Abstract
Bermudagrass is the most important warm-season pasture in the Southern USA with exceptional forage production potential and abiotic stress tolerance. However, it requires high nitrogen (N) supply to reach its full biomass and quality potential. Our objectives were to: (1) develop a nitrogen use efficiency (NUE) screening protocol for bermudagrass in controlled or semi-controlled conditions, (2) identify contrasting genotypes for NUE from natural variants and, (3) develop a knowledge base of NUE in bermudagrass. A collection consisting 290 Cynodon sp. genotypes was first pre-screened in the greenhouse. Thirty-nine genotypes with high NUE, five with low NUE were selected for further evaluations along with 5 checks in greenhouse and hoop-house under four N rates. Biomass, crude protein and N content were evaluated. N uptake efficiency (NUpE), N utilization efficiency (NUtE) and NUE were calculated based on biomass production. Genotypes showed significant influences (P < 0.0001) in all of the response variables. The genotype × N rate interaction was not significant for NUE in both environments. NUE had strong correlation with biomass production and NUpE, which got stronger as N rates increased. In N limiting conditions, bermudagrass showed a trade-off between biomass maintenance and crude protein content. Lower N applications increased biomass production over crude protein. However, when N is abundant the crop has the ability to improve crude protein. Several genotypes presented high NUE due their high NUtE and NUpE. Genotypes with contrasting NUE were selected and subjected to further field evaluation. Superior genotypes for NUE will be used in the breeding program to enhance NUE in bermudagrass.
Highlights
Warm season perennial grasses are the foundation of pasture systems in the Southeast USA (Evers 1985) where cattle production is one of the main agricultural products (U.S Census of Agriculture 2012)
146 plant introductions (PIs) were from the bermudagrass core collection maintained at Tifton, GA, 137 PIs from the National Plant Germplasm System (NPGS) maintained at Griffin, GA and seven are commercial cultivars
Interactions between genotypes and N rates were significant for biomass, crude protein and N utilization efficiency (NUtE) (Table 1)
Summary
Warm season perennial grasses are the foundation of pasture systems in the Southeast USA (Evers 1985) where cattle production is one of the main agricultural products (U.S Census of Agriculture 2012). 40 Page 2 of 14 range of soils, aggressive growth, grazing tolerance, and ability to produce high yields of good quality forage when soil nutrients are not restricted (Redfearn and Rice 2014). Since several varieties have been selected for a broad range of desirable characteristics such as forage yield, crude protein, digestibility, winter hardiness, and disease resistance (Burton and Monson 1984, 1988; Burton et al 1993; Taliaferro et al 2002). The forage varieties of bermudagrass are very responsive to nitrogen (N) fertilization (Burton and Jackson 1962). It is recommended to apply at least 220 kg ha-1 of N since the availability of this nutrient is considered the most limiting factor for bermudagrass production (Redfearn et al 2010)
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