Final report for GS19-212
There are many Southeast farmers that manage crop land for corn production either as dryland or with the use of swine and poultry waste as fertilizer. For added sustainability, these farmers could add grazing crops and beef stocker calves to their system, while their crop land is not producing corn. Currently few producers capitalize on these combined resources, although this crop-livestock diversification could potentially increase sustainability and net returns. The incorporation of large taproot brassicas, such as turnips, may mitigate potential soil compaction due to grazing pressure, while enhancing calf daily gains compared to a traditional grass cover crop.
Therefore, the proposed study will evaluate the forage yield and nutritive value, calf growth, soil characteristics, subsequent corn grain yield, and economic effects of winter grazing stocker calves on either: 1. a monoculture rye or, 2. 60 percent and 40 percent turnip mixture. The study will be conducted at three locations across eastern North Carolina for a second year of a two-year study. At each location approximately 21.85 hectares of land, planted to rye or rye-turnip mixture will be grazed by 24 spring-born commercial steer calves each year. Cover crop yield, nutritional value, and cattle body weights will be recorded throughout the grazing season. Soil and corn grain samples will also be collected from both grazed and excluded areas within each treatment to analyze soil characteristics and subsequent grain yields. Conclusions from this study will demonstrate which winter cover crop was the most practical, sustainable, and economical to implement.
- Analyze double-crop forage yield and nutritive value, specifically: dry matter, organic matter, crude protein, neutral detergent fiber, acid detergent fiber, ethanol soluble carbohydrates, in vitro organic matter disappearance, sulfur, and nitrate.
- Determine the effect of the two double-crop forage schemes on calf growth parameters: hip height, body weight, and average daily gain.
- Characterize the effect of the two double-crop forge schemes on soil parameters: soil compaction, soil fertility properties, potassium, calcium, magnesium, sulfur, organic carbon and nitrogen, particulate organic matter, and soil microbial biomass in grazed fields and no-grazing exclusions.
- Measure the impact of grazing stocker calves from two double-crop forage schemes on subsequent corn grain yield.
- Quantify the economic inputs and returns of grazing stocker cattle on double-crop forage schemes: input costs, $/kg of gain on stocker calves, $/ha of subsequent corn grain, and total net return.
- Develop and disseminate recommendations for farmers which integrate a multi-species crop-livestock system with stock calves grazing a double-crop annual forage planted after corn grain harvest.
Research Site and Experimental Design
For two-consecutive years, three cooperating farms in the Coastal Plains region of Eastern, North Carolina were utilized in the experiment: Loc 1 near Trenton, North Carolina, Loc 2 near Richlands, North Carolina, and Loc 3 Tidewater Research Station near Plymouth, North Carolina. Each cooperating farm planted a minimum of 22 ha of the two forage schemes included 1) rye monoculture (RYE) and 2) 60 rye:40 turnip mixture (MIX). Cover crop forages were no-till drilled Oct 2018 for yr 1 and September 2019 for yr 2 following corn grain harvest. Seeding rate in both years for RYE was 123.3 kg/ha of Abruzzi Cereal Rye and the MIX seeding rate was 89.7 kg/ha of Abruzzi Cereal Rye and 2.2 kg/ha of Purple Top Turnip. In addition to the two forage treatments, the study consisted of a grazed (GRAZE) and no-grazed (No-GRAZE) treatment as a split plot design. Temporary fencing was set up to divide fields into 6 grazing paddocks per location at Loc 1 and Loc 2 and 8 grazing paddocks at Loc 3 to represent the GRAZE treatment, and a portion (approximately 0.40 hectare) of each paddock was fenced off as a grazing exclusion to represent the No-GRAZE treatment. Corn was planted on between March-May following grazing. Corn was harvested between August and September for all locations in prior to planting forage cover crop treatments.
Forage Sampling and Lab Analysis
Forage biomass samples were obtained from each paddock prior to the start of grazing on December 2018 (yr 1) and January 2020 (yr 2), and once per month until grazing ceased. For biomass determination, 6 random 0.37 m2 areas were sampled in each paddock. Turnips were pulled up to measure both above and below ground biomass and rye was clipped at ground level. Additional plant species were also clipped at ground level or collected from the ground surface, which primarily included corn residue, volunteer corn, and weeds (which were designated as “other”). The biomass samples were separated by species including rye, turnip leaf and root components, and other; individually weighed and then forced-air oven dried at 60° C to determine forage DM per hectare and the botanical composition (rye, turnip leaf, and turnip root). Total forage biomass estimations included only rye for the RYE treatment and rye, turnip leaf, and turnip root for the MIX treatment.
Fresh forage samples for nutritive value were obtained alongside forage biomass samples prior to grazing and once every two weeks until grazing ceased. In the RYE paddocks, rye was randomly selected 8 to 10 times throughout the paddock, clipped at ground level, and compiled into gallon bags. In the MIX paddocks, rye and turnip were selected randomly 8 to 10 times throughout the paddock. Rye was clipped at ground level and turnips were pulled by the root. Each component (rye, turnip leaf, and turnip root) was separately compiled into gallon bags, according to species type. Forage samples were transported in a cooler with ice to the laboratory. Once at the lab, samples were chopped up into smaller particle sizes to ensure adequate freeze drying and stored at -30° C until freeze-dried and ground through a 1-mm screen using a Wiley mill. Freeze-dried sub-samples were analyzed for corrected dry matter (105° C), crude protein, neutral detergent fiber, acid detergent fiber, and non-fiber carbohydrate.
