/A

Warm-season crop seeding

June 15

N/A

June 20

N/A

Warm-season crop stand counts

July 7

N/A

July 17

N/A

Warm-season crop pre-termination biomass

Aug 3

N/A

Aug 10

N/A

Warm-season crop termination

Aug 4

N/A

Aug 10

N/A

Warm-season crop post-termination biomass

Aug 5

N/A

Aug 11

N/A

Soil sample date (NO3 and H2O)

Aug 17

N/A

Aug 18

N/A

Spring wheat seeding

N/A

Apr 12

N/A

May 11

Spring wheat stand counts

N/A

May 10

N/A

N/A

Spring wheat biomass at anthesis

N/A

July 6

N/A

N/A

Spring wheat harvest

N/A

Aug 17

N/A

Sep 7

First frost date (0 °C)*

Oct 3

N/A

Oct 6

N/A

Warm-season radish termination (-4 °C)*

Nov 6

N/A

Oct 11

N/A

*Data from Western Regional Climate center station (241044).

Cover crop treatments are described in Table 4. Chemical-fallow (fallow), served as the control treatment, representing a common grower standard practice in Montana. Lambs (Ovis aries) were used to ‘mob-graze’ the grazed cover crop treatments. However, after grazing, the cool-graze treatment was sprayed within a month of grazing to ensure termination of plant growth and 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 incurred unusually late first fall frosts (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 contrasted cool-graze and warm-graze for plant biomass removal. In the warm-hay, cover crops were swathed and then killed by frost in order to isolate the effect of cover crop biomass removal with livestock absent. However, in year-2, due to very limited biomass growth, warm-hay was swathed and the biomass was left on the plots to simulate mowing, since it would have been very difficult to remove scant cut biomass without excess soil surface disturbance.

Table 4.  Study treatments, termination methods and cover crop mixtures at Fort Ellis (2015) and NGV (2016), MT.

Treatment

Termination Method

Cover Crop Mixture

1) Chemical-Fallow

(fallow)

None

None

2) Cool-season – graze

 (cool graze)

grazed by lambs and sprayed with Glyphosate

radish, pea and oat

3) Cool-season – spray out

(cool spray)

sprayed with glyphosate

radish, pea and oat

4) Warm-season – graze

(warm graze)

grazed by lambs and frost kill

radish, soybean and sorghum/millet*

5) Warm-season – spray out

(warm spray)

Sprayed with Glyphosate and frost kill

radish, soybean and sorghum/ millet*

6) Warm-season – swath

(warm hay)**

swathed and frost kill

radish, soybean and sorghum/ millet*

*Proso millet was substituted for sorghum in the warm-season mixture in year-2 as sorghum can produce toxic levels of prussic acid (hydrocyanic acid) and poison livestock (Sher et al., 2012).

** In year-2, due to low biomass growth, treatment 6 was swathed and the biomass was left on the plots to simulate mowing.

In year-2, all main plots were sown to spring wheat (cv. Duclair) with a low-disturbance no-till disk drill to a depth of 2.5 cm, perpendicular to the drill direction used for year-1 cover crop seeding. Nitrogen fertilizer treatments subplots were banded >5 cm below and to the side of the seed furrow at rates of 0, 67.5, and 135 kg N ha-1 (0, 60, and 120 lb n ac-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 border to avoid edge effects. Crop management treatments were implemented on the same day, within cool- and warm-season growth regimes, respectively. Above-ground cover crop biomass for all plots was sampled in the same areas used for seedling counts by hand-harvesting plant biomass to the soil surface within 24 hr of termination. Grazed and swathed plots, were resampled similarly within 48 hr after termination to measure post-grazing and post-haying residual biomass. All samples were dried at 50°C prior to obtaining dry weights. For warm-season cover crop treatments, enlarged radish roots below soil surface were dug, cleaned, 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 subsamples were taken from all grazed and swathed treatments pre- and post-termination (including cool-season re-growth prior to glyphosate application). Dried 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
To test for grazing compaction, soil penetration resistance 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 to planting cover crops, after cover crop termination, and prior to wheat seeding the following spring to determine overwinter attenuation of post-termination soil water differences. Soils were weighed fresh (or frozen) from the field, and after being placed in an oven at 50oC for 72 hr to measure 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, a 5-g subsample 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 separately 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, a 1.25-g subsample 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 soil cores to a 15-cm depth 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 concentration, 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 cellobiose from cellulose), β-Glucosaminidase (EC 3.1.2.52; cleaves N-acetyl glucosamine from chitin), and acid and alkaline phosphatases (EC 3.1.3.1, EC 3.1.3.2; cleaves phosphates from organic phosphorus compounds). One gram of 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
At Fort Ellis, 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 to obtain plant dry matter. At both sites, 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.

