Methods for prediction of morphophysiological variables of Brachiaria decumbens grass

Abstract

The purpose of this study was to evaluate different methodologies used in the field in order to find the one that could most effectively relate to the morphophysiological condition of Brachiaria decumbens cv. Basilisk (syn. Urochloa decumbens cv. Basilisk Stapf R.D. Webster). Two light interception frequencies (LI, 85% and 95%) and two defoliation intensities were adopted as targets for the residual leaf area index (RLAI 1.3 and 1.8). The treatments consisted of evaluating different methods of measuring the canopy height (CH) through its ability to correlate with the morphophysiological variables of species B. decumbens cv. Basilisk. High correlations between the methods CH, compressed height (CHe), weighted height 1 (WH₁) and weighted height 8 (WH₈) were observed mainly with the variables total forage biomass (TFB) and leaf area index (LAI) in both residual and pre-grazing conditions. The path analysis showed degrees of multicollinearity, which determined the use of the “k” constants in order to correct the distortions of the diagonal elements of the correlation matrix X'X. Path analysis provided direct cause/effect indexes on TFB using LAI = 0.1435, photosynthesis (A) = −0.1061, CH = 0.1616, CHe = 0.0913, WH₁ = 0.1386 and WH₈ = 0.0575; on LAI using CH = 0.2404, CHe = 0.2164, WH₁ = 0.2307 and WH₈ = 0.2183; and on photosynthesis rate (A) using LAI = 0.2895, CH = 0.0203, CHe = −0.1170, WH₁ = 0.0352 and WH₈ = 0.0937. Similarity was observed between intercepts and slope coefficients for TFB prediction using CH, CHe, WH₁ and WH₈, providing mean values of 1069.57 and 204.06, respectively. Methods CH and WH₁ presented a significant correlation with most morphophysiological variables and can be used to quantify TFB and LAI, while CH and WH₈ can be used only for TFB.