Harvest Management and Genotype Effects on Sunn Hemp forage as Cover Crop to Improve Sustainable Beef Cattle Production in Southeastern USA

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Commodities

• Agronomic: grass (misc. perennial), sunnhemp
• Animals: bovine

Practices

• Animal Production: feed/forage, grazing management
• Crop Production: cover crops

 Year-round grazing is feasible in Alabama and Southern USA through the utilization of cool- and warm-season forages. This can be achieved by allowing for as much grazing as possible throughout the year. Producers should select a combination of forages with different growth cycles that will best support the objectives of their operation. Besides economic benefits, year-round pastures offer better environmental quality compared to seasonal pastures. The development of sustainable year-round pastures requires the incorporation of different types of annual and perennial grasses and legumes into the existing pastures.

A series of experiments were conducted at the George Washington Carver Agricultural Experiment Station in Tuskegee University to develop and demonstrate a profitable and sustainable year-round forage-based production system with sunn hemp forage, soybean (Glycine max)  or bermudagrass system in the summer-fall period, and annual ryegrass or ryegrass + legume (Australian pea, berseem clover, and hairy vetch pastures in the winter for goat production for the Southeastern U.S. during the last 2-3 years. Our results indicated that animals on sunn hemp (as a summer forage) or ryegrass + berseem clover combination (as a winter forage) grew 18-44% faster and reached the expected slaughter weight in less time when compared to bermudagrass or ryegrass pasture systems, respectively. The sunn hemp in the summer and fall and the RG+ BC for winter and spring grazing systems were the most productive with regards to biomass and average daily gain (ADG) production. This is probably due to higher nutritive values of forage diets throughout the year and different rumen microbial fermentation rates (Min, 2018; Min et al., 2019). For summer pasture, SH had greater dry matter production (4,200, 3,144, and 1,689 kg DM/ha), higher nutritive value, and better average daily gain than the pasture soybean and BG pasture in meat goats (Min, 2018). Sunn hemp contained higher crude protein (23.9, 16.3, and 7.3%) and lower fiber composition (as measured by neutral-detergent fiber; 56.1, 43.4, and 71.0 %) than forage soybean and Bermuda grass forages, respectively at the beginning, at the midpoint and at the end of the grazing season. Average daily gain (ADG) was highest (129.2 g/d) for goats grazing on SH and was lowest (19.7 g/d) for goats on bermudagrass and middle ADG for soybean pasture (81.1 g/d), probably due to high nutritive value of bermudagrass and lower internal parasites infection (Min, 2018).    We feel that using proper legume forages (ryegrass + berseem clover) for the winter grazing followed by summer forages can provide for a profitable year-round foraging system. However, a combination of forages used for grazing should be selected to optimize animal performance, enhance the soil property and reduce environmental impacts from animals while reducing dependency on petrochemical fertilizers. We are hoping that combining such as sunn hemp and multi-forages with legumes will increase protein output as well as restore N in the soil. A major benefit of the SH forage is the fact that it supplies the N, Ca, and organic matter for winter forage plots even after the grazing. When planting winter forages we may need no additional N or K throughout the winter and some nutrients may be available for the next warm season crop. This can serve as an alternative forage and complement our effort for a successful year-round grazing system.

Producers need on-farm demonstration trials to directly see this practice and compare it with other practices for sustainable beef cattle production. The economic analysis of each system will provide an insight into the understanding of which year-round grazing system, especially different genotypes of sunn hemp forage included is sustainable in Alabama and surrounding states with similar climatic conditions. Two farmer cooperators have been selected from Lee County and Greene County to participate in the project. Each mentor farmer will represent a treatment. This farmer will serve as model farmers to help other small farmers in the surrounding counties and across the region.

The purpose of this project is to compare the production and economic performance of different grazing systems by Alabama mentor beef producers.  The specific objectives are to:

1. To evaluate forage characteristics of four sunn hemp genotypes (AU Golden, Tropic Sun, Crescent Sunn, Ubon, and Blue Leaf) and stage of growth on herbage biomass production, nutritive value, and N fixation, and beef cattle performances (forage intake and average daily gain) to sunn hemp dietary inclusion;
2. To determine animal health and performance of beef cattle when sunn hemp is incorporated in the feeding system and when grazing multi-culture grasses, and grasses in combination with legumes followed by winter forages;
3. To identify and assess economic characteristics and optimum economic return of different beef cattle production (grasses/legumes) systems;

Two farmer cooperators, each having at least 30 animals, have agreed to participate in the project. 

Objective 1: two experiments will be conducted at the Caprine Research and Education Center (Exp. 1) and two on-farms.

