Nitrogen Use Efficiency of Bermudagrass Genotypes in Different N Doses.

Bermuda grass is the most important warm-season pasture and hay grass in the southern USA. It has several advantages such as aggressive growth, grazing tolerance, and adaptation to a wide range of soil conditions, however, it requires high amounts of nitrogen (N) to reach its biomass production potential and quality. Our objective was to evaluate the N use efficiency (NUE) of pre-selected genotypes. A greenhouse experiment was conducted to evaluate 42 genotypes selected for high NUE, 5 for low NUE and the cultivars Midland, Tifton 85 and Cheyenne, in 4 N rates: 0, 100, 200, 400 mg N Kg^-1 of soil (-N, N1, N2, N3 respectively). The bermudagrass was planted in gallon pots containing 2 Kg of pasteurized soil with low N content. The experiment was laid out in a randomized complete block design with a two-level factorial arrangement of three replicates. The biomass production was evaluated through 4 cuts spaced by approx. 30 days. The N content of the dried samples was estimated by NIRS. The total biomass (DM) production and N content was used to calculate the NUpE (N uptake efficiency), NUtE (N utilization efficiency) and NUE. The statistical analysis indicated differences between genotypes and N rates for all the variables evaluated (P<0.0001) and significant genotype x N rates interaction for NUpE and NUtE (P<0.0001). The average DM increase substantially with the amount of N applied ranging from 3.9 g at -N to 19 g at N4. The NUE decreased with higher amounts of N, ranging from 29 g.g^-1 at N1 to 19.3 g.g^-1 at N3. At least 10 genotypes had higher NUE than all cultivars when N was applied. The genotypes showing high NUE will be further evaluated in the field in two locations aiming to select genotypes that can produce high amounts and good quality biomass with at least 10% less N fertilization.