The Urochloa spp. cultivars are largely used for forage production in tropical and humid subtropical zones in Brazil. However, in areas of transition to drier zones, the persistence of Urochloa cultivars may be jeopardized by severe drought. We aimed to quantify and describe variability in growth potential under irrigation as well as dehydration tolerance and avoidance in cultivars under severe drought of Urochloa C4 species (Urochloa brizantha, cvs. Marandu and BRS Paiaguás and Urochloa decumbens cv. Basilisk), which were hypothesized to be less dehydration tolerant than a Mediterranean C3 species (Dactylis glomerata L. cv. Medly). Two experiments were carried out in a controlled environment—one in pots and one in long tubes—each under irrigation and drought successively. Marandu and Basilisk cultivars produced double the aerial and root biomass of cv. BRS Paiaguás. Their root systems were also deeper conferring them higher dehydration avoidance; however, they exhibited lower dehydration tolerance under severe drought. Conversely, cv. BRS Paiaguás was less productive, more dehydration tolerant and, therefore, able to survive at lower soil moisture, similar to the drought tolerant cv. Medly. The BRS Paiaguás cultivar may show sward persistence where extreme drought is experienced, but results should be confirmed under field conditions.
ABSTRACT. The objective of this study was to evaluate the viability of pasture with high production capacity and the potential for production of silage using different sources and doses of nitrogen (N) by quantifying the productivity of dry matter (DM), some qualitative characteristics, the total cost of production (TC) and total operating cost (TOC) of silage production. The experimental design was randomized block in a factorial scheme with four replications including two sources of nitrogen (urea and ammonium nitrate) and five N doses (0, 50, 100, 150, and 200 kg ha -1 by cutting). The increase in N provided greater DM and crude protein content and reduced the fiber content in neutral detergent. The source of N did not affect the chemical composition, and therefore, it is recommended to use urea due to the ease of acquisition and higher economic return. The production of Mombasa silage can be economically viable due to high DM and crude protein content combined with low production costs. The smallest TC and TOC were obtained in the absence of nitrogen fertilization; however, the proper management of N ensures high productivity in cattle feed with higher total profit when using 100 kg ha Viabilidade técnica, econômica e qualidade nutricional da produção de silagem de capimmombaça RESUMO. Objetivou-se estudar a viabilidade de uma pastagem com alta capacidade produtiva e o potencial para produção de silagem de capim, utilizando fontes e doses de nitrogênio (N), quantificando-se a produtividade de matéria seca (PMS), algumas características bromatológicas, o custo total de produção (CT) e o custo operacional total (COT) da produção de silagem. O delineamento experimental foi em blocos casualizados, adotando um esquema fatorial com quatro repetições, sendo duas fontes de nitrogênio: ureia, e nitrato de amônio, e cinco doses de N (0, 50, 100, 150 e 200 kg ha -1 por corte). O incremento de N propiciou maior PMS e teor de proteína bruta, além de diminuir os teores de fibra em detergente neutro. As fontes de N, não influenciaram na composição química, e desta forma recomenda-se utilizar a ureia em função da facilidade de aquisição e maior retorno econômico. A produção de silagem de capim-Mombaça pode ser economicamente viável em função da elevada PMS e proteína bruta, aliado ao baixo custo de produção. O menor CT e COT foi obtido na ausência da adubação nitrogenada, entretanto, o manejo adequado de N garante boa produtividade e rendimento na alimentação do rebanho, com maior lucro total obtido na utilização de 100 kg ha
Limited knowledge about the agronomic potential of Paspalum species from the Americas hinders their use in pastures. The response mechanisms to water deficit and waterlogging were studied in five accessions of Paspalum sp. (P. regnellii cv. BRS Guará and BGP 397, P. conspersum BGP 402 and P. malacophyllum BGP 289 and BGP 293) and Urochloa brizantha cv. Marandu. Morphological and physiological traits at the end of the stress and after the recovery period were measured. All Paspalum accessions, especially BGP 289, BGP 402 and BGP 397, and also cv. Marandu, showed survival mechanisms to water deficit. BRS Guará showed adaptive features to waterlogging, although had with a low survival rate to water deficit. Under waterlogging, BGP 289 and cv. Marandu showed reduced growth, and after the recovery period, they presented low plant survival and root recovery. Although growth of BGP 293 was reduced during waterlogging, it presented high tiller survival rate. BGP 293, BGP 402 and BGP 397 showed adaptive potential strategies for waterlogging and water deficit. There is genetic variability among the evaluated accessions for water deficit and waterlogging stresses, suggesting that they may be used per se or as progenitors in crosses with other genotypes in breeding programmes.
O objetivo com este trabalho foi avaliar a composição botânica e química do pasto de Coastcross + Arachis pintoi; Coastcross + Arachis pintoi com 100kg/ha de nitrogênio (N); Coastcross + Arachis pintoi com 200 kg/ha de N; e Coastcross com 200kg/ha de N, nos períodos de inverno, primavera, verão e outono. Utilizouse delineamento experimental em blocos ao acaso com os tratamentos em esquema de parcelas subdivididas, com duas repetições (blocos). Avaliouse as percentagens de lâmina foliar verde, colmo+bainha verde, material morto e Arachis pintoi, bem como a razão folha/colmo (RF:C), além dos teores de proteína bruta, fibra em detergente neutro e digestibilidade in vitro da matéria seca. A utilização de 200kg/ha de N proporcionou a maior percentagem de lâmina foliar verde (32%) e de colmo+bainha verde (58%), porém com redução nas percentagens de material morto (10%). No outono e no verão houve maiores percentagens de lâmina foliar e redução do material morto. Na primavera houve maior percentagem da leguminosa na massa de forragem. A adubação nitrogenada exclusiva ou associada ao Arachis pintoi aumentou os teores de proteína bruta e digestibilidade in vitro da matéria seca e reduziu o teor de fibra em detergente neutro da Coastcross. A associação entre leguminosa, adubação nitrogenada e condições climáticas favoráveis, proporciona melhor composição botânica e valor nutritivo do pasto consorciado.
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