Effects of nitrogen fertilization and harvest date on yield, digestibility, fiber, and protein fractions of tropical grasses.

Abstract

To evaluate the response of three tropical forage species to varying rates of nitrogen (N) fertilization [0, 39, 78, 118, 157 kg of N/(ha x cutting)] and five summer harvests, forage DM mass and nutritive value were evaluated in a randomized complete block design with a split-split plot arrangement of treatments. Plots (n = 60) were established in 1996, and five harvests were conducted every 28 d from June through September in 1997 and 1998, with fertilizer applications occuring after each harvest. Fertilization with 78 kg of N/(ha x cutting) increased forage mass in these grasses by 129% (P < 0.01) compared with no N fertilization. Additional N did not result in further increases of forage mass. Bermudagrass (Cynodon dactylon) produced more forage DM [P < 0.01; 1,536 +/- 43 kg/(ha x cutting)] than stargrass [Cynodon nlemfuensis; 1,403 +/- 43 kg/(ha x cutting)] or bahiagrass [Paspalum notatum; 1,297 +/- 43 kg/(ha x cutting)]. Peak forage mass for all species occurred in late June and July. In vitro organic matter digestibility (IVOMD) of stargrass increased (P < 0.01) linearly with fertilization. A quadratic response to N fertilization (P < 0.01) was noted in IVOMD of bermudagrass, whereas bahiagrass was not affected. Bermudagrass was more (P < 0.01) digestible (57.5 +/- 0.4) than stargrass (54.6 +/- 0.4) and bahiagrass (51.9 +/- 0.4%). As fertilization level increased, NDF decreased linearly (P < 0.01) in all three forages. Total N concentration increased (P < 0.01) linearly as N fertilization increased in all forages. Total N concentration was highest (P < 0.01) in stargrass (2.4%, DM basis) compared with bermudagrass (2.2%) and bahiagrass (2.0%). Total N concentration was depressed in all forages for late June and July harvests (P < 0.01). Fertilization increased (P < 0.05) the concentration (% of DM) of all protein fractions. In July and August, nonprotein N was reduced 11.8% (P < 0.01), whereas ADIN increased in July (P < 0.01). Bahiagrass had less N in cell contents than did bermudagrass and stargrass but had a greater concentration of N associated with the cell wall. Managerial factors, including rates of N fertilization and harvest dates, can have profound effects on the nutritional value of forage. An increased understanding of these effects is imperative to improve supplementation programs for ruminants.

The chemical composition, fermentation profile, and microbial populations in tropical grass silages

“…The similar values of these components with different doses of N suggest that the N mainly favored the tillering of the plant over height growth. If the increased production of DM had been given by the vertical growth of plants, the plants would possibly have a higher proportion of fiber needed for their support (Johnson et al 2001).…”

Produção e valor nutritivo do capim-coastcross sob doses de nitrogênio e idades de rebrotação

“…A menor digestibilidade do capimcoastcross aos 42 dias de rebrotação e sob doses elevadas de N está associada ao aumento nos constituintes da parede celular, principalmente a lignina (Oliveira et al, 2000), além da comum redução RFC da forrageira com a maior idade e sob condições nutricionais mais favoráveis ao crescimento. Aumento na digestibilidade com a aplicação de doses crescentes de N em cultivares do gênero Cynodon também foi observado por Johnson et al (2001) e Alves et al (2001). Entretanto, Dias et al (1996), Ribeiro (2000) e Rocha et al (2001) não observaram variação na DIVMS com a adubação nitrogenada.…”

Best Management Practices (BMPs) for Nitrogen Fertilizer in Forage Grasses

“…The decrease in fraction C is desirable, because this fraction compiles the non-soluble protein, which is not degraded in the rumen [39][40][41].…”