Cattle and Animal Care
A total of 136 spring-born steer calves were used over the 2 years of the study. Loc 1 utilized 24 steers/yr in yr 1 and yr 2, Loc 2 utilized 32 steers/yr in yr 1 and yr 2, and Loc 3 utilized 24 steers in yr 2 only as forage biomass availability was not sufficient (<1,000 kg/ha) in yr 1. All steers were weaned in late-summer or early-fall. Angus based, black and black-white face crossbred steers were purchased, as a previously preconditioned group in yr 1, and stratified by coat color (black or black/black-white face), temperament, initial hip height (118.4 ± 0.77 cm), and initial BW (275 ± 1.3 kg) and assigned to 1 of the 2 forage treatments at both Loc 1 and Loc 2. In yr 2, Angus*Hereford and Angus*Limousin crossbred steers were purchased from two local producers, vaccinated and dewormed, and comingled 48 d prior to the start of the study for Loc 1 and Loc 2. Steers were stratified by original farm, coat color (black or black/black-white face), temperament, initial hip height (121.9 ± 0.74 cm), and initial BW (296 ± 2.4 kg) and assigned to 1 of the 2 forage treatments at both Loc 1 and Loc 2 in a completely randomized block design. Location 3 utilized Angus based crossbred steers with Senepol influence previously preconditioned at the Cherry Research Farm near Goldsboro, North Carolina. Loc 3 steers were stratified by hair coat (hair or slick), temperament, initial hip height (118.9 ± 0.99 cm), and initial BW (338 ± 2.5 kg) and assigned to 1 of the 2 forage treatments in a completely randomized block design. The average daily gain (ADG) was calculated using the average initial BW and average final BW divided by the number of days that the steers grazed. A stocking rate of 0.61 ha/calf was utilized. Steers were removed from grazing treatments at a location when the forage biomass began to visually appear limiting (<1,000 kg/ha) at the time of monthly forage biomass collections.
Soil and Corn Sampling and Lab Analysis
Eight random 0-5 cm soil samples and 4 random 5-15 cm soil samples were collected and composited into one, 0-5 cm soil sample and one, 5-15 cm soil sample, for each GRAZE and No-GRAZE paddock per location. The 0-5 and 5-15 cm soil samples were collected using a 4 cm inside diameter probe to first measure bulk density using the core method. Soil samples were collected following corn grain harvest and prior to planting the cover crop forage treatments as an initial baseline of soil characteristics. Post forage and grazing treatment samples were also taken. Upon arrival to the lab, soil samples were oven-dried at 55° C for ≥ 72 h and weighed to determine bulk density from the measured dry weight of soil and volume of coring probe. Soil was then sieved to pass thru a 4.75 mm screen following lightly crushing with a ceramic pestle. Soil samples were sent to Soil Testing Services of North Carolina Department of Agriculture and Consumer Services.
Two, 50 g subsamples of the < 4.75 mm sieved soil were weighed into 60 mL glass jars and filled with water to achieve 50% water-filled pore space and placed in a 1 L canning jar that contained 10 mL of ~ 1 M sodium hydroxide (NaOH) to trap CO2, and one vial of water to maintain humidity. Sample jars were aerobically incubated at 25° C for 24 d. The NaOH traps were removed and replaced at 3 d. Carbon dioxide-C was measured on 3 and 24 d via titration. The day 3 NaOH trap titration with ~ 1 M hydro chloric acid (HCl) in the presence of barium chloride (BaCl2) to a phenolphthalein endpoint was used to determine soil test biological activity by measuring the initial flush of CO2 after rewetting the soil and allowing it to incubate for 3 d with a vial of water and NaOH trap. Net N mineralization was calculated as the difference in inorganic N prior to and post a 24 d incubation. A 10 g dried and sieved subsample of soil that was shaken with 20 ml of 2 M KCl for 30 min was used to determine inorganic N (NH4-N + NO2-N + NO3-N). The filtered extract was analyzed for inorganic N using salicylate-nitroprusside and hydrazine-reduction autoanalyzer techniques.
Corn grain yields were determined through hand harvest samples once corn reached the black layer stage. An initial baseline corn hand harvest measurement and post grazing treatment grain yields were collected. Three random sets of corn ear yield measurements and samples at physiological maturity were taken from all GRAZE and No-GRAZE of each forage treatment paddock at each location. At Loc 1 and Loc 3 corn ears were removed from a 4.22 m row of corn stalks and at Loc 2 a 4.42 m row of corn stalks based on the twin or single row planting method, respectively, and weighed in the field. Three random ears were taken as a subsample for dry matter analysis by drying in a forced air oven at 60°C for 48 h. Corn grain from the three subsample ears were shelled and dried again for another 24 h until a constant weight was obtained to determine corn grain yield. Corn grain yield on a kg DM/ha was determined by dividing the dry grain weight by the area collected and multiplying by the 10000 m2/ha.
The cost per hectare, revenue, and net return in U.S. dollars were calculated for each treatment (2 x 2 factorial of grazing and forage species). Cost associated with corn production included variable costs for corn seed ($247.00/ha), synthetic fertilizer (nitrogen, phosphorus, and potassium) plus the cost of a single application ($74.10/ha + $10.50/ha), lime plus single application ($49.40/ha + $10.50/ha), weed and insecticide chemical plus the cost of three separate applications ($222.30/ha and $74.10/ha, respectively + $31.49/ha), and interest on half of operating cost ($44.95/ha). Fixed costs for harvest machinery and equipment ($123.50/ha), general overhead ($53.50/ha), and land rent ($321.10/ha) were also included. Costs were determined through direct communication with producers at each location and the local Farm Credit current interest rate. The final total for corn production cost was $1262.44/ha and used for both years at each location because forage and grazing treatments did not alter corn production management practices. Revenue for corn was based on a 10 yr average U.S. corn price at $0.17/kg (USDA AMS, 2020) and multiplied by the kg/ha production for each field replicate to determine revenue per hectare for each field replicate.
Cover crop establishment cost included the cost of seed, fertilizer + application, variable machinery and equipment, fixed machinery and equipment, interest on half of operating cost, and general overhead. Cost differed between RYE and MIX ($99.24/ha and $73.66/ha, respectively) based on seeding rate and seed cost for RYE and MIX seed at $0.80/kg and $0.86/kg, respectively. In yr 2, reseeding costs were added to forage replications that had poor rye stands following the original drilling of cover crop seeds. Differing fertilizer rates at Loc 1 between yr 1 and yr 2 also caused differences in fertilizer cost and operating cost interest in yr 1 ($8.92/ha and $32.04/ha, respectively) and in yr 2 ($12.50/ha and $42.48/ha, respectively). A consistent fertilizer rate for Loc 2 and Loc 3 in both years resulted in similar cost of $16.06/ha for fertilizer and $45.94/ha for interest. Grazing cost included the initial cover crop establishment cost and reseeding cost for each forage treatment plus the cattle infrastructure cost valued at $107.60/ha which was the same for both years at each location and forage treatment. No cost for cattle infrastructure was assigned to the No-GRAZE treatment. Infrastructure cost included fence and water well and underground pipes prorated over 30 yr and portable handling facilities prorated over 10 yr. Revenue for cattle was based on a 10 yr average U.S. cattle price at $1.83/kg based out of Oklahoma City, Oklahoma at $1.83/kg (USDA AMS, 2020). Cattle price was multiplied by the kg/ha growth for each field replicate to determine revenue per hectare for each field replicate. No direct revenue was received for No-GRAZE cover crop treatments.
