Produção e características estruturais de capim-Tanzânia sob diferentes frequências de desfolhações em clima tropical Am

Abstract

This study determined the effect of different frequency of defoliation (FD) on the structural and production characteristics of Panicum maximum cv. Tanzania during the rainy season (RS) and dry season (DS) of 2015, in the Amazon region of Brazil. A randomized block design with six treatments and five replicates was used. The treatments corresponded to six FD (14; 21; 28; 35; 42 and 49 days). arranged in plots of 12 m2. Were evaluated the demographic pattern of tillering (DPT), tiller population density (TPD), canopy height (CH), leaf area index (LAI), , light interception (LI), total forage accumulation (TFA), and the leaf (LP), stem (SP) and dead material (DMP) proportions. The mean of the variables in each season was subjected to analysis of variance and the unfolding of the interaction between the different FD and the seasons were performed when significant by the F test. The means were analyzed by orthogonal polynomial contrasts using the PROC MIXED procedure of SAS software. Significant interaction (P<0.05) between FD and seasons was observed to the TPD, CH, LI, LAI and TFA variables. The TPD decreased (P < 0.0001) linearly from 891 to 560 tillers/m2 in the RS, and from 533 to 369 tillers/m2 in DS with FD from 14 to 49 days, respectively. Linear response was observed to the CH (P < 0.0001) characterized by the increase of its value with the decreasing of FD. The CH ranged from 58.72 to 117.42 cm with decreasing FD in the RS. In the DS the CH varied less than in the RS wit values between 37.69 and 49.03 cm, characterized for a quadratic adjustment (P = 0.0002). In the RS, the LAI and LI showed quadratic response (P < 0.05) with increasing from 3.60 to 6.05 and from 90.85% to 98.30% in FD from 14 to 49 days, respectively. The TFA which represents the sum of the cycles within each season, showed a quadratic adjustment (P = 0.0028) in RS with higher values for FD of 14 and 21 days, and a quadratic adjustment (P < 0.0001) in DS. In the rainy season it is recommended defoliation frequency around 21 days, corresponding to the 95% light interception and the canopy average height at 71 cm. In the dry season lower frequencies of defoliation are recommended such as every 49 days, due to high forage accumulation in relation to other frequencies in the dry season.