Research results and discussion:

Objective 1

The first objective of this study was to evaluate cool- and warm-season annual cover crop mixtures for forage productivity in a dryland wheat-cover crop systems. In the NGP, forage quality, and especially quantity, affect the monetary value of hay and pasture. Crop biomass at termination 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 despite cool-season treatments receiving 95 mm of rain between seeding and termination while the warm season treatments received only 21 mm of rain between seeding and termination. Cool-season biomass was ~170% greater than warm-season biomass (p <0.01) in 2016 when cool-season treatments received 96 mm of rain between seeding and termination, and warm-season treatments received only 6 mm. June 2015 and June 2016 were abnormally dry; the driest June’s on record since 1985 at Fort Ellis and 2003 at the NGV, respectively. Such abnormally dry Junes may not accurately reflect biomass production potential from warm-season crops.

These data imply that the spring-centric precipitation patterns of the NGP may not be conducive to warm-season cover crop biomass production, and may be best used as a strategy when sufficient June rain has been received, or is forecast to occur. 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.

Table 5. Cover crop treatment biomass yield and quality at Ft. Ellis, MT and NGV, MT

 

Treatment

Pre-termination Biomass

Post-termination Biomass

Pre-termination C:N ratio*

 

2015

2016

2015

2016

2015

2016

             

P-values

   0.16

<0.01

<0.01

0.43

0.10

<0.01

 

—— Mg ha-1 ——

——– Mg ha-1 ——–

 

Cool Graze

4.65

2.59

1.41

0.22

18.3

17.8

Cool Spray

4.33

2.32

N/A

N/A

N/A

N/A

Warm Graze

4.04

1.10

1.43

0.16

15.0

12.0

Warm Spray

4.22

1.02

N/A

N/A

N/A

N/A

Warm Hay

4.09

1.14

0.28

0.27

14.8

12.8

Contrasts

————————————- P-values ———————————-

Cool v. Warm

0.03

<0.01

N/A

N/A

0.04

<0.01

Spray v. Graze

0.70

0.20

N/A

N/A

N/A

N/A

WG v. WH

0.48

0.46

<0.01

0.29

N/A

N/A

CG = cool graze, WG = warm graze, and WH = warm hay.

*All cover crop species combined per plot.

Results come from an omnibus ANOVA.

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 mixture than in the cool-season mixture in both 2015 (p <0.01) and 2016 (p <0.01). The same contrast, cool v. warm, also showed that ADF was lower across warm-season treatments than in the cool-season treatments 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).

Table 6. Treatment P values and means of cover crop mixtures from grazed and hayed plots at Fort Ellis (2015) and NGV (2016), MT. Dry matter (DM), crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), total digestible nutrients (TDN), and Relative Feed Value (RFV). 

Treatment

DM

CP

ADF

NDF

TDN

RFV

DM

CP

ADF

NDF

TDN

RFV

p-value

0.63

0.02

0.02

0.01

0.02

0.02

0.26

<0.01

0.02

0.41

0.02

0.24

 

————————— 2015 ———————–

————————— 2016 ————————-

CG

907

158

426

526

540

  99

901

155

351

475

625

121

WG

908

229

370

488

604

115

889

224

274

475

711

149

WH

914

185

370

561

604

100

899

212

303

430

680

130

LSDtreat

NS

  41

  37

  39

  42

  11

NS

  28

  49

NS

  54

NS

Contrast

—————————————————— p-values ——————————————————-

Warm v. Cool

0.58

<0.01

<0.01

0.94

<0.01

0.07

0.31

<0.01

0.01

0.50

0.01

0.20

CG = cool graze, WG = warm graze, and WH = warm hay

RFV Index = DDM x DMI / 1.29, where:

