Características agronômicas e efi ciência do uso da chuva em cultivares de sorgo no semiárido.Ciência Rural, v.43, n.10, out, 2013. 1771Características agronômicas e efi ciência do uso da chuva em cultivares de sorgo no semiárido INTRODUÇÃOA região semiárida do nordeste brasileiro é caracterizada pela ocorrência de precipitações que se distribuem de maneira irregular, concentradas num curto período chuvoso, seguido de um longo período sem chuvas. Essa característica climática é o principal fator que afeta a produção agropecuária dessa região, sendo importante a aplicação de estratégias específi cas para obter maior rendimento na produção de forragens.A escassez de forragem, agravada no período seco, e o baixo valor nutritivo das forrageiras de ocorrência natural comprometem o crescimento e o desenvolvimento dos animais, acarretando queda de produtividade e comprometendo a produção de leite e

-The objective of this study was to evaluate the agronomic divergence of 25 sorghum hybrids (Sorghum bicolor L. Moench) in the semiarid region of Paraiba. A randomized block design with three replications was used for evaluation of plant height (PH), total natural matter production (TNMP) and total dry matter production (TDMP) and the percentage of components of DM (panicle, leaf blade, stem and dead matter) of the following hybrids: 866005, 866019, 866033, 866034, 866035, 866036, 866037, 866040, 866041, 866042, 866043, 866044, 870025, 870031, 870035, 870041, 870051, 870067, 870081, 870085, 870095, 1F305, BRS 610, Volumax, and XBS60329. Hybrid 1F305, followed by hybrid 866034, presented the highest average PH. There was a range from 7.679 to 20.948 kg/ha (average of 13,799 kg/ha) for TDMP. Hybrids 1F305, BRS 610 and Volumax presented less potential, and hybrids 866,041 and 866,042 were the most productive. Based on cluster analysis and subjective cut in 50% of dissimilarity, it was possible to establish four hierarchical groups, from which two stood out concerning productive characteristics. The group formed by hybrids Volumax, BRS 610, and XBS60329 presented lower averages for yield and lower percentage of panicle. Hybrids 866041 and 866042 show a higher total dry matter production, with values around 20,000 kg/ha.

The objective of this chapter was to discuss the importance of the fermentation processes for silage making and how it affects the final quality of the silage. The preservation of the forage crops as silage is based on a fermentation process that lows the pH and preserves the nutritive value of the fresh crop. The main principle is the production of lactic acid by the lactic acid bacteria from the metabolism of the water-soluble carbohydrates in the fresh crop. However, different fermentations may occur into the silo environment and it depends on the availability of substrate, the microbial populations, the moisture content, and the buffering capacity of the crop at the ensiling. The fermentation is quite important in the ensiling process because it affects the nutritional quality of the silage and the animal performance. If the fermentation does not occur as recommended and the undesirable fermentations will take place, which will result in a total spoiled feed that is potentially risky for animals and human's health. Well-fermented silage can be used in diets for ruminant animals without any risk for their health and without compromise the productive performance.

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