Forage biomass, forage nutritive value, grazing and finishing performance of steers, and carcass characteristics were analyzed using the MIXED procedure of SAS 9.3 (SAS Inst. Inc., Cary, NC) with grazing field as the experimental unit for forage and grazing performance and animal as the experimental unit for finishing performance and carcass characteristics. Year and locations were analyzed separately due to year-to-year weather variations and site variations causing differences in grazing duration. The statistical model included field block (replicate), treatment, date, and treatment by date for forage biomass and nutritive value with date as a repeated measure. Grazing and finishing performance and carcass characteristics had a statistical model including replicate and treatment (main effect). Forage treatments were considered a fixed effect in all analysis.
For soil, corn, and economic data the experimental design was a randomized complete block design for the forage treatments with a split-plot design for the grazing treatments. Baseline study data was initially screened for differences, but minimal differences and no consistent impact on study response variables were discovered; thus, baseline data was not included as a covariate. Data were analyzed using GLM procedure of SAS v. 9.3 with grazing field and no-grazing exclusion as the experimental unit and field blocks as the replicate. The statistical model included field block (replicate), forage treatment, grazing treatment, and forage by grazing for soil characteristics and corn yield data. Site by year was analyzed separately due to minor study design differences between locations and major weather difference between years. Dependent variables, including soil characteristics and subsequent grain yield were analyzed with forage and grazing treatment as fixed effects.
For all analysis, differences were considered significant at P-value ≤ 0.05, with tendencies declared at P-value > 0.05 but < 0.10. Once response variable was considered significant or a tendency then treatment differences were evaluated using the pdiff function in SAS 9.3 and treatment comparisons were considered significant at P-value ≤ 0.05, with tendencies declared when P-value is > 0.05 but < 0.10.
Forage Botanical Composition and Biomass
Botanical composition: The MIX was different between yr 1 and yr 2 at all locations. In yr 1 there was a greater proportion of rye than turnip within the total forage biomass (not statistically analyzed) and turnip had a 50:50 turnip leaf to root ratio. In yr 2 there was a greater proportion of turnip than rye within the total forage biomass (not statistically analyzed) and turnip had a 27:73 turnip leaf to root ratio.
Forage biomass data: In yr 1 at Loc 2, December and January which were not different, both had greater (P < 0.01) total forage biomass than February, and least (P < 0.01) for March. Location 2 also had greater (P < 0.05) total forage biomass for MIX than RYE. There were no additional forage treatment or date effects and no forage by date interactions for total forage biomass. In yr 2 at Loc 1 and 2, MIX had greater (P < 0.01) total forage biomass than RYE. At Loc 3, MIX had greater (P < 0.05) total forage biomass than RYE and January had greater (P < 0.01) total forage biomass than February. There were no additional forage treatment or date effects and no forage by date interactions for total forage biomass.
Forage Nutritive Value
In yr 1 at Loc 2, RYE had greater (P < 0.01) CP than MIX and decreased (P < 0.01) over time from December to February. In yr 2 at all locations, RYE had greater (P < 0.01) CP than MIX. Location 2 in yr 2 also had a decrease (P < 0.01) of CP over time. There were no additional forage treatment or date effects and no additional forage by date interactions for CP in both years.
In yr 1 both Loc 1 and Loc 2 had greater (P < 0.05) NDF and ADF for RYE than MIX and NDF and ADF increased (P < 0.01) over time at both locations. In yr 2 at Loc 2 and Loc 3, there was a forage treatment by date interaction (P = 0.05) for NDF, where RYE in February (52.0% at Loc 2 and 50.4% at Loc 3) and March (54.7% at Loc 2 only) although not different were greater (P < 0.01), followed by RYE in January (44.3% at Loc 2 and 48.7% at Loc 3), and least (P < 0.05) for MIX at any date (January, February, and March) which were not different (25.0% at Loc 2 and 30.0% at Loc 3, averaged across dates). This interaction indicates that RYE had the greatest NDF and ADF, which also continued to increase over time, while the MIX had less NDF and ADF and did not change over time. Also, in yr 2 at Loc 1, NDF and ADF were greater (P < 0.01) for RYE than MIX. Additionally, at Loc 2 RYE had greater (P < 0.01) ADF than MIX. Both Loc 1 and Loc 2 increased (P < 0.01) in ADF over time.
In yr 1 at both Loc 1 and Loc 2, NFC was greater (P < 0.05) for MIX than RYE and decreased (P < 0.01) over time. In yr 2 at Loc 3, there was a forage treatment by date interaction (P = 0.02) for NFC, in which MIX in January and February (49.8% and 46.5%, respectively) were not different but had greater (P < 0.01) NFC than RYE in January (36.4%) and was least (P < 0.05) for RYE in February (19.5%). This interaction indicates that MIX had the greatest NFC that remained constant over time, while RYE had less NFC and decreased over time. Additionally, in yr 2 at Loc 1 and Loc 2, MIX had greater (P < 0.01) NFC than RYE. There were no additional forage or grazing treatment effects and no forage by date interactions for NFC.
Grazing Steer Performance
There were no treatment effects (P ≥ 0.10) for grazing ADG, final BW, gain/ha, or hip height growth for any location in either year of the study.
There were few treatment effects on soil bulk density. At Loc 1 the MIX had greater (P = 0.05) soil bulk density than the RYE for the 0-5 cm soil depth following the first year of study treatments and a tendency (P = 0.09) for MIX to have greater soil bulk density than RYE following the second year of study treatments. At Loc 2, there was a tendency (P = 0.08) for greater soil bulk density for Graze than No-Graze at the 0-5 cm depth following the second year of study treatments. There were no other treatment effects on soil bulk density or any forage by grazing interaction.