         DDM = Digestible Dry Matter = 88.9 – (0.779 x %ADF) on a dry matter basis

         DMI = Dry Matter Intake = 120 / %NDF on a dry matter basis

Objective 2

The second objective of this study was to investigate how grazing cover crop mixtures as a termination method, with concomitant biomass removal, affects soil biochemical properties in comparison to using herbicide for crop termination, where crop biomass is retained on the plots. A major 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 preceeding 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. Since soil moisture differences skew soil penetrometer results, these data may not be informative. Analysis of soil bulk density data prior to seeding spring wheat at Fort Ellis in 2016 (Table 8) showed no sign of compaction at any depth, furthering the conclusion that mob-grazing (218 sheep ac-1) for 24 hr did not compact soil importantly.

Table 7. Soil penetration resistance measured Apr 13 2016 prior to wheat planting, following 2015 cover crop treatments, Fort Ellis, MT

 

Depth (cm)

Treatment

0 – 7.5

7.5 – 15

15 – 22.5

22.5 – 30

p-values

0.15

<0.01

<0.01

0.26

 

—————————kg cm-1———————–

Fallow

7.2

  8.2

  7.9

8.0

Cool Graze

7.0

10.6

10.9

9.3

Cool Spray

8.3

10.0

  9.5

9.4

Warm Graze

6.3

  8.9

  9.1

9.1

Warm Spray

6.3

  9.4

  8.9

8.1

Warm Hay

7.5

  8.6

  7.8

8.3

LSDtreat

NS

  1.1

  1.5

NS

Contrast

———————— p-values———————-

Fallow v. All

0.33

<0.01

0.03

0.17

Cool v. Warm

0.10

<0.01

<0.01

0.09

Spray v. Graze

0.28

0.94

0.13

0.41

 

Table 8. Soil bulk density measured Apr 13 2016 prior to wheat planting, following 2015 cover crop treatments, Fort Ellis, MT.

 

Depth (cm)

Treatment

0 – 0.3

0.31 – 0.6

0.61 – 0.9

p-values

0.51

0.99

0.44

 

—————– kg cm3 -1 —————–

Fallow

1.3

1.3

1.3

Cool Graze

1.3

1.4

1.3

Cool Spray

1.2

1.4

1.2

Warm Graze

1.3

1.3

1.3

Warm Spray

1.3

1.4

1.3

Warm Hay

1.3

1.4

1.2

LSDtreat

NS

NS

NS

Contrasts

—————— p-values—————–

Fallow v. All

0.13

0.72

0.37

Cool v. Warm

0.34

0.86

0.66

Spray v. Graze

0.40

0.86

0.14

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). In 2105, at Fort Ellis, fallow treatments measured after warm-season cover crop termination had an average of 8 mm (0.3 in) more soil water than all other treatments in 2015, and 4 mm (0.15 in) in 2016. Cool-season treatments used very slightly more water (i.e. 1-2 mm) than warm-season treatments in 2015, but this difference was not so clear in 2016. Soil NO3-N levels following cover crop termination did not differ among cover crop treatments but fallow averaged 30 and 24 kg ha-1 (27 and 21 lb ac-1) greater N than the cover crop treatments in 2015 and 2016, respectively. When re-measured in the spring prior to wheat planting at Fort Ellis, soil water differences among treatments had disappeared, and soil nitrate-N differences existed only below 0.3 m (1 ft). Fallow still contained 32 kg ha-1 (29 lb ac-1) greater N than the cover crop treatments, and cool-season crop treatments held 8 kg ha-1 (7 lb ac-1) greater nitrate-N than the warm-season crop treatments, positioned in the 0.3-0.6 m soil depth. The following pattern was observed: fallow >> cool-season > warm-season, which may signify more cover crop litter breakdown in cool-season treatments. Other studies (Biederbeck et al., 1996; Miller et al., 2006; van Kessel and Hartney, 2000) have noted similar losses of soil NO3-N following cover cropping. This is likely the result of N immobilization by 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.

