Assessment of Required Growing Degree Days for Phenological Stages of Roselle (Hibiscus sabdariffa L.) based on BBCH-Scale in Different Cropping Systems

Study the phenology of the medicinal plant is important to manage the timing of recurring plant primary and secondary material utilizations, seed collection, pest control, prevent harvested untimely and weed control. Based on the weather conditions each plant for completing its phenological stages needs certain amount of heat units. The use of special codes to describe Phenological stages of plants has a long tradition in agricultural science. This scale has a table of 100 sections from 0-99 designed for different phases of the plants’ growth. In this scale, the growth stages are divided into two principal and secondary stages. The principal growth stages are described using numbers from 0 to 9; each principal stage is divided into secondary stages through coding from 1 to 99. The objective of this study was to describe the Phenological growth stages of ‘Roselle’ based on BBCH scale.

Phenological stages of ‘Roselle’ were described and defined according to the extended BBCH scale. The experiment was carried out as strip plot layout based on a randomized complete block design with three replications at the Experimental Farm of the Faculty of Agriculture, Iranshahr Branch, Islamic Azad University, Iranshahr, Iran (Latitude 27o 12 ' N and longitude 60o 42' E; 591 m above sea level), during the growing season of 2013-2014. The experimental factors were: four rates of consumption of inputs and agricultural operations require in different cropping including Ecological system (No-tillage + Disk +Leveler +Furrower + 100% Manure), Conventional systems with low inputs (One-tillage + 0ne- Disk +Leveler +Furrower + 75% Manure + 25% NPK), Conventional systems with average inputs (One-tillage + Two-Disk +Leveler +Furrower + 50% Manure +50% NPK) and Conventional systems with high input (Two- tillage + Two-Disk +Leveler +Furrower + 100% NPK) and wheat straw application as residue mulch in four levels (6, 4, 2 t.ha-1 and control). In order to recognize the different stages of Roselle, three plants were appointed in each plot and monitored during growing season. All phenological stages of Roselle from germination to senescence were recorded based on BBCH.

The extended BBCH scale considers 10 principal growth stages, numbered from 0 to 9. Starting at Germination (stage 0) and ending at the beginning of the rest period (stage 9). Based on BBCH scale, nine phenological stages were recorded for Roselle that included: (0) Germination, (1) Leaf development, (2) Formation of side shoots, (3) Main stem elongation, (5) Inflorescence emergence, (6) Flowering, (7) Development of bolls, (8) ripening of sepals and (9) Seeds Senescence. Growing degree days to reach each stage were 153, 1051, 501, 506, 583, 730, 892, 349 & 246, respectively. Due to the high temperatures during the growing season of Roselle, the plant phenological stages were occurred more rapidly and the plant reaches its physiological maturity. Despite the interesting characteristics of this plant (Heat and drought tolerance), a detailed description of the phenological growth stages of Roselle has never been performed. A precise description of the different growth stages of this crop will provide a useful tool for agronomic and research activities. In this Study, the description of the phenological development of Roselle was proposed utilizing the expanded BBCH scale.

Roselle plant phenology is described here for the first time, according to the BBCH General scale. The use of extended BBCH scale for Roselle is important for successful implementation of farm management practices including disease and pest control. Based on our results it seems increasing wheat straw on the soil surface increased water holding capacity of the soil and reduced soil temperatures, which causes delay in the occurrence of Roselle phenological stages.
Acknowledgements
This research was supported by Ferdowsi University of Mashhad, Iran (code 31152)