There was no forage (P ≥ 0.10) or grazing (P ≥ 0.11) treatment effects and no forage by grazing interaction (P ≥ 0.10) for soil test biological activity in both years following study treatments at either depth across locations. There were few treatment effects on soil N mineralization. At Loc 1, for the 5-15 cm soil depth, there was a tendency (P = 0.08) for GRAZE to have greater soil microbial N mineralization than No-GRAZE following the first year of study treatments. At Loc 2, for the 0-5 cm soil depth, No-GRAZE was greater (P < 0.02) than GRAZE following the second year of study treatments. There were no other forage or grazing treatment effects and no forage by grazing interaction.
Phosphorus had a forage by grazing interaction (P = 0.02) at Loc 3 for the 5-15 cm soil depth following the first year of study treatments. In yr 1 at Loc 3, MIX*GRAZE (124 mg/dm3) was not different from RYE*No-GRAZE (115 mg/dm3), but greater (P < 0.05) than RYE*GRAZE and MIX*No-GRAZE which were not different from each other (107 and 105 mg/dm3 respectively) or RYE*No-GRAZE. Indicating a decrease of P when No-GRAZE for the MIX, but no difference between GRAZE and No-GRAZE of the RYE. At Loc 1 the second year following study treatments, at the 0-5 and 5-15 cm soil depth, GRAZE had greater (P < 0.05) P than No-GRAZE. There were no other forage or grazing treatment effects and no forage by grazing interaction for P.
Subsequent Corn Yield
The corn grain yield had a forage by grazing interaction (P = 0.03) at Loc 3 following the first year of study treatments. In yr 1 at Loc 3, MIX*GRAZE (5429 kg DM/ha) was not different than RYE*No-GRAZE (4783 kg DM/ha) or RYE*GRAZE (4075 kg DM/ha), but corn yield was greater (P < 0.05) than MIX*No-GRAZE (3742 kg DM/ha), which was not different from either RYE*No-GRAZE or RYE*GRAZE. This indicates that GRAZE resulted in an increase of corn yield for the MIX, but no difference between GARZE or No-GRAZE of the RYE. The second year following study treatments at Loc 1, there was a tendency (P = 0.08) for greater corn grain yield for GRAZE than No-GRAZE. Additionally, at Loc 2 there was a tendency (P = 0.07) for greater corn grain yield for MIX than RYE. There were no other forage or grazing treatment effects and no forage by grazing interaction for corn grain yield.
Overall System Economic Outcome
Overall net return for the entire integrated crop-livestock system: In yr 2 at Loc 3 there was a forage by grazing interaction (P = 0.04) for overall net loss. In which the MIX*GRAZE (-$633.64/ha) was not different than RYE*No-GRAZE (-$792.17/ha) or MIX*No-GRAZE (-$880.59/ha), but greater (P < 0.05) than RYE*GRAZE (-$938.54/ha), which was not different from either RYE*No-GRAZE or MIX*No-GRAZE. This indicates that GRAZE resulted in an increase of overall net return or reduction in overall net loss for the MIX, but no difference between GRAZE or No-GRAZE of the RYE. There was a tendency (P = 0.06) in yr 2 for Loc 1 to have less net loss and Loc 2 to have greater net return for MIX than RYE. Additionally, there was a tendency (P = 0.09) in yr 2 for Loc 1 to have less net loss and Loc 2 to have greater net return for GRAZE than No-GRAZE. There were no other forage or grazing treatment effects and no additional forage by grazing interactions for overall net return.
Forage Botanical Composition and Biomass
The seeding rates were designed to achieve similar total forage biomass for the RYE and MIX (60% rye and 40% turnip leaf and root). This was best achieved in yr 1, when the total (1496 kg DM/ha) forage biomass for Loc 1 was not different between forage treatments and the MIX consisted of 61% rye and 39% turnip for Loc 1 and Loc 2. However, in yr 2 the warmer drought conditions during the fall suppressed rye emergence but favored turnip growth and resulted in the reverse of yr 1 with 24% rye and 76% turnip in the MIX. Additionally, in yr 1 based on observation Loc 2 had better soil drainage than the other locations which allowed both the rye and turnip to excel in these conditions, resulting in the MIX having greater total forage biomass (1892 kg DM/ha) than RYE (1392 kg DM/ha). A mix of small grain grasses and brassicas might be most ideal for a yield boost (Helgadόttir et al., 2018), due to diversity of mineral nutrient exchange between plants (Brown, 2018). The extremely low forage biomass produced at Loc 3, approximately 1400 kg DM/ha less than the other two locations was primarily due to a three-week later planting date than the other two locations. Thus, not allowing sufficient growing degree days (GDD) of 571 GDD at Loc 3 as compared to 1117 GDD for the other two locations by December 15, 2018 when we began grazing in yr 1. Fewer growing degree days has been shown by Wiedenhoeft and Barton (1994) to substantially suppress forage yield potential.
In yr 2 all locations had sufficient growing degree days of approximately 1750 GDD by January 16, 2020 to allow enough forage growth for grazing. All three locations had an average of 2648 kg DM/ha greater total forage biomass for the MIX than RYE, due to the inclusion of the turnip root component. In yr 1 the turnip root component made up approximately 17% of the entire MIX treatment for all three locations, but in yr 2 approximately 53% of the forage MIX treatment consisted of turnip root for all three locations. A 50:50 turnip leaf to turnip root ratio was estimated in yr 1 and a 27:73 turnip leaf to turnip root ratio in yr 2 as calculated by the forage component percentages of total forage. Despite an identical seeding rate, the week earlier seeding date and warmer dry weather favored the accelerated maturity and turnip root growth causing these forage proportion and total forage biomass differences. Havilah (2011) reported turnip leaf to root ratios ranging from 90:10 within the first month of planting and 15:85 as the plant matures and begins to increase significantly in root yield, which supports the findings of the current study. Forage biomass generally decreased over time as steers consumed the forage especially in yr 1. This was also the case for Loc 1 and Loc 3 in yr 2 resulting in a similar date of grazing termination. Location 2 in yr 2 maintained a more constant forage biomass over time throughout the entire grazing duration. The excess forage biomass available at Loc 2 in yr 2 at the time of grazing termination could have potentially allowed at least another month of grazing, but steers had to be removed from fields to allow the crop producer time for preparing fields for corn planting by the first of April.