Table 10. Soil Nitrate-N (NO3-N) measured after cover crop termination, at Fort Ellis, MT, July 10, 2015, and NGV, MT, July 12, 2016.  

 

Fort Ellis 2015

NGV 2016

Treatment

0 to 0.3 m

0.3 to 0.6 m

0.6 to 0.9 m

Total

0 to 0.3 m

0.3 to 0.6 m

0.6 to 0.9 m

Total

p-value

<0.01

<0.01

0.60

 

<0.01

<0.01

<0.01

 

 

—————————————————– kg ha-1 ————————————————————-

Fallow (Cool)

31

12

10

53

24

7

11

42

Fallow (Warm)

23

13

12

48

30

12

12

54

Cool Graze

8

3

6

17

7

3

18

28

Cool Spray

6

2

6

14

10

3

5

18

Warm Graze

13

2

10

25

12

3

6

21

Warm Spray

17

4

10

31

14

5

8

27

Warm Hay

7

3

6

16

12

5

8

25

LSD

10

4

NS

 

9

4

11

 

 Contrasts

    ———————————————— p –values ————————————————–

Fallow v. All

<0.01

<0.01

0.64

 

<0.01

0.19

0.67

 

Cool v. Warm

0.01

<0.01

0.33

 

0.08

0.07

0.24

 

Spray v. Graze

<0.01

<0.01

0.22

 

<0.01

<0.01

0.50

 

 

Table 11. Soil water (mm water equivalence) and nitrate (kg ha-1), measured on Apr 12, 2016, prior to planting wheat and following 2015 cover crop treatments, Fort Ellis, MT.

 

Soil Water

Soil NO3-N

Treatment

0 to 0.3 m

0.31 to 0.6 m

0.61 to 0.9 m

0 to 0.3 m

0.31 to 0.6 m

0.61 to 0.9 m

p-values

0.09

0.54

0.82

0.06

<0.01

0.02

 

—————-Soil Water mm-1 —————-

————– Soil NO3-N kg ha-1 ————–

Fallow

94

87

80

30

39

28

Cool Graze

87

85

78

25

24

18

Cool Spray

90

84

78

24

22

16

Warm Graze

90

86

77

18

14

12

Warm Spray

91

84

80

13

16

21

Warm Hay

91

83

80

16

17

15

LSDTreat

NS

NS

NS

NS

  4

  9

Contrasts

———————————————- p-values———————————————–

Fallow v. All

0.02

0.17

0.57

0.02

<0.01

<0.01

Cool v. Warm

0.13

0.93

0.67

0.03

<0.01

<0.01

Spray v. Graze

0.19

0.36

0.45

0.40

0.87

0.87

Potentially mineralizable nitrogen (PMN) trended differently (p = 0.07) among treatments prior to spring wheat seeding at Fort Ellis in 2016, but not at NGV in 2017 (Table 12). Spray-terminated treatments had 63% greater PMN values than graze-terminated treatments at Fort Ellis. 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 plant biomass 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. Similar differences were not observed at the NGV site.

One of the potential positives of grazing on cropland is that livestock deposit phosphorous (P) rich waste while grazing. An omnibus ANOVA among mean treatment P2O5 levels in 2016 (Table 13) showed no differences between grazed and ungrazed treatments in either year. However, inexplicably the fallow treatment had an average of 14% less soil P2O5 than did all other treatments (p = 0.03). No P fertilizer was applied during cover crop seeding, and the seed drill was run through the fallow plot without applying seed when cool-season crops were sown, to ensure equal levels of soil surface disturbance.

Table 12. Soil PMN (kg NH4 ha-1) measured on fresh soil sampled Apr 12, 2016 and May 9, 2017, prior to wheat planting at Fort Ellis and NGV, MT, respectively. ANVOA showed treatment trend (p = 0.07) at Fort Ellis but no treatment effect at NGV (p = 0.18).

