Introduction

In the coastal plains of North Carolina, bermudagrass [Cynodon dactylon (L.) Pers.] is a widely grown forage in land receiving swine effluent application (also known as spray fields). In this region, most swine farms rely on lagoons for waste storage and application of stored waste on permitted land is the means of waste disposal. Hence, bermudagrass is deemed as a nutrient receiver crop. Two criteria that justify best fit of bermudagrass-based cropping systems in spray fields are 1) bermudagrass’ high forage accumulation and nutrient removal compared to other warm-season crop species grown in the region and 2) the opportunity to increase the timeframe for effluent application by overseeding cool-season annual crops into established bermudagrass and where frequent irrigation is required to prevent lagoon overflow.

Production of hay from bermudagrass grown in spray fields is a strategy to capture and remove nutrients applied from swine effluent. Bermudagrass hay is readily consumed by livestock. In terms of nutritive value, total digestible nutrient (TDN) concentration values for bermudagrass hay grown in North Carolina can range from 53 to 70%. Crude protein concentration can range from 6 to 23%. However, high effluent application rates can also result in higher nitrate concentration levels in the plant tissue and be potentially toxic to livestock.

Bermudagrass Cultivars 

Several cultivars of bermudagrass are readily available in the Southeast United States and to land managers of spray fields in the Coastal Plains of North Carolina. In addition to high forage accumulation and nutrient removal, desirable attributes for selection of bermudagrass cultivars to be grown in spray fields include rapid establishment, high nutritive value, and low tissue nitrate concentration. Considering increasing reports of bermudagrass stem maggot (Atherigona reversura) damage, selection of cultivars that are not as often or extensively damaged by stem maggot are a useful integrated pest management strategy. Dominant cultivars in spray fields are the vegetatively propagated cultivars such as Coastal, Midland 99, Ozark, Tifton 44 and Tifton 85.

Establishment Year

Bermudagrass fields can be established using seeds (also known as seeded-types) or vegetative material such as sprigs (also known as sprigged-types) or top growth. Sprigs are vegetative plant parts containing stolons, crown buds, and rhizomes/runners dug from an established field. Each sprig contains roots and can produce a new plant when it is transplanted. A good weed management plan, including use of herbicides, is critical to the success of bermudagrass establishment and control of competition from weeds. Diuron is a pre-emergent herbicide to be used on sprigged-type varieties that provides fair to good control of crabgrass, crowfootgrass, and goosegrass; also, it provides control of certain annual weeds. Consult with your local county extension agent for a weed and herbicide management plan before planting bermudagrass. 

During the year of establishment, canopy height (defined as the distance from the soil level to the average non extended and non-compressed height of the canopy) and canopy cover (defined as the percentage for the ground covered by bermudagrass) were monitored for cultivars Coastal, Midland 99, Ozark, Tifton 44, and Tifton 85 of bermudagrass grown on a commercial integrated swine operation in Bladen County. The soil series were Foreston loamy sand and Leon sand soil series. Bermudagrasses were planted on 6 April 2016. Canopy height and cover were evaluated once monthly from June to September.

By July (3 months after planting) of the year of establishment, canopy cover ranged from 40 to 98% and canopy height of all five cultivars was ≥ 14 inches (Figure 1). By August, the canopy cover of all cultivars was 100%. Canopy height ranged between 4 to 8 inches by June. By July, canopy cover ranged from 12 to 20 inches.

Figure 1. Canopy cover and canopy height of five bermudagrass cultivars during the year of establishment.

In spray fields, a typical calendar date application window for swine effluent on bermudagrass fields may range from April to October. Hence, under fertigation, bermudagrass may be ready to be defoliated for the first time approximately 3 to 4 months after planting in the year of establishment. Although differences in forage accumulation among cultivars were observed during the first harvest event in July (Figure 2), there were no differences among cultivars in the following three harvests. Total annual forage accumulation during the year of establishment (sum of four sampling events) ranged from 3.5 to 4.5 ton/acre and was not different among the five cultivars (Figure 2).

Figure 2. Forage accumulation by sampling date and total seasonal forage accumulation during the year of establishment for five bermudagrasses in the spray fields.