Forage Nutritive Value
Throughout the majority of the study, RYE had greater CP than the MIX forage treatment. Small grain forages such as cereal rye and oat range from 17% to 24% CP (Smart and Pruitt, 2006; Bowman et al. 2008). Crude protein for the RYE monoculture in the current study only fell within that range during yr 2 at Loc 2, while the other dates and locations had CP below 16% and as low as 10%. On the Piedmont and Coastal Plains border in Raleigh, NC, Edmisten et al. (1998) reported greater CP for cereal rye in the vegetative and boot stage (26.9% and 19.9%, respectively), but similarly reduced CP to the current study during the heading and milk stage of plant maturity at 10.1% and 7.5%, respectively. The current study based on observation would have remained in the vegetative and boot stage until the last month of grazing. Nitrogen fertilizer was applied at the recommended rate in both years for Loc 2 and Loc 3 but was under applied at Loc 1 in both years due to swine wastewater limitations. Reduced N fertilization could partially explain the reduced CP at Loc 1; however, this reduced CP trend was observed in almost every year, location, and sampling timepoint. A more likely cause for the reduced CP at all three Coastal Plains sites is the sandy soil texture (65% sand) and typically abundant precipitation. It has been reported that course or sandy soils are prone to nutrient leaching below the soils surface and out of reach of plant roots in combination with heavy precipitation (Brady, 1974; Huang and Hartemink, 2020).
Consistently, studies have reported less CP in the turnip root than the turnip leaf, averaging 11% and 18% respectively (Koch et al., 2002; Smart and Pruitt, 2006). In the current study, it is not surprising that the MIX had less CP than RYE in most locations, since turnip root made up half the turnip leaf to root ratio in yr 1 and more than half of the entire MIX total forage biomass in yr 2. A study by Lenz et al. (2019) reported turnip leaf to have even greater CP value of 24.9% than oats at 17.9%. Their results could have been due to the oats accelerated forage maturity and thus decrease of forage nutritive value during the Fall, but yet suppressed maturity for the turnip in the cooler Nebraska temperatures. A decrease in cool-season grass forage nutritive value due to increased maturity in the fall has been observed by others (Coblentz and Walgenbach, 2010), whereas nutritive value of brassicas remained steady throughout maturation (Weidenhoeft and Barton, 1994; Villalobos and Brummer, 2015). The milder winter temperatures in eastern, North Carolina did allow for the forage to mature and resulted in a trend for CP to decrease over time.
Neutral detergent fiber and ADF were consistently greater for the RYE treatment than the MIX forage treatment in both years and for all locations. Many other studies have reported cereal rye or oat NDF between 40% to 50% and ADF between 21% to 33% (Bowman et al., 2008; Edmisten et al., 1998; Lenz et al., 2019; Smart and Pruitt, 2006). Whole turnip has been reported to have an NDF of 22% and ADF of 17.5% (Sun et al., 2012; Lenz et al., 2019; Villalobos and Brummer, 2016). It is common for fiber to increase in small-gran grasses as they mature (Coblentz and Walgenbach, 2010). This was observed in the current study where NDF and ADF increased over time as the plant matured at most locations. Interestingly there was a significant treatment by date interaction for NDF in yr 2 Loc 2 and Loc 3 that indicated RYE had greater NDF and it increased over time, and the MIX had less NDF that did not decrease over time. This finding is similar to the theory that brassicas do not decrease in nutritive value over time like small grain grasses typically do with increased maturity (Weidenhoeft and Barton, 1994; Villalobos and Brummer, 2015). The non-fiber carbohydrate component of the MIX was greater than RYE, which is exactly opposite of the greater fiber for RYE than MIX trend discussed earlier. The NFC also decreased over time as the fibrous component of the plant increased. Plant maturity and winter weathering can accelerate the decrease of NFC (Lenz et al., 2019). However, turnip roots are efficient at retaining their NFC content throughout the winter and grazing duration (Lenz et al., 2019). Similar lab measurements, such as total ethanol soluble carbohydrate have been reported in other studies of 23.8% total ethanol soluble carbohydrate for turnip as compared to only 10.6% for ryegrass (Sun et al., 2012). Lenz et al. (2019) also reported total ethanol soluble carbohydrate at 15.3% and 45.8% for the turnip leaf and root, respectively, or 21% for the entire turnip and 17% for oats. These values are slightly less than the NFC results reported in the current study. One difference is the NFC value was calculated based on other chemical composition measurements and total ethanol soluble carbohydrates were measured in a separate lab analysis described by Hall et al. (1999).
Grazing Steer Performance
Greater NFC for the MIX was expected to result in greater gain for steers grazing the MIX than RYE, based on a literature review of rye and rye-turnip mix forages for chemical composition and grazing results. Greater NFC is typically associated with greater digestibility (Lenz et al., 2019). This potential increase in digestibility is correlated with greater energy content of turnip for the animal than solely rye, that is known to decrease in digestibility as the plant matures and fiber content increases (Lenz et al., 2019). Conclusions from some studies advise to not graze turnip as a monoculture (Cassida et al., 1994; Lenz et al., 2019). However, Cassida et al. (1994) used sheep as the study animal and were making conclusions based on chemical composition of the forage rather than actual grazing results (Lenz et al., 2019). This recommendation was based on ruminant animals needing at least 27% to 30% NDF to optimize rumen function (Westwood and Mulcock, 2012); which can sometimes be difficult to achieve with solely grazing turnips. Additionally, CP has been shown to not be limiting for either rye or turnip forage as long as turnip root did not make up the majority of the forage being grazed, as previously mentioned in the forage nutritive value discussion. Thus, the current study was designed to include the increased fiber and CP of the rye for optimal rumen function with the addition of energy from the NFC component of turnip, to enhance growth. However, in the current study there were no differences in ADG for any location in either years, averaging 1.06 kg/d. The greater turnip root component especially in yr 2 could have driven the MIX to be deficient in CP thus becoming a limiting factor in supplying nitrogen to rumen microbes for maximum microbial fermentation efficiency with steers grazing the MIX (Stern and Hoover, 1979). In contrast, the reduce NFC of RYE could have been a limiting factor in supplying energy to rumen microbes for maximum microbial fermentation efficiency with steers grazing RYE (Stern and Hoover, 1979). It takes a balance of nitrogen in the form of plant CP and energy provided rapidly by NFC to maximize the efficiency of microbial growth and fermentation (Stern and Hoover, 1979), leading to greater VFA production and microbial protein synthesis ultimately used by the ruminant animal for increased growth.