Treatment

Fallow

Cool Graze

Cool Spray

Warm Graze

Warm Spray

Warm Hay

Fort Ellis (2016)

28.6

26.5

42.9

24.6

40.7

20.8

NGV (2017)

  9.2

  9.5

  8.8

  9.9

10.5

10.4

 

Contrast p-values

Fallow v. All

Cool v. Warm

Spray v. Graze

Fort Ellis (2016)

0.68

0.25

0.01

NGV (2017)

0.73

0.46

0.97

 

Table 13. Pre-planting soil phosphate (kg P2O5 ha-1) Apr 13, 2016 at Fort Ellis and (ppm) May 9, 2017, at NGV, measured immediately prior to wheat seeding to test cover crop treatment effects.

Treatment

Fallow

Cool Graze

Cool Spray

Warm Graze

Warm Spray

Warm Hay

Fort Ellis (2016)

121

136

139

143

134

134

NGV (2017)

41.4

41.2

40.8

39.6

43.2

40.2

Contrast

Fallow v. All

Cool v. Warm

Spray v. Graze

Fort Ellis (2016)

0.03

0.87

0.66

NGV (2017)

0.87

NS

0.38

Soil microbial biomass measured prior to spring wheat seeding showed no differences among treatments (p = 0.97) at Fort Ellis (2016) or (p = 0.18) at NGV (2017) (data not shown). 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 2016 spring wheat planting at Fort Ellis, but similar effects were not found at NGV in 2017 (Table 14). At Fort Ellis, fallow treatments averaged 35%, 23%, and 36% less acid and alkaline phosphatase and β-glucosidase soil enzyme activity than cropped treatments, respectively. This effect is likely due to the absence of plant growth in 2015 in the fallow treatment and subsequent lack of biomass inputs which increase soil enzyme activity (Acosta-Martinez et al., 2004).
More interestingly, sprayed and grazed treatments differed with regard to acid phosphatase (p <0.01) at Fort Ellis, and a similar trend was noted at NGV (p=0.16). The mean of the spray-terminated treatments had ~29% less acid phosphatase activity than the mean of the grazed plots at both sites, 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 enzymes when measured 9-10 mo later. Long-term studies may shed more light on the implications of grazing cover crops on soil enzyme activity in no-till dryland wheat systems.

Table 14. Soil enzyme activity, measured Apr 13, 2016 and May 9, 2017, prior to wheat planting, at Fort Ellis, and NGV, MT, respectively. Mean treatment values of soil enzyme activity represent mg of p-nitrophenol (PN) produced per kg soil per hour. Only phosphatase was measured at NGV (raw ppm values).

 

Treatment

β-Glucosaminidase

 

Acid phosphatase

Alkaline phosphatase

 

β-Glucosidase

   

2016

2017

2016

2017

 

p-values

0.21

<0.01

0.37

0.32

0.20

0.11

   

————————— mg PN kg-1 soil h-1 —————————

Fallow

154

215

  9.3

224

  7.5

139

Cool Graze

204

377

12.1

291

10.9

209

Cool Spray

180

287

  9.9

266

  7.7

155

Warm Graze

223

363

15.2

283

  7.4

193

Warm Spray

174

287

11.3

262

11.1

218

Warm Hay

164

235

13.6

279

13.0

168

LSD

NS

84.3

NS

NS

NS

NS

Contrasts

 

———————————– p-values ——————————

Fallow v.

All

0.14

<0.01

0.20

0.04

0.23

0.05

Cool v. Warm

0.79

0.17

0.23

0.85

0.49

0.57

Spray v. Graze

0.09

<0.01

0.16

0.29

0.89

0.51

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.

Table 15. Means for cover crop treatment effects on subsequent spring wheat at three N fertilizer rates on spring wheat at Fort Ellis, MT 2016.

