Assessment of Required Growing Degree Days Phenologic Stages and Growth of Borage in Different Sowing and densities

One of the main goals of modern farming is to better understand crop growth and development for optimal use of environmental resources and, consequently, more yield. The study of the growth and development of crops such as Borage (Borago officinalis L.) during the growing season allows the sensitive stages of plant life to be identified and managed in an optimal way and for them to achieve high yields. Since the weather condition of each region varies in different seasons, it is difficult to determine the time of sensitive stages of growth to unfavorable environmental conditions. One of the main advantages of determining the phenology of a plant is the optimal use of ecological factors to increase its performance, Because according to the meteorological statistics in each area and the determination of the temperature requirement for each phonological stage and the entire plant growth period, many of the issues of planting, including sowing date and plant density, can be identified at the best possible time and achieved more production. Thus, this experiment carried out in order to assessment of required growing degree days (GDD) phenologic stages and growth borage in different sowing and densities.
A field research was conducted as a split plot arrangement based on randomized complete block design (RCBD) with three replications at farm at experimental field of Khouzestan Ramin Agriculture and Natural Resources University, Iran during 2016-2017 cropping season. Five sowing date (15 October, 5 and 25 November, 15 December and 5 January) as main plat and four plant densities including of 6, 10, 14 and 18 plants per m-2 as sub plots comprised experimental treatment. Growth degree– day (GDD) accumulation of phenological stages (Emergence initiation, Two true leaves initiation, Flowering stem emergence, Flowering initiation, Full flowering, Seed fill initiation, Complete fill, Seed harvesting initiation, Total growth season), Dry flower yield, Plant height and Leaf area index of borage were measured. Analysis of variance and comparison of means was performed by SAS software and least significant difference test (LSD), 5% level probability, respectively.
The results showed that the effect of sowing date on the length of different phonologic periods was significant, but the effect of plant density and the interaction between sowing date and plant density on this trait was not significant. The highest and the lowest growth degree– day from sowing to different stages of growth were obtained on 15 October and 5 January, respectively. With delay in sowing, the average number of days and growth degree– day (GDD) accumulation decreased in most phonologic stages. The effect of sowing date and plant density had significant effect on flower yield and plant height. With 720.8 kg.ha-1 of dry flower yield, first sowing date (15 October) was the best treatment. Increasing of plant density was increased plant height, and flower yield. So that the highest dry flower yield was achieved with an average of 586.3 kg.ha-1 at a density with 14 plant per m-2. Interaction effect of sowing date and plant density on leaf area index was also significant. So that sowing dates of 15 October at 18 plant per m-2 had the highest leaf area index. Determining the relationship between borage phonologic stages and GDD will be very beneficial in applying the principles of management, especially in determining the appropriate sowing date.
For the highest dry flower yield in Ahvaz climate, the best sowing date for borago was 15 October and the best planting density was 14 plants per m-2. There was also significant correlation between flower yield and growth degree-day (GDD) accumulation showed that the regulation of sowing date is very important for completing growth and development stages.