Partial correlation analysis in the study of morphogenesis and herbage accumulation in Panicum maximum cv. 'Tanzania'/Analise de correlacao parcial no estudo da morfogenese e do acumulo de forragem de Panicum maximum cv. 'Tanzania'

The objective of this study was to evaluate, through partial correlation analysis, the degree of association between herbage accumulation and morphogenetic traits of 'Tanzania' grass (Panicum maximum Jacq.) defoliated with 95% of light interception and fertilized with nitrogen, under different planting densities. The experiment was carried out in a randomized complete design with 12 treatments and two replicates, in a 4 x 3 factorial arrangement consisting of four nitrogen rates (0, 80, 160, and 320kg [ha.sup.-1] [Yr.sup.-1]) and three planting densities (9, 25, and 49 plants [m.sup.-2]). Harvests were performed at 25cm above the soil, when the plots intercepted 95% of the incident light. The simple correlation coefficients between herbage accumulation and leaf and stem elongation rates and leaf appearance rate were high and positive. Correlation between herbage accumulation and leaf lifespan; however, was high and negative. The study of partial correlation coefficients revealed considerable changes in the correlation structure, whereby the association with stem elongation had a negative value statistically equal to zero, indicating no relationship between these variables. A similar result was observed for the correlations between herbage accumulation and leaf appearance and leaf lifespan. The partial correlation between accumulation and leaf elongation was different from zero and positive indicating a strong association. In Guinea grass cv. 'Tanzania' canopies defoliated at 95% light interception, leaf elongation is the morphogenetic variable with the highest strength of association with herbage accumulation. Key words: nitrogen, pasture management, Pearson correlation, plant density. Objetivou-se avaliar, por meio de correlacao parcial, o grau de associacao entre o acumulo de forragem e as caracteristicas morfogenicas do capim-tanzania (Panicum maximum Jacq.) desfolhado com 95% de interceptacao luminosa e adubado com nitrogenio em diferentes densidades de planta. O delineamento foi em blocos completos casualizados, com 12 tratamentos e duas repeticoes em esquema fatorial 4 x 3, constituido por 4 doses de nitrogenio (0, 80, 160 e 320kg [ha.sup.-1] [ano.sup.-1]) e tres densidades de plantas (9, 25 e 49 plantas [m.sup.-2]). As colheitas foram realizadas a 25cm do nivel do solo quando as parcelas interceptavam 95% da luz incidente. Os coeficientes de correlacao simples foram altos e positivos, entre o acumulo de forragem e as taxas de alongamento de folha e