Source of variation*

Wheat Yield

Wheat Seed Protein

 

————– p-values ————

Treatment

0.32

0.04

Block

<0.01

<0.01

Fertilizer

<0.01

<0.01

Treatment x Fertilizer

0.69

0.67

Treatment

—- Mg ha-1 —-

—– g kg-1 —-

Fallow

3.9

137

Cool Graze

3.7

132

Cool Spray

3.7

135

Warm Graze

3.7

133

Warm Spray

3.6

135

Warm Hay

3.7

133

LSDtreat.

NS

  4

Fertilizer Rate

   

    0 kg N ha-1

3.3

129

    68 kg N ha-1

3.8

134

   135 kg N ha-1

4.1

139

LSDfert.

0.2

    3

Contrasts

———— p-values ———-

Fallow v. All

0.06

0.01

Cool v. Warm

0.51

0.99

Spray v. Graze

0.32

0.03

WG v. WH

0.60

0.87

*Results come from omnibus ANOVA

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 ~ 30 kg ha-1 greater than cropping treatments (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 similar deficits in NO3-N kg ha-1 following cover crops when compared to fallow (Housman, 2016; O’Dea, 2011).

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 October 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.

References

Acosta-Martinez, V., T.M. Zobeck, Vivien Allen. 2004. Soil Microbial, Chemical and Physical Properties in Continuous Cotton and Integrated Crop-Livestock Systems. Soil Science Society of America. 68: 1875-1884.

Acosta-Martinez, V., R. Lascano, F. Calderon, J.D. Booker, T.M. Zobeck, and D.R. Upchurch. 2011. Dryland cropping systems influence the microbial biomass and enzyme activities in a semiarid sandy soil. Biology and Fertility of Soils 47: 655-667.

Assmann, T.S., I. Anghinoni, A.P. Martins, S.E.V. Gigante de Andrade Costa, D. Cecagno, F. S. Carlos, P.Cesar de Faccio Carvalho. 2014. Soil carbon and nitrogen stocks and factions in a long-term integrated crop-livestock system under no-tillage in southern Brazil. Agriculture, Ecosystems and Environment. 190: 52-59.

Bardgett, R. D., D. A. Wardle. 2010. Ch.4: Ecosystem-level significance of aboveground consumers. Aboveground-Belowground Linkages: Biotic Interactions, Ecosystem Processes, and Global Change. Oxford University Press. Oxford, U.K.

Biederbeck V.O., Bouman O.T., Campbell C.A., Bailey L.D., Winkleman G.E., 1996. Nitrogen benefits from four green-manure legumes in dryland cropping systems. Can. J. Plant Sci. 76, 307-315.

Biederbeck, V.O., R.P. Zentner and C.A. Campbell. 2005. Soil microbial populations and activities as influenced by legume green fallow in a semiarid climate. Soil Biology and Biochemistry 37:1775-1784.
Dick, R.(ed.). 2011. Methods of Soil Enzymology. SSSA Book Ser. 9. SSSA and ASA. Madison, WI.

Collins, M. 1988. Composition and fiber digestion in morphological components of an alfalfa-timothy sward. Anim. Feed Sci. Tech. 19:135–143.

Hamza, M.A., W.K. Anderson. 2005. Soil compaction in cropping systems: A review of the nature, causes and possible solutions. Soil and Tillage Research. 82: 121-145.

Hatfield, P.G., R.A. Field, J.A. Hopkins, and R. W. Kott. 2000. Palatability of wethers fed an 80% barley diet processed at different ages and of yearling wethers grazed on native range. Journal of Animal Science 78:1779-1785.

Housman, M.L. 2016. Multi-Species Cover Crops in the Northern Great Plains: An Ecological Perspective on Biodiversity and Soil Health. Master’s Thesis, Montana State University, Bozeman, MT.

Jones, C., R. Kurnick, P. Miller, K. Olson-Rutz, C. Zabinski. 2015a. 2015 Montana Cover Crop Survey Results. Montana State University, Bozeman, MT.

Jones, C., P. Miller, M. Burgess, S. Tallman, M. Housman, J. O’Dea, A. Bekkerman, and C. Zabninski. 2015b. Cover Cropping in the Semi-Arid West: Effects of Termination Timing, Species, and Mixtures on Nitrogen Uptake, Yield, Soil Quality, and Economic Return. Proceedings of the Western Nutrient Management Conference, 11:39-45.