Another benefit of the MIX in the current study was the increased forage biomass available as compared to RYE, which could have potentially resulted in increased DMI and thus improved steer gains. Yet no improved gains were detected. Some studies have reported that despite there being an abundance of forage available in the cool-season grass and brassica mixes, calves decide to reduce forage intake due to other factors. Some of those factors have been described as cattle being unfamiliar with the forages (Launchbaugh and Provena, 1991; Brunsvig et al., 2017), an unhealthy rumen environment due to reduced NDF and greater NFC (Drewnoski et al., 2018), or deleterious plant compounds like S-methyl cysteine sulfoxide and glucosinolates (Catanese et al., 2012; Sun et al., 2012; Barry, 2013; Brunsvig et al., 2017). Average daily gain results of this study were greater than most other studies grazing similar cool-season grass and brassica forages, which averaged 0.58 across all studies cited for cool-season grass monocultures and mixes (Smart and Pruitt, 2006; Beck et al., 2007; Dubeux et al., 2016). Bowman et al. (2008) in Arkansas achieved the most similar gains to the current study when grazing a wheat and cereal rye mix forage of 0.98 kg/d averaged over the 4-year study. Smart and Pruitt (2006) reported that heifers grazing a monoculture rye pasture gained greater (0.74 kg/d) compared to a rye-turnip mixture (0.56 kg/d) that was described to be dominated by turnip. In contrast, Riley et al. (2019) reported that steers grazing an oat-rapeseed mix containing 73% oat and 27% rapeseed, gained more than steers grazing a monoculture oat pasture (1.05 and 0.95 kg/d, respectively). One possible explanation for the inconsistencies found in animal performance associated with these variations of cool-season grasses and brassica monocultures and mixes is the greater proportions of NFC or sugars in turnips, specifically when including the root portion, could contribute to rapid digestion and decreased ruminal pH (Westwood and Mulcock, 2012) resulting in subacute acidosis. These contributing factors along with the fact that most brassica forages are typically foreign to grazing animals at first, supports the findings of Brunsvig et al. (2017) who observed less body weight (BW) gain from d 1 – 21, than from d 22 – 48 in grazing heifers. These authors indicated that adaptation to the forage contributed greatly to animal performance when grazing brassicas. Varying percentages of cool-season grasses to brassica forages making up the pastures being grazed, could also contribute variability in the nutrients being provided and subsequent variation in animal performance. It is not clear whether it is better for ruminants to graze a more fibrous monoculture, such as oat or rye, or whether an addition of brassicas with greater digestibility will increase animal gains.
Although there was no difference in Gain/ha in the current study (89 kg/ha) it was much less than other studies have reported in cool-season grass grazing trails (507 kg/ha) in Oklahoma and Arkansas (Beck et al., 2007). Dubeux et al. (2016) in Florida did however report more similar gain/ha to the current study, averaging 91 kg/ha for grazing a combination of small grain grasses and ryegrass. Both forage treatments are viable options for producers to plant as a cover crop and graze for a potential increase in productivity as both treatments surpassed the 0.90 kg/d estimate, needed in order breakeven, as reported by Beck et al. (2013). Location 2 also had a much longer grazing duration which doubled the gain/ha. However, they had to be removed from the fields by mid-March to allow for field corn preparation. These conditions of longer grazing at Loc 2 in both years would potentially be more appealing to producers looking to add grazing cattle on crop land as an additional enterprise.
Increased risk of soil compaction is a primary concern of crop producers when considering grazing cropland as soil physical properties change more rapidly than soil nutrients or soil organic C and microbial activity (Greenwood and McKenzie, 2001). Planting cover crops is often a management strategy used by producers to alleviate the onset of soil compaction due to equipment traffic during farming (Russell and Bisinger, 2015). Cover crops have been shown to improve soil health through their intricate root system especially with diverse cover crop species by creating macropores to improve the soil structure and increase water infiltration (Franzluebbers, 2007). In the current study, there was minimal differences between forage treatments other than at Loc 1 in the first year following study treatments having greater soil bulk density for the MIX (1.20 g/cm3) than RYE (1.15 g/cm3) at the 0-5 cm soil depth. However, bulk density was not affected at other soil depths, locations, or post-treatment measurements. This finding was contrary to the idea that brassicas are the best cover crop option for reducing compaction issues (SARE, 2016).
Increased compaction due to grazing is supported by the results of Scholefield et al. (1985) who reported the static compression force exerted on the soil from standing and walking cattle are 123 and 250 kPa, respectively which is greater than the force exerted by an unloaded tractor which is 80 kPa. Russell and Bisinger (2015) reported that compaction from grazing is inevitable as grazing increased soil bulk density or penetration resistance in most studies regardless of stocking density or grazing system. In the current study, across locations years and soil depth we observed no difference in soil bulk density between cover crop planted fields that were grazed (1.29 g/cm3) or not grazed (1.28 g/cm3). Another study conducted in Georgia also reported no difference in soil bulk density due to grazing cereal rye over the winter, at a 90% grazing utilization of the forage, compared to not grazing for a 2.5 yr study (Franzluebbers and Stuedemann, 2008b). Additionally, soil moisture and frozen or thawed soil conditions in relation to timing of grazing might also influence soil physical properties (Scholefield et al., 1985; da Silva et al., 2003). The mild winters of the sites for the present study was anticipated to result in greater impact of grazing on soil compaction, and thus compaction mitigation with incorporation of brassicas. Both winters were mild in temperature never reaching below freezing temperatures, with the average low for both years of the grazing duration at 4.2⁰ C. Above average precipitation during the winter grazing, totaling 31 cm from December 2018 to March 2019, was also observed during yr 1 (The Weather Company LLC, 2020). Many studies have concluded that increased moisture at the time of grazing will most likely increase the chance of compaction occurring (Scholefield et al. 1985; Greenwood and McKenzie, 2001; Bilotta et al., 2007). However, the potential increased soil compaction due to grazing in these warm and moist conditions did not occur in the two years of grazing cover crops in the current study.
Other studies have also concluded that even though some compaction at the surface (0-10 cm) can occur with grazing cropland, it is typically below the bulk density threshold level to cause a negative impact on root growth (Greenwood and McKenzie, 2001; Bell et al. 2011; Drewnoski et al., 2018). This was the case for the current study. The highest soil bulk density recorded was 1.50 g/cm3 which is below the reported threshold of 1.8 g/cm3 (Daddow and Warrington, 1983) to be the threshold for fine sandy loam soils before occurrence of reduced crop yields occur.