Exp. 1 (at TU): The treatment will be the factorial arrangement of four sunn hemp genotypes (AU Golden, Tropic Sun, Crescent Sunn, Ubon, and Blue Leaf). A split-plot design with three replications will be implemented in which three harvest regimes (35, 55, and 75 days after planting (DAP)) will be considered as the main plot and the two plant components (leaf and stem) as subplots. Forage accumulation, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), in vitro dry matter digestibility (IVDMD), in vitro ruminal gas production (ANKOM gas production system), and ruminal fermentation characteristics over DAP will be tested on plant components. The experiment will be established in plots measuring 3 by 24 m during the summers of 2022 and 2023 with new planting and randomization plan each year. A disc harrow, typical of a conventional tillage practice, will be implemented to prepare the experimental fields. In order to evaluate the adaptation of sunn hemp to local environmental conditions under low-input systems, supplemental fertilizer, irrigation, or weed control measures will not be applied in either year. A commercial legume seed inoculant (Molokai Seed Company, Hawaii, USA) that contained Bradyrhizobium sp. (Vigna) will be used to inoculate forage-type sunn hemp cultivars seeds. Seeds at the rate of 22.5 kg/ha will be drilled using a no-till drill approximately at a depth of 2.5 cm and 0.20 m row spacing. 

Exp. 2 (two on-farm trials, 2022): The second treatment will be the factorial arrangement of two sunn hemp genotypes (AU Golden vs.  Tropic Sun) and two-stage of days after planting (DAP; stage of growth: 55 vs. 75 DAP) in a randomized complete block design.  Thirty-two growing steers (about 400-600 lbs. n = 8 per treatment; 2 replicates in each treatment) will be randomly assigned to each treatment during summer (Jun– October) and the whole herd productivity of each group will be measured. The variables measured will include body weight change, body condition score change, fecal egg counts, pasture growth, and forage chemical nutritive values changes. Visits will be made to each mentor producer to detail collaboration upon project approval. Depending on summer growing conditions, warm-season forages will be planted in April each year. Animals will be introduced 55 days after seeding or flowering (~75 DAP). Total grazing days will be calculated depending on forage availability. The interrelationship between stocking rate and grazing period or their mathematical relationships (e.g., gain/acre = ADG x days in grazing period x stocking rate) will be calculated. 

Objective 2 (two on-farm trials, 2023): treatments will be 100% sum hemp, 50% sunn hemp + 50% bermudagrass, or 100% bermudagrass forage diets distributed in a completely randomized design.  We plan to plant a 100% perennial bermudagrass, 100% sunn hemp, and its combinations (bermudagrass /sunn hemp in 50: 50%) with recommended seeding rate. To establish a successful stand of sunn hemp, the seed will be drilled and covered ½ to 1 inch deep, with the seeding rate of 40 to 50 pounds per acre in 6-inch rows. Animals will not be introduced until the pasture height is 6 inches tall.

Combining summer forage grazing followed by winter grazing (January-April) will also be conducted to see the minimum requirement of fertilizers for forage biomass production as well as restore N in the soil, thus reducing dependency on petroleum-based fertilizers. We plan to plant wheat and rye (WRG) grasses (late summer) with recommended seeding rate (in a mixture of 60 lbs/ac; Ball et al. 2002) on summer forage plots in bermudagrass, sunn hemp, and combinations of bermudagrass, and sunn hemp pastures, respectively. The interrelationship between forage combinations (e.g., the carry-over effect of soil N) will be conducted. Animals and all the experimental measurements will be the same as the summer forage system.

Objective 3: each producer will be trained to keep records. The records will include animal-related records, pasture records, and other input costs (e.g, veterinary items). We will provide ear tags, seeds, and veterinary items for all animals at the farms. The available forages and plant species will be sampled for lab analysis. Records will be kept on the actual amount consumed by animals along with the hay used. Prior to the introduction of animals into pastures, all the animals will be vaccinated with a modified-live virus (MLV) product in newly received beef calves to improve gain and immune response and animals will be dewormed with Cydectin (moxidectin; Fort Dodge Animal Health, Fort Dodge, IA, USA). Gastrointestinal parasitic load in beef cattle will be monitored by using fecal egg count (including coccidian) fortnightly.  The blood samples will be taken before and after the experiment is completed for pack cell volume and blood chemistry. Enterprise budgets will be prepared for each individual producer. Data will be analyzed using the general linear model (GLM) procedure of SAS (SAS, 1991). Differences among means, for all analyses, will be determined by the least-square means procedure with the protected F-test (P < 0.05).