Keeney, D. 1982. Nitrogen – availability indices. In: Methods of Soil Analysis, Part 2: Chemical and Microbiological Properties (ed. S. Segou), pp. 711–733. SSSA, Madison, WI.

Kou, S. 1996. Phosphorous. p. 869-915. In D.L. Sparks et al., (eds.). Methods of Soil Analysis, Part 3. Chemical Methods. SSSA Book Ser. 5. SSSA and ASA. Madison, WI.

McCauley, A., Jones, C., Miller, P., Burgess, M. and Zabinski, C., 2012. Nitrogen fixation by pea and lentil green manures in a semi-arid cropping system: Effect of planting and termination time. Nutr. Cycl. Agroecosys. 92: 305-314.

Miller, P.R., and J.A. Holmes. 2005. Cropping sequence effects of four broadleaf crops on four cereal crops in the northern Great Plains. Agron. J. 97:189-200.

Montana Dept. of Commerce. 2017. Census & Economic Information Center – Select Montana Agricultural Commodities Dashboard. http://ceic.mt.gov/Economics/AgricultureDashboard.aspx. Accessed [ 2 Jan 2017].

National Resource Conservation Service. 2009. Radishes: A new cover crop option. Crops and Soils: 14-17.

O’Dea, J.K. 2011. Greening summer fallow: Agronomic and edaphic implications of legumes in dryland wheat agroecosystems. Master’s Thesis, Montana State University, Bozeman, MT.

Olsen, S.R., and L.E. Sommers. 1982. Phosphorous. p. 403-430. In A.L. Page (ed.). Methods of Soil Analysis, Part 2, 2nd Ed. Agron. Mongr. No. 9 ASA and SSA. Madison, WI.

Or, D. and J.M. Wraith. 1999. Soil water content and water potential relationships. M. Summer, ed. Handbook of Soil Science. CRC Press, Boca Raton, FL. pp A53-A85.

Parham, J.A. and Deng, S.P. 2000. Detection, quantification and characterization of b-glucosaminidase activity in soil. Soil Biol. Biochem. 32, 1183–1190.

Ruess, L. and H. Ferris. 2004. Decomposition pathways and successional changes. Nematology Monographs and Perspectives. 2: 547-556.

Sainju, U.M., B.P. Singh, W.F. Whitehead. 2002. Long-term effects tillage, cover crops, and nitrogen fertilization on organic carbon and nitrogen concentrations in sandy loam soils in Georgia, USA. Soil & Tillage Research, 63: 167-179.

Tallman, S.M., 2014. Cover crop mixtures as partial summerfallow replacement in the semi-arid northern Great Plains. Master’s Thesis, Montana State University, Bozeman, MT.

USDA Farm Service Agency. 2016. Crop Acreage Data. https://www.fsa.usda.gov/news-room/efoia/electronic-reading-room/frequently-requested-information/crop-acreage-data/index. Accessed [2 Jan 2017].

van Kessel, C., and C. Hartley. 2000. Agricultural management of grain legumes: has it led to an increase in nitrogen fixation? Field Crops Research. 65:165-181.

Wardle, D.A., K.I. Bonner, G.M. Barker. 2002. Linkages between plant litter decomposition, litter quality and vegetation responses to herbivores. Functional Ecology. 16: 585-595.

Wardle, D. A., R. D. Bardgett. 2004. Human-Induced changes in large herbivorous mammal density: the consequences for decomposers. Frontiers in Ecology and Environment. 2(3): 145-153.

West and Sparling.1986. Modifications to the substrate-induced respiration method to permit measurement of microbial biomass in soils of differing water contents. Journal of Microbiological Methods. 5: 177-189.

Participation Summary
1 Farmer participating in research

Educational & Outreach Activities

10 Consultations
4 Webinars / talks / presentations

Participation Summary

1 Farmers
4 Ag professionals participated
Education/outreach description:

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.

Project Outcomes

Project outcomes:

Impacts

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.
  1. 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.

Accomplishments

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

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.