Cover crops have been shown to help contribute to soil organic C sequestration and soil biological diversity, and provide biologically fixed N (Franzluebbers, 2007). Drewnoski et al. (2018) stated that both the above- and below-ground plant material contribute to soil organic matter, but it is the plant root C and plant root exudates that greatly benefit the soil microbial community. In the current 2 yr study, initial (0-3 d incubation) soil test biological activity (204 mg C/kg soil or 376 kg C/ha) and soil microbial N mineralization (52 mg N/kg soil or 96 kg N/ha) averaged across year, location, and soil depth was mostly unaffected by grazing or no-grazing of either cover crop forage scheme. Leaving approximately 1000 kg DM/ha or more forage residue and allowing for regrowth, in addition to the passage of consumed plant material being deposited on the soil as manure, may have contributed to stabilizing microbial activity despite removing some of the cover crop by grazing. Results of the current study where similar to treatment outcomes of a 7 yr, integrated crop-livestock study in Georgia, that reported no differences when averaged across grazing treatments for initial (0-3 d incubation) soil test biological activity (527 mg CO2-C/kg soil) and N mineralization (49 mg N/kg soil) for cover crop either grazed or not grazed under no-till management measured from 0-20 cm soil depth (Franzluebbers and Stuedemann, 2015). On the contrary, other studies lasting more than 7 yr have reported that manure waste from grazing livestock had a positive impact on soil microbial activity (Acosta-Martinez et al., 2010). This boost in soil microbial activity resulted in a boost of decomposable organic matter in addition to decaying plant residue, as determined in the Franzluebbers and Stuedemann (2008a) 3 yr study. In support of those concepts, Drinkwater et al. (1998) determined over 15 yr that adding cattle to a legume-small grain cash crop rotation doubled the rate of soil organic C accumulation due to manure. Potentially, our lack of observed differences might have been a result of the short duration of this study as it takes numerous years before differences in soil microbial abundance and activity are observed.
Cover crops have been consistently reported to increase nutrient cycling (Franzluebbers, 2007). There is a concern that grazing of cover crops would reduce soil cover thus removing nutrients from the system that would have been retained in the soil and contributed to the subsequent cash crop (Franzluebbers, 2007). However, excessive nutrient removal is not necessarily the case with grazing, as grazing returns a majority of the nutrients removed from the cover crop in a partially digested form back to the land as feces and manure (Follett and Wilkinson, 1995). Feces added back to the soil contains partially digested and transformed plant derived P, K, Ca, and Mg which contribute to nutrient and SOM maintenance and accumulation (Russelle et al., 2007; Martins et al., 2014; Alves et al., 2019). In the current study, P was greater for GRAZE (208 mg/dm3) than No-GRAZE (137 mg/dm3) following the second year of study treatments at Loc 1 at both soil depths. Additionally, P decreased when No-GRAZE (105 mg/dm3) for the MIX as compared to GRAZE (124 mg/dm3), but no difference between GRAZE and No-GRAZE of the RYE (107 and 115 mg/dm3 respectively). These results align with the corn grain yield tendency for GRAZE to be greater than No-GRAZE at Loc 1 in yr 2 and the forage by grazing treatment interaction at Loc 3 in yr 1. A study by Ibrikci et al. (2004) concluded that corn yield response increased from 8% to 33% compared to a control with no P fertilizer, as P fertilizer rates increased. Indicating that it is likely the corn yield could have positively responded to the increased P with grazing in the current study. The dramatic difference between GRAZE and No-GRAZE on P really could have been due to the multiple animal species manure application coming from grazing cattle as well as swine wastewater application associated with the commercial swine operation at Loc 1. In Kansas it was concluded that, cattle manure application and swine effluent application although not different from each other exceeded P fertilizer target rates and resulted in greater corn yield as compared to no fertilizer control and was similar to inorganic fertilizer application (Schlegel et al., 2015).
Subsequent Corn Yield
The positive effects on soil health from the presence of cover crops, have been reported to increase the potential yield of the cash crop (Reeves et al., 1995). Adams et al. (1970) concluded that corn grain yield was greater (approximately 5800 kg/ha) when following a winter of annual cereal rye, than on land left vacant over the winter (approximately 4800 kg/ha) in Georgia. Additionally, in Maryland, Clark et al. (1994) reported corn yield to be greater following a rye and hairy vetch (Vicia villosa) mixture (6700 kg/ha) than without cover crop (5200 kg/ha).
A meta-analysis by Peterson et al. (2020) has recently concluded that there is typically no change in cash crop yield following livestock grazing of cover crops, which is often connected with minimal alteration of soil health due to grazing. This is consistent with results of the current study in which reported forage scheme and grazing had minimal impact on soil characteristics and subsequent corn grain yield (7672 kg/ha). In Georgia, subsequent cotton and peanut yield was not different between grazed and un-grazed enclosures following a rye or ryegrass cover crop, and thus were averaged across treatments at 1250 and 4150 kg/ha, respectively (Franzluebbers, 2007). Fae et al. (2009) also reported in Ohio that grazing a cover crop of annual ryegrass or cereal rye and oat mixture had no effect on subsequent corn silage production compared to no-grazed cover crops or no cover crop treatment, averaging 10400 kg/ha. A meta-analysis by Peterson et al. (2020) reported that crop yield within an integrated crop-livestock system was not different when compared to grain yield from a specialized production system. They also determined that within loamy soil locations integrated crop-livestock systems had a 5% greater crop yield than unintegrated systems. The current study did observe a tendency the second year following study treatments at Loc 1 for the GRAZE (8873 kg/ha) treatment to have greater subsequent corn yield than the No-GRAZE (7199 kg/ha). It was concluded from a meta-analysis that when grazing is included in cropping systems design, average crop yields are similar to no graze systems across a variety of management strategies and environments (Peterson et al., 2020). The limited literature available suggests that grazing cover crops will not negate the soil benefits of adding the cover crop (Drewnoski et al., 2018; Peterson et al., 2020).
