Abstract

Growth analysis is a quantitative approach for description and interpretation of life cycle in plants, defined by genetic and environmental factors interaction. The objective of the study was to quantify total biomass accumulation for plant height (AP), total biomass (BT), leaf area index (IAF), crop growth rate (TCC), and net assimilation rate (TAN) for 4 forage sorghum cultivars: Caña dulce, Silo miel, Esmeralda, and Fortuna. The study was conducted under rain-fed conditions, and unsuitable soils for conventional agriculture, at the central high plateau area, Colegio de Postgraduados, Campus Montecillo, Texcoco, Estado de México, México. The experimental design was a randomized block split-plots design with factorial arrangement, and 4 replications. To 25, 55, 85 and 115 days after sowing (dds) AP, BT, IAF, TRC, and TAN showed significant differences among cultivars (p<0.05). Caña dulce showed the greater AP (202 cm), LAI (3.8) and BT (14.35 ton.ha^-1); in contrast to Fortuna with AP (90 cm) and BT (3.96 ton.ha^-1) a 115 dds. For the 25-45 dds period Caña dulce showed higher TCC (24.2 gm^-2d^-1) and TAN (10.2 gm^-2d^-1); on the other hand, Fortuna showed lower TCC (5 gm^-2d^-1) and TAN (5.51 gm^-2d^-1). The BT was positively correlated with AP, IAF, TCC (p<0.001), and TAN with TCC (p<0.001). The best variety for forage production under studied conditions was Caña dulce due to higher value for parameters shown for AP, NNP, BT, IAF, TCC, and TAN during the whole cropping cycle. Maximum total biomass accumulation was registered 115 dds, during anthesis stage with AP of 200 cm, TAN (0.1 gm^-2-1), IAF (3.9), TCC (0.3 gm^-2d^-1), followed by a marked reduction, hence, the optimal moment for forage harvest occurred to 155 dds for the best cultivar: Caña dulce.

Keywords: Sorghum; phenology; growth rate; net assimilation rate; leaf area index