Effect of N rate and time of application on atra paspalum

Atra paspalum (Paspalum atratum), is a seeded, perennial grass with good po tential for growing livestock in the humid tropics and subtropics. Compared with comparably fertilised grasses, crude protein concentration is low and production is confined to summer. These problems may be addressed by alter ing N rate and time of application. Atra paspalum cv. Suerte received 56, 1 12, 224 and 336 kg/ha N as a single application in March of each of 4 years and 28+28, 56+56, 112+112, and 168+168 kg/ha N in March+June as split appl ications on a sandy soil in Florida. In addition, there was a 0 N and a 336 kg/ha (56 kg/ha N every 35 days) treatment. With 0 N, atra paspalum produc ed 1680 kg/ha dry matter annually. Increasing single N applications (56, 11 2, 224 and 336 kg/ha) increased annual yield quadratically (3300, 4850, 755 0 and 8800 kg/ha, respectively) with yield departing from a linear phase at 260 kg/ha N. Increasing N in split applications also increased annual yiel d quadratically (3080, 5550, 7390 and 8330 kg/ha, respectively). Applying h alf the annual N in June resulted in more than twice the yield in August co mpared with a single March application of that annual rate. Greatest annual yield (9080 kg/ha) resulted from 6 applications of 56 kg/ha N. Single applications of N in March increased whole plant crude protein linea rly. Increase in in vitro organic matter digestibility (IVOMD) was generall y quadratic at each sample date, but improvement was not great. For example in June, when rain permitted appreciable growth, crude protein ranged from 5.7-7.4% and IVOMD from 49-53% with 0-336 kg/ha N. There was little improv ement in crude protein and IVOMD due to splitting N (7.5 and 54%, respectiv ely, in August after 168 kg/ha N in June). Florida cattlemen wishing to inc rease atra paspalum yield and improve its distribution should apply 112 kg/ ha N in mid-May (close to the start of the rainy season) with 56 kg/ha N in July and September. Cattlemen could consider alternatives to N fertiliser such as feeding supplements or sowing legumes with atra paspalum to increas e crude protein.