The objective of this research was to quantify morphological responses of Tanzania grass (Panicum maximum Jacq. cv. Tanzania-1) under three grazing intensities in an irrigated, rotationally stocked setting. Treatments consisted of three grazing intensities represented by three post-graze forage masses (T1=1,000; T2=2,500, and T3=4,000 kg green dry mass/ha), in a randomized complete block design with four replications. During the grazing season (eight 36-d cycles; three days of grazing followed by 33 days rest), the following measurements were taken: mean sward height, leaf area index (LAI), light interception (LI), mean leaf angles, all measured on four occasions (1, 11, 22, and 33 days after grazing) of each rest period. Partial correlation analysis indicated the existence of correlation between height and LI, as well as between LAI and LI. As the grazing season progressed from spring-summer to autumn-winter, mean LAI declined. Mean critical LAI (95% LI) was 3.6 (T1), 4.0 (T2), and 4.5 (T3) and was always reached around the 22nd day after grazing. Over the season, hard grazing (lower residual mass) altered the sward structure causing shifts in plant architecture, as shown by reduced leaf angles (more horizontal), as plants begun to intercept more light per unit of leaf area. Critical LAI values suggest that relatively short rest periods may be advantageous for Tanzania grass pastures managed intensively under rotational stocking and irrigation.
