Made available in DSpace on 2016-04-26T19:39:33Z (GMT). No. of bitstreams: 1 2007 - Sergio Trabali Camargo Filho.pdf: 4423367 bytes, checksum: 827592ba3f6a9d37da8d784b6ae6ffe8 (MD5) Previous issue date: 2009-12-18 / The environmental conditions of light, temperature and water availability, along with grazing, are major factors establishing growth and phenology of forage species. The climatic effects imprint dynamics specific to pasture ecosystems, which are generally referred as "seasonality of the pasture." This study was set in an area of Fragiudult soil, located in Serop?dica municipality, Rio de Janeiro State, Brazil. The experiment began with a cut to make uniform the pasture at the height of 0.05 m, in February 2002. The aim was to determine the influence of climatic and genotypes factors in the expression of features of production, also the partition of carbon and nutrients in the aerial and ground parts of the perennial grasses Cynodon nlemfuensis (stargrass Puerto Rico); Cynodon spp (Tifton-85 grass); Digitaria swazilandensis (swazi grass) and Digitaria decumbens cv. Transvala (Transvala grass). Two hypotheses were formulated to guide the study: i) in the drier periods of the year, the fodder allocate more carbon and nutrients in roots than in the aerial parts of the plants; ii) the species have more or less plasticity to respond to seasonal climatic fluctuations, and periodic defoliation, evidencing differential adaptive capabilities. To check these possibilities, it was used a simple strategy trial, where, from the cut for uniformity, there were evaluated eight periods, between 03/26/02 and 01/14/03, at intervals of 42 days, sampling material of aerial and root fitomass. After processing the samples, the fresh and air dry mass were determined (kg ha-1). In the root system, the accumulation and distribution of dry weight, and the length and surface area of roots to the depth of 1.0 m were determined, by sequential extraction of monoliths (1.0 dm3) from the wall of a soil trench. In sub-samples of dried and grinded aerial parts and roots, the levels of nitrogen, phosphorus, calcium and magnesium (g kg-1) were quantified. The results showed that: regardless of forage species, the root:shoot ratio (based on dry fitomass in standing fluctuated seasonally, with higher values in the dryer months of the year, and smaller in the months of highest rainfall; the species varied in their responses, evidencing the existence of phenotypic plasticity for attributes of production (accumulation of forage and root mass) and adaptive (length and specific root area), with the Tifton-85 grass outstanding by the level of productivity and stability; the magnitude of the differences between the species was controlled by the water availability, and it was amplified in the periods of increased rainfall and reduced in driest periods. The concentration of nutrients, in aerial and root biomass, responses were varied according to the nutrient, but, in general, the more nutrient concentrated in Digitaria that Cynodon, observation which was also valid for the quality of fiber. Already, the Cynodon accumulated more nutrients that Digitaria per unit area. For the relations of concentrations and accumulation of nutrients roots: shoot had little effect on the grasses and a rule, during dried periods was higher than those of rainfall period. Finally, each grass has its own dynamic in relations soil-plant-atmosphere, showing once again the different adaptive responses of these grasses. / As condi??es ambientais de luz, temperatura, disponibilidade h?drica e de nutrientes, junto com o pastejo, s?o os principais moduladores do crescimento e fenologia das esp?cies forrageiras. Os efeitos clim?ticos imprimem din?micas espec?ficas ao ecossistema pastoril, que s?o geralmente referidas como sazonalidade das pastagens . O presente trabalho foi realizado em uma ?rea de solo Planossolo, localizada no munic?pio de Serop?dica, RJ. O prop?sito foi o de determinar a influ?ncia dos fatores clim?ticos e genot?picos na express?o de caracter?sticas produtivas; assim como na parti??o de carbono e nutrientes entre as por??es a?reas e subterr?neas das gram?neas perenes Cynodon nlemfuensis (capim-Estrela Porto Rico); Cynodon spp (capim-Tifton-85); Digitaria swazilandensis (capim-su?zi) e Digitaria decumbens cv. Transvala (capim-Transvala). Foram formuladas duas hip?teses para orientar o trabalho: i) nos per?odos mais secos do ano, os capins alocam mais carbono e nutrientes nas ra?zes do que na parte a?rea; ii) os capins possuem maior ou menor plasticidade para responder ?s oscila??es clim?ticas sazonais e ? desfolha peri?dicas, evidenciando capacidades adaptativas diferenciais. Para verificar essas possibilidades, usou-se uma estrat?gia experimental simples, onde, a partir do corte de uniformiza??o, foram avaliados oito per?odos de crescimento, entre 26/03/02 e 14/01/03, a intervalos de 42 dias, com amostragens de fitomassa de parte a?rea e radicular. Ap?s processamento das amostras, foram determinadas a massa verde e massa seca da parte a?rea (kg ha-1). No sistema radicular, foram determinados o ac?mulo e a distribui??o da massa seca, al?m do comprimento e ?rea superficial das ra?zes at? a profundidade de 1,0 m, pela extra??o seq?encial de mon?litos (1,0 dm3) a partir da parede de uma trincheira de solo. Em sub-amostras secas e mo?das de parte a?rea e ra?zes foram determinados os teores de nitrog?nio, f?sforo, c?lcio e magn?sio (g kg-1). Os resultados obtidos permitiram observar que: independentemente do capim, a rela??o raiz: parte a?rea oscilou sazonalmente, tendo maiores valores nos meses mais secos do ano e menores nos meses de maior pluviosidade; os capins variaram as suas respostas, evidenciando a exist?ncia de plasticidade fenot?pica para atributos produtivos (ac?mulos de forragem e massa radicular) e adaptativos (comprimento espec?fico e ?rea radicular), tendo o capim-Tifton-85 se sobressa?do pelo n?vel de produtividade e estabilidade; a magnitude das diferen?as entre os capins foi controlada pela disponibilidade de ?gua, sendo amplificada nos per?odos de maior pluviosidade e reduzida nos per?odos mais secos. A concentra??o de nutrientes, tanto da fitomassa a?rea como da fitomassa radicular, tiveram respostas variadas de acordo com o nutriente, mas, de um modo geral, as Digitaria concentraram mais nutrientes que os Cynodon, observa??o que tamb?m foi v?lida para a qualidade da fibra. J?, os Cynodon acumularam mais nutrientes que as Digitaria por unidade de ?rea. Para as rela??es das concentra??es e ac?mulos de nutrientes ra?zes: parte a?rea teve poucos efeitos para os capins e, em geral no per?odo seco foram superiores aos dos per?odos chuvosos. Por fim, cada capim estabeleceu sua pr?pria din?mica nas rela??es solo-planta-atmosfera, evidenciando mais uma vez as diferentes respostas adaptativas destas gram?neas forrageiras.