Overall System Economic Outcome
If incorporating both crop and livestock production on the same land it is important to evaluate the overall net return for the entire system. In the current study these results followed a similar forage and grazing treatment trend observed for corn grain yield in yr 2. As the same few differences and trends observed in yr 2 were variable among the three locations. However, the tendencies for GRAZE at Loc 1 and MIX at Loc 2 to be greater than No-GRAZE and RYE, respectively were even more evident when the cover crop/steer net return was combined with corn net return. Additionally, Loc 3 had the similar difference for greater overall net return with MIX*GRAZE than MIX*No-GRAZE, but no other differences among the four treatments. Conversely to the variable results of the current study, Tobin et al. (2020) reported that implementing an integrated crop-livestock system increased farm profit by $42.56/ha within the first year and $107.72/ha in the second year, due to initial fence and water infrastructure cost ($49.40/ha and $33.91/ha, respectively) being covered in year 1. They concluded that with proper grazing management integrated crop-livestock systems could benefit the soil health and producers’ income (Tobin et al., 2020). A great deal of research on integrated crop-livestock systems and their associated economic outcome as compared to traditional separate crop and livestock enterprises is necessary to feel more confident in predicting financial profitability or loss for producers considering implementing an integrated crop-livestock system.
In conclusion, planting the MIX cover crop resulted in similar or greater forage biomass with less cost than planting the RYE treatment. Thus, the MIX provided less net loss or greater net return than RYE. Forage nutritive value varied with RYE having greater CP but the MIX having less NDF and ADF but greater NFC that are commonly associated with greater digestibility and increased metabolizable energy. Despite these significant forage differences, grazing ADG and gain/ha were not different at any location or year during the winter. Lastly, grazing of both forage options resulted in gains exceeding the 0.90 kg/d recommended to justify incorporating grazing cattle in a productive enterprise as long as there is adequate forage biomass produced during the fall for winter grazing. Grazing either monoculture cereal rye or a rye-turnip mixture had an overall neutral effect on soil health and subsequent crop yield. There was minimal impact observed for soil bulk density, soil test biological activity, and soil N mineralization due to forage and grazing treatments. However, there was an observation of increased P for graze as compared to no-graze fields but only in the first year following grazing at Loc 1. This lack of differences observed in the soil characteristics resulted in no differences in the subsequent corn yield following two subsequent years of grazing the two forage schemes. Crop producers in eastern North Carolina should not be concerned of reduced corn yield due to planting either monoculture cereal rye or a rye-turnip mixture or allowing grazing of these forages over the winter as an integrated crop livestock system. Despite a couple of tendencies for MIX and GRAZE to increase overall net return, the variable results indicate that planting either monoculture cereal rye or a rye-turnip mixture or allowing grazing of these forages over the winter as an integrated crop livestock system will not provide additional economic profit or loss to a producer’s operation. Although the potential for increasing production and profit is possible with planting a cover crop and grazing on cropland it is important to make sure management practices allow you to achieve minimal production for positive net return.
Educational & Outreach Activities
All of the popular publications, abstracts, posters, and presentations were utilized to share results of the study to a variety of audiences as research data was collected and summarized over the past two years. The research field day at one of the research locations was intended from the original SARE grant proposal submission. We shared data from the first year of research collection regarding cover crop forage, steer performance, soil bulk density, and corn yield. We had numerous agriculture extension agents and undergraduate research assistants assisted with setting up, presenting, and breaking down for the event. Jordan L. Cox-O’Neill’s research defense was the last opportunity to share all of the integrated crop-livestock systems research data collected and summarized with scientific professions, extension agents, and producers that tunned in virtually.
Future outreach activities intended are to submit 3 manuscripts for publication:
- Evaluation of cereal rye with or without turnips on forage biomass, forage nutritive value, and stocker steer performance as part of a Southeastern U.S. integrated crop-livestock system
- Impact of cereal rye with or without turnips and grazing on soil characteristics and subsequent corn grain yield as part of a Southeastern U. S. integrated crop-livestock system
- Impacts of cereal rye with or without turnips and grazing on economic cost, revenue, and net return as part of a Southeastern U.S. integrated crop-livestock system
- This integrated crop-livestock systems project has contributed to the increasing data of these systems in the literature.
- Results have helped assure crop producers that including grazing on crop land should not cause concern of negatively impacting the land or subsequent cash crop production.
- There appears to be a tendency of increased economics for the integrated crop-livestock system over simply planting a cover crop alone. No major economic loss is expected.
- Timely cover crop planting and ideal weather conditions are critical for adequate forage biomass produced to allow grazing.
- The forage mixture (rye and turnip) produced the greatest total forage biomass and non-fiber carbohydrate.
- The forage rye monoculture produced greater crude protein, neutral detergent fiber, and acid detergent fiber compared to turnip-rye mixture.
- Both forage treatments produced adequate steers average daily gains, but no difference between forage treatments on steer performance.
- Forage biomass greatly influenced grazing duration and gain per hectare ultimately determining the profitability of grazing these forages.
- Crop producers in the Southeastern U.S. should not be concerned of grazing or not grazing either of these forage treatments on negative impacts on soil characteristics or subsequent corn yield with these stocking rates and grazing durations.
- Overall system net return was minimally impacted with no significant net loss or profit for any forage or grazing treatment.
- There was a tendency in the second year for 2 of the 3 locations to have less net loss or greater net return for the forage mixture over monoculture rye and grazing over no-grazing.
- We feel confident in these integrated crop-livestock systems being an option for producers to implement without incurring detrimental effects on soil and subsequent crop yield.
- We cannot say with certainty from these results that the new business endeavor will be profitable.
- Implementing this type of system requires a lot of communication between crop and livestock producers.
- As animal scientist my advisor and I gained a lot of additional knowledge about the intricacies and importance of soil and its impact on forage, animal, and environment.
- Sustainable agriculture is not one plan and design fits all as an integrated crop-livestock system is very complex and difficult to control components to best assess response variables of interest.
- Long-term and large-scale studies will be needed to have greater confidence in integrated crop-livestock system results.
- Including a no cover crop, no graze control would be useful to test the effectiveness of the cover crop on soil characteristics and subsequent crop yield.
- New innovative ways of controlling for different response variables, collaborating with diverse agriculture disciplines, and statistically analyzing the results will be necessary to best interpret the results.
- Determining a monetary value for agronomic benefits received by either cover crops or grazing will be useful to convince cash crop producers.