Dry matter production and chemical composition of Massai grass submitted to nitrogen rates and cutting heights

Abstract

The study was carried out in a greenhouse with a 4X4 factorial arrangement randomized block design in order to evaluate the effects of nitrogen rates (0, 50, 100 and 150 mg dm -3 ) associated with cutting heights (10, 15, 20 and 25 cm) on dry matter production and the chemical composition of Massai grass. The seeding was done in pots with 11 kg of soil. 10 plants were kept per pot, and there were two cuts every 35 days. Nitrogen fertilization was split between the two cuts, where the first N application occurred after the uniformity cut and the second after the first cut. In each cut the plants were separated and weighed for botanical component evaluation: leaf blade and stem + sheath. After this, the samples were homogenized and analysed for dry matter (DM), crude protein (CP) and neutral detergent fibre (NDF) content. In the first cut, the N fertilization caused a linear increase in DM production of 0.058 g pot -1 per each 1 mg dm -3 of N applied, as well as causing an increase of 0.549% in CP percentage, a 0.0124 pot -1 g increase in CP production and a reduction of 0.055% in NDF. In the second cut, N rates promoted a quadratic effect on DM production. A maximum DM production of 16.48 g pot -1 with 107.27 mg dm -3 of N was observed while CP production content was increased by 0.0092 g pot -1 for each 1 mg dm -3 N applied. In terms of linear responses to DM and PB, as well as the use efficiency calculated for Massai grass, recommended N doses range between 50 and 100 g dm -3 . Key words: Defoliation. Fertilization. Management. Panicum maximum cv. Massai. ResumoO estudo foi conduzido em casa de vegetação, considerando delineamento em blocos casualizados em arranjo fatorial 4X4, para avaliar os efeitos de quatro doses de N (0, 50, 100 e 150 mg dm -3 ) combinadas a quatro alturas de resíduo de corte (10, 15, 20 e 25 cm) e seu efeito sobre a produção de matéria seca e a composição bromatológica do capim Massai. A semeadura foi realizada em vasos com 11 kg de solo, permanecendo após o desbaste, 10 plantas por vaso, nas quais foram realizados dois cortes a cada 35 dias. A adubação nitrogenada foi parcelada entre os dois cortes, a primeira aplicação de N ocorreu após o corte de uniformização e a segunda após o primeiro corte. No momento do corte as plantas foram separadas e pesadas nos componentes botânicos de parte aérea: lâmina foliar e colmo+bainha. As amostras foram submetidas às análises de matéria seca (MS), proteína bruta (PB) e fibra em detergente neutro (FDN). No primeiro corte para cada 1mg dm -3 de N aplicado foi observado aumento na produção de MS da parte aérea em 0,058 g vaso -1 , 0,549% de incremento no teor PB e 0,0124 g vaso -1 de aumento na quantidade de PB, bem como redução de 0,055% no teor de FDN. No segundo corte a máxima produção de MS da parte aérea foi de 16,48 g vaso -1 com 107,27 mg dm -3 de N e a produção de PB aumentou 0,0092 g vaso -1 para cada 1mg dm -3 de N aplicado. Considerando as respostas lineares para produção de MS e PB, bem como a eficiência de uso calculado para o capim...

Ruminal degradation of Panicum grasses in three post-regrowth ages

“…The increased proportion of fiber constituents is associated with the rapid thickening and lignification of the cell wall with advancing plant age, mainly due to the increase in the proportion and thickness of stem in relation to the leaves. This trend is in accordance with the results obtained for grasses of the genus Panicum by Pereira et al (13) , Carvalho et al (14) and Garcez et al (26) , corroborating the increase in the concentrations of structural carbohydrates with advancing age of the plant for greater support at the vegetative stage. However, variations in the chemical composition of tropical grasses also depend on the type of cultivar, the presence of side tillers, and the light intensity, which does not make the leaf: stem ratio an exclusive determinant of the nutritional value of these species (15) .…”

“…Reductions in the degradation rate of nitrogen fractions from 34 days can reduce the amount of ammonia nitrogen available to rumen microorganisms, which use it for the synthesis of amino acids, cell structures, and growth (25) , which negatively impacts the DM degradability (Table 2). In tropical grasses, a reduction in the protein degradation rate is expected with advancing age, associated with factors such as climate, water availability, and temperature, with the incorporation of this fraction in the less soluble components of the forage (1,13) .…”