Production and nutritive value of Tifton 85 bermudagrass pastures overseeded with annual ryegrass and inoculated with diazotrophic bacteria

Abstract

The inoculation with Azospirillum brasilense has the potential to reduce the use of mineral fertilizers with efficient capacity to promote plant growth and yield. Most studies on the Azospirillum–plant association have been conducted on cereals and annual grasses. More studies are needed in perennial pastures, such as bermudagrass (Cynodon dactylon (L.) Pers.) that require substantial nitrogen (N) fertilization to maximize their production potential. Therefore, pastures based on Tifton 85 bermudagrass in association with annual ryegrass (Lolium multiflorum Lam.), which were inoculated with A. brasilense and fertilized with increasing amounts of N fertilizer and grazed by lactating Holstein cows were evaluated. Three grazing systems were evaluated: (i) Tifton 85, inoculated + 180 kg N/ha per year; (ii) Tifton 85 + 230 kg N/ha per year; and (iii) Tifton 85 + 280 kg N/ha per year. Forage samples were collected before and after grazing to evaluate the responses of the plants and animals. The forage yields of the systems were 21.0, 20.8 and 22.1 t DM/ha per year and the stocking rates were 3.9, 3.8 and 4.0 animal unit/ha per day, respectively. Crude protein, total digestible nutrients and neutral detergent fibre concentrations were 162, 560 and 667 g/kg, respectively. Inoculation in pastures planted with Tifton 85 bermudagrass in combination with ryegrass (plus 180 kg N/ha per year) had a positive effect, providing forage yield and nutritional value equivalent to those with fertilization with 230 kg N/ha per year.