Productivity and Stem Maggot Damage

Averaged across three years, Tifton 85 had greater forage accumulation than Coastal, Ozark, and Tifton 44 (Figure 3). These results were similar in 2017; however, there were no differences among cultivars in 2016 and 2018. It is worth noting the high forage accumulation values during the year of establishment (Figure 3). Under the spray field conditions where data was collected, the five bermudagrass cultivars successfully established in the year of planting and were clipped as early as three months after planting with no apparent deleterious effects as observed by their productivity during the two years after the year of establishment. Forage accumulation values in this trial conducted at the spray fields were about twice as great as those reported for bermudagrass in non-spray field areas in North Carolina, and similar to those reported in the states south of North Carolina where the length of the growing season for bermudagrass is longer. 

Figure 3. Forage accumulation of five bermudagrass cultivars grown in spray fields for three years (2016, 2017, and 2018) and the three-year mean value.

Greater forage accumulation for ‘Tifton 85’ in 2017 are attributable to lower stem maggot damage (Figure 4). Consistently, ‘Tifton 85’ had lower bermudagrass stem maggot damage compared to the other cultivars during the assessments in 2016 and 2017. Similar results comparing bermudagrass cultivars affected by stem maggot have been reported in greenhouse and field studies conducted in states south of North Carolina. 

Figure 4. Bermudagrass stem maggot damage in Bladen County. Scale of measurement in 2016 is 1 to 5, where 1 = no damage and 5 = severe damage. Estimates in 2017 are the percent of damaged tillers. Bars are means ± 1 standard error of the mean.

Nutritive value and Nitrates

Concentration of crude protein in the harvested tissue ranged from 17.9 to 21.2% with moderate differences among cultivars in 2016 and 2018 (Figure 5). The total digestible nutrient (TDN) concentration was not different among cultivars and ranged from 61 to 63% across years. Both values, crude protein and TDN, would be adequate to meet the dietary needs of a lactating beef cow in the first 90 d after calving. The TDN/CP ratio values for all cultivars were <8 (data not shown), indicating there was adequate protein to match the energy in the forage and there is no need for supplemental protein in the diet (Moore et al., 1991).

Figure 5. Crude protein concentration of five bermudagrass cultivars during 2016 to 2018 grown in spray fields in North Carolina.

Averaged across cultivars and years, nitrate ion (NO3-) concentration values were 1.1, 0.5, and 0.4. % in 2016, 2017, and 2018 respectively, with corresponding N loadings of 221, 103, and 276 lb N /acre. The generally considered thresholds for all kinds of livestock if forage is the sole source of feed is ≤ 0.5% NO3-. Forages with NO3– concentration > 0.5% can be fed as a proportion of the rations, and there are several categories proposed in the literature (Poore et al., 2000). Out of the 55 bermudagrass hay lots harvested in this experiment, a total of nine lots had NO3– concentration values ≤ 0.5% with the highest value recorded at 1.5%. Forages with NO3– concentration > 0.5% can be fed as a proportion of the ration, and there are several categories proposed in the literature to achieve this feeding strategy (Poore et al., 2000; Hancock, 2013).

Summary 

Vegetatively propagated bermudagrass cultivars ‘Coastal’, ‘Midland 99’, ‘Ozark’, ‘Tifton 44’ and ‘Tifton 85’ grown during three years in spray field conditions averaged ~ 3.5 to 4.5 tons/acre/year of forage accumulation, while ranges were 17.9 to 21.2% for crude protein and 61 to 63% for total digestible nutrient (TDN) concentrations. These results highlight the high productivity and nutritive value to feed ruminant livestock of all the bermudagrass cultivars tested. Average nitrate ion (NO3-) concentration in the harvested tissue ranged from 0.4 to 1.1% across years and cultivars. Consistently for the two evaluations conducted, cultivar Tifton 85 was least damaged by stem maggot and hence this is attributed to the greater productivity observed in 2017 and the overall 3-year average forage accumulation values. 

References

Hancock, D. W. (2013). Nitrate toxicity (Circular 915). Athens: University of Georgia Extension. 

Poore, M., Green, J., Rogers, G., Spivey, K., & Dugan, K. (2000). Nitrate management in beef cattle (Ag-606). Raleigh: North Carolina Cooperative Extension Service, North Carolina State University. 

Moore, J. E., Kunkle, W. E., & Brown, W. F. (1991). Forage quality and the need for protein and energy supplements. Proceedings of the 40th Annual Florida Beef Cattle Short Course. Retrieved from: https://animal.ifas.ufl.edu/beef_extension/bcsc/1991/pdf/moore.pdf 

Spearman, L.R., Castillo, M.S. & Sosinski, S. (2021). Evaluation of five bermudagrass cultivars fertigated with swine lagoon effluent. Agron. J. DOI:10.1002/agj2.20633.