Investigation of changes in physiological characteristics and yield of Quinoa (Chenopodium quinoa Willd) under different cