Potential use of seeded peanuts as warm-season legumes in the U.S. southern Coastal Plains

View the project final report

• 2014 annual report

Commodities

• Agronomic: grass (misc. annual), peanuts

Practices

• Crop Production: warm-season legumes

Rhizoma peanut (Arachis glabrata Benth.) is one of the few warm-season perennial legumes available for producers in the southeastern USA. The high cost associated with planting and its slow establishment have reduced producer adoption of this legume. Seeded perennial (A. pintoi Krapov. & W.C. Greg.) and annual peanut (A. hypogea L.), with proper management, can be viable alternatives. In this project, four peanut entries were evaluated following planting in ‘Pensacola’ bahiagrass (Paspalum notatum Flügge) or Tifton-85 bermudagrass (Cynodon spp.) sod, in two independent trials. For the 'Pensacola' bahiagrass trial, treatments were: 1) A. glabrata cv. Florigraze; 2) A. glabrata cv. Ecoturf; 3) A. pintoi cv. Amarillo; 4) A. hypogea cv. TUFRunner 727; 5) Pensacola bahiagrass with N fertilizer (60 kg N ha^-1 after each harvest); and 6) Pensacola bahiagrass without N fertilizer. For the Tifton-85 trial, treatments were similar, except for the N fertilization. In both trials, the experimental design was a randomized complete block with four replications. Plots were harvested every 5 wk from May to October 2014, 2015, and 2016. In the Pensacola bahiagrass trial, total dry matter yield was similar among grass-legume mixtures, but greater yields were observed for fertilized bahiagrass. Peanut participation in botanical composition was < 15% with A. pintoi presenting less stand (6 plants m^-1) than other peanuts (13 plants m^-1). Grass in vitro digestibility (IVOMD) was affected by mixture, with bahiagrass IVOMD ranging from 498 to 525 g kg^-1. Arachis pintoi presented lower IVOMD (610 g kg^-1) compared with an average of 700 g kg^-1 for the other peanuts. Bahiagrass fertilized with N had greater herbage N concentration (19 g kg^-1) compared with an average of 15 g kg^-1 for bahiagrass from other treatments. TUFRunner N concentration (31 g kg^-1) was greater compared with an average of 25 g kg^-1 from other peanuts. Inclusion of forage peanut improved herbage nutritive value but did not increase yield. Nitrogen fertilization provided greater biomass yield and improved bahiagrass N concentration over that of grass-peanut mixtures. In the Tifton-85 trial, mixtures (306 kg DM ha^-1 harvest^-1) yielded more (P = 0.008) than unfertilized grass plots (200 kg DM ha^-1 harvest^-1) in 2015. Weed control was problematic and reduced yields in 2015, but in 2016 Ecoturf followed by Florigraze mixtures produced greater biomass than other treatments because of greater legume yields. In three out of four evaluations, N concentration was greater for A. hypogea (average of 30 g kg^-1) compared with A. glabrata cultivars (average of 25 g kg^-1). Grass yield was similar among treatments (P > 0.05), but grass N concentration was greater when mixed with A. glabrata compared with A. pintoi (16.8 vs. 14.8 g kg^-1, respectively). Because of the small contribution of legume to the swards, biological N₂-fixation by shoots was negligible in the first year, but it increased in the second year, particularly for A. glabrata mixtures. In hay systems with low N inputs, mixtures of Arachis glabrata and Tifton 85 bermudagrass performed better than seeded peanut or unfertilized Tifton85 bermudagrass.

Introduction

N fertilization is one of the largest expenses in forage based cow-calf production systems, in addition to being the most common limiting factor in their forage productivity. Decreasing the N fertilizer requirements of pastures would reduce the carbon footprint of cattle production, as well as increasing the economic benefit reaped by producers. According to Lal (2004), carbon emissions due to the production, transportation, storage, and distribution of N fertilizers can range from 3.3-6.6 kg CO₂ equivalent per kg of N produced. Currently, many producers are limiting N application in efforts to reduce cost, and some are seeing grassland degradation from the lack of this limiting factor. The integration of mixed legume/grass stands could greatly decrease this expense to Florida farmers, and increase overall productivity of their operations at the same input level. There are currently few warm-season legumes available to Florida farmers, with perennial peanut (Arachis glabrata Benth.) being the most successful. Slow and costly establishment has served as the greatest barrier to its widespread adoption, as it is vegetatively propagated and typically requires two years for full establishment before producing significant returns.  

Though N is the most abundant element in the atmosphere, it must be reduced to be useable by plants. N fixing legumes have a symbiotic relationship with bacteria that actively reduce atmospheric N₂ to NH₄, which is useable by plants for protein synthesis and growth. Therefore, an easily established, perennial warm-season legume that tolerates grazing and hay harvesting would greatly reduce the need for N fertilization in Florida cattle production systems. Pinto peanut (Arachis pintoi) is propagated by seed, and is perennial in its native regions in Brazil and in other regions of South America and Australia where it has been introduced, where it is heavily used in grazing systems. Seed propagation and perennial persistence are two key traits that could allow Pinto peanut to be used widely in the southern US, especially when used in mixed stands in existing bahiagrass pastures. Annual peanut (Arachis hypogea) is planted widely in Florida Panhandle and producers have skills and equipment for establishment. If proper grazing/harvesting management practices are used to allow the annual peanut to set pods to maturity, a seed bank might be created allowing the peanut to reseed in the following growing season. Legume propagation by seed (A. pintoi and A. hypogea) might be an option to alleviate planting costs and for faster establishment. It may also promote the forage seed industry in southeast USA.

            Perennial warm-season legumes combined with perennial warm-season grasses (e.g., pinto peanut/bahiagrass), is a potential system to explore for cattle production in North Florida. This system would both reduce N fertilization requirements as well as increasing total crude protein content of the forage, thereby reducing the land area needed per animal unit due to the increased quality of forage. By fixing atmospheric nitrogen, less commercial fertilizer will be required for equal levels of production, and increased production in many scenarios where no N is typically applied.

The general objective of this proposal was to evaluate the potential use of different peanuts (A. glabrata, A. hypogea, A. pintoi) associated to two warm-season grasses (Pensacola bahiagrass and Tifton-85). Specific objectives included the determination of forage yield, botanical composition, stand, nutritive value, N biological fixation by the legumes and transfer to associated grass, reseeding potential of seeded peanuts. The establishment of peanut into existing forage production systems in Florida should 1)decrease the need for N fertilization, 2)increase economic and biological efficiency, 3) increase biodiversity, and 4) increase overall economic and ecological sustainability of these systems.