Avaliação agronômica de cultivares de sorgo forrageiro no agreste paraibano

Abstract

The objective of the work was to evaluate the productive and morphological characteristics of cultivars of forage sorghum with and without mineral fertilization in the Agreste of Paraiba. The experiment was carried out from March to August 2019. It were used the cultivars of Sorghum bicolor BRS Ponta Negra (PN), Roxo (RX), Santa Eliza (SE) and Gigante Boliviano (GB). A randomized block design with a 4 × 2 factorial arrangement with four replications was used. It were evaluated four cultivars (PN, RX, SE and GB) and two fertilizations (with and without). The mineral fertilizer used was calculated to provide 20 kg of nitrogen (N), 50 kg of phosphorus (P) and 40 kg of potassium (K), being used urea as a sources for N; triple superphosphate for P e; potassium chloride for K. It was evaluated the fresh matter productivity (FMP) and dry matter productivity (DMP) getting the weight of forage mass at field. It was measured the plant height (PH) and then was performed the separation and weighing of the morphological parts as stem (S), leaf blade (LB) and panicle (PA). Laboratory evaluations were made to determine the dry matter (DM), crude protein (CP) and neutral detergent fiber (NDF) contents. The data obtained were subjected to analysis of variance and, when differences were observed, the interactions were sliced. Means were distinguished by Tukey's test. These analysis were performed with the aim of R statistical package considering a significance of P < 0.05. It was observed the interaction between fertilizer x cultivar for FMP variables (P = 0.0589) where the cultivars with higher production were PN and GB (42.8 and 39.1 t FM ha-1 , respectively), followed by SE (35.7 t FM ha-1 ), all receiving fertilization. The DMP showed a fertilizer x cultivar interaction (P = 0.0051), in which the most productive cultivars were GB and PN fertilized (14.1 e 11.1 t DM ha-1 , respectively). For the morphological characteristics were observed isolated effects for fertilizer and cultivar (P < 0.05). PH was higher in GB cultivar, followed by RX and SE, with PN being the lower value. The S percentage was similar, with a higher percentage in the cultivars PN, GB and RX. A higher proportion of LB was observed in the cultivars PN and GB, followed by SE and RX. There was no effect of cultivar for the PA variable (P = 0.6038). The fertilizer effects were verified in the morphological variables, where the fertilized cultivars had higher PH, percentage of S, lower percentage of LB and PA (P < 0.05). Regarding the bromatological composition, an effect of cultivar was observed for the content of DM (P < 0.0001) and NDF (P = 0.0006), where the cultivars GB, SE and RX presented the highest values, followed by PN. The CP content did not show any effect of fertilizer, cultivar or interaction between fertilizer and cultivar (P > 0.05). The fertilization performed at sowing increased the productive potential of the genotypes, where the most productive were Ponta Negra and Gigante Boliviano. However, when consider to using these cultivars for ensiling, there are limitations regarding the dry matter content which need to be corrected with additives.