Respostas morfológicas e produtivas de Cenchrus purpureus (Schumach.) Morrone à frequência de colheita

Abstract

The different elephant grass genotypes have variations in their morphological and productive characteristics when submitted to different cutting ages and seasons. In this sense, the objective was to evaluate the effect of harvest frequency (60 and 90 days) on structural, morphogenic, growth and productive characteristics of Cenchrus purpureus (Schumach.) Morrone genotypes of different sizes. The research was carried out at the Experimental Farm of UFRPE, Garanhuns-PE, Brazil. The experimental period was between September 2019 and December 2021. The treatments consisted of four elephant grass genotypes (IRI 381, Elephant B, Taiwan A-146 2.37 and Mott), associated with two harvest frequencies (60 and 90 days) in the two seasons of the year (rainy and dry), which were irrigated in both seasons according to the irrigation need. The experimental design was randomized blocks in a split-plot, with four replications. For the morphogenic characteristics, the leaf appearance rate, leaf and stem elongation rate and phyllochron were studied. Regarding the structural aspects, plant height, stem diameter, leaf and stem length, population density of basal tillers and number of leaves per tiller were evaluated. For growth, the absolute growth rate and relative growth rate in plant height, leaf area index and light interception were determined. For productive aspects, forage production, leaves and stem, per cut and annual, and leaf/stem ratio were evaluated. Elephant B showed the highest rate of leaf elongation, differing from the other genotypes evaluated, at both harvest ages. For the stem elongation rate, it was observed that during the rainy season the tall genotypes did not differ from each other and showed a higher rate of stem elongation, compared to the short ones. For phyllochron, tall genotypes showed lower phyllochron in the rainy season. Structural characteristics such as plant height of tall genotypes were 40 to 60% higher than those of short stature. The population density of basal tillers of Taiwan A-146 2.37 was 30 to 37% higher compared to the other genotypes at both harvest frequencies. The stem diameter of the genotypes evaluated in the rainy season was higher for Elephant B and lower for Taiwan A-146 2.37. In the dry season, the stem elongation of the Taiwan A-146 2.37 genotypes occurred more slowly than in the rainy season. It was observed that, at the harvest frequency of 60 days, tall genotypes showed the highest relative growth rates (0.045 and 0.047 cm cm-1 day-1). In the dry season, it was found that, at 60 days, the absolute growth rate was higher (2.85 cm day-1). In the dry season, the genotypes under harvest frequency of 60 days showed a higher relative growth rate (0.045 cm cm -1 day-1). Mott and Elephant B had the highest light intercepts, with 93 and 90%, respectively. It was verified that the highest forage and stem production per cut was observed in the tall genotypes, at the harvest frequency of 90 days (8,869.4 and 5,950.2 kg of DM ha-1.cut-1, respectively). Therefore, for the morphogenic and structural traits, it is concluded that the harvesting frequencies of 60 and 90 days had an effect on the morphogenic traits of elephant grass genotypes, in which leaf elongation rates are higher with a 60-day harvest in evaluated genotypes. The Elefante B genotype was superior to the other genotypes in terms of leaf elongation at both cutting ages. The time of year also influences the morphogenic aspects of the evaluated genotypes, in which the appearance rate for the short genotypes was higher in the dry season. It is recommended to use a harvest frequency of 60 days in the dry season, regardless of the genotype, due to the higher density of basal tillers, larger leaves and shorter leaf appearance intervals, in order to favor productivity and nutritive value of the forage. For growth and yield traits, it was concluded that the IRI 381 genotype was more productive per cut and annually, using the harvest frequency of 90 days. The growth rates, regardless of the evaluated genotypes, are higher with 60 days of harvest. Aiming at better annual production of the forage harvested for the evaluated genotypes, it is recommended to use the 60-day harvest at both times of the year in the elephant grass genotypes in the Agreste region of the State of Pernambuco.