Plant leaf area components differed with regard to their sensitivity to light competition. The potential shoot development model presented in this study could serve as a framework to integrate light responses in alfalfa crop models.

Responses of grasses to N fertilization are affected by cutting intensity although little is known regarding the interactions of these factors in warm‐season grasses. Pre‐cutting canopy height, herbage accumulation and changes in the nutritive value of warm‐season grasses in response to four different management strategies were assessed from October 2011 to September 2014. Treatments included two cutting intensities (70 vs. 50% depletion of canopy height set by 95% light interception), two N fertilization levels (zero vs. 300 kg N ha−1 year−1) and six perennial C4 grass species (Axonopus catharinensis; Cynodon spp. hybrid Tifton 85; Hemarthria altissima cv. Flórida; Megathyrsus maximus cv. Aruana; Paspalum notatum cv. Pensacola; and Urochloa brizantha cv. Marandu) grown in monoculture in a factorial experimental design. Canopy height varied among grass species, cutting intensity and N treatments, mainly among seasons, indicating that more than one management target (i.e. canopy height) existed throughout the plant growth cycle for each species. The largest herbage accumulation occurred in the N fertilization treatments for most species, regardless of cutting intensity. Nitrogen fertilization and 50% depletion of canopy height increased the leaf proportion and decreased the neutral detergent fibre content. Overall, N fertilization had a stronger positive impact than cutting intensity on the acid detergent fibre content, dry‐matter digestibility and crude protein content, but the magnitudes of the responses were species‐specific.

The canopy height (CH) at 95% light interception (LI) is a valuable defoliation frequency strategy used to handle variability in herbage accumulation throughout the year, mainly in C4 grasses. Such a strategy has been adopted as an open pasture management index, but defoliation frequency and intensity remain unsolved issues for shade-grown forages. A field experiment was conducted for 2 years to determine the influence of tree canopy (Eucalyptus dunnii) shading and nitrogen availability (0 and 300 kg N ha–1 year–1) on CH at 95% LI of six perennial tropical forage species. The plots were cut at 95% LI, and the height of the residual sward was kept at 50% of the corresponding CH at 95% LI. The shade level ranged from ~40% at the beginning of the experiment to ~60% at the end of summer 2013. Variations in CH at 95% LI occurred because of shading and across seasons. The range of these variations was species-dependent. Overall, species growing under trees showed higher CH, except for Paspalum notatum and Megathyrsus maximus in the first year. There was a significant increase in the length of the sheaths and leaves, as well as a decrease in tiller density and leaf : stem ratio in plants growing under trees. Nitrogen also had an impact on CH; however, its application did not compensate the shade effect on CH. Therefore, our results suggest that greater CH should be considered in case of defoliated, shade-grown plants and that such strategy might change throughout seasons.

Os carboidratos constituem entre 70 e 80 % da dieta dos ruminantes e são fundamentais para o atendimento de suas exigências em energia, síntese de proteína microbiana, componentes do leite e manutenção da saúde animal. As gramíneas forrageiras tropicais apresentam, normalmente, baixos teores de proteína bruta, os quais estão associados a elevados teores de fibra, que pode representar cerca de 60 % da matéria seca consumida. A fibra representa a fração dos carboidratos de digestão lenta ou indigestível do alimento que ocupa espaço no trato gastrintestinal e, em função de sua concentração e digestibilidade, impõe limitações ao consumo voluntário de matéria seca, minerais e energia. A suplementação energética ou protéica pode suprir as necessidades em energia e proteína dos microrganismos e do ruminante, proporcionando condições favoráveis ao ambiente ruminal, maximizando o crescimento microbiano e a utilização dos compostos fibrosos da forragem. A sincronização entre as fontes de carboidratos e as de nitrogênio (N) maximiza a eficiência microbiana e a diminuição da perda de N em forma de amônia e da energia dos carboidratos, promovendo melhoria na digestão da MS e, especialmente, da fração fibrosa da forragem. Neste artigo são analisados os efeitos da suplementação energética e/ou protéica sobre a degradação e o consumo da fibra de gramíneas forrageiras tropicais.

RESUMO O trevo-branco (Trifolium repensL

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Este trabalho teve como objetivo avaliar o comportamento da amoreira-preta sem espinhos cv. Xavante em Guarapuava (PR) entre os anos de 2005, 2006 e 2007. Foram avaliadas semanalmente vinte plantas para as variáveis porcentagem de brotação e porcentagem de florescimento. Os frutos de amora-preta foram colhidas duas a três vezes por semana e nos dois primeiros ciclos os frutos foram avaliados para massa média e teor de sólidos solúveis totais. A cv. Xavante apresentou boa adaptabilidade para a região de Guarapuava com brotação regular entre a segunda quinzena de agosto e final de setembro, floração entre início de outubro e meados de novembro e colheita de final de novembro a final de janeiro. A produtividade situou-se entre 2.790,5 e 5.952,9 kg ha-1, a massa média entre 4,3 e 5,1 g e o teor de sólidos solúveis entre 8,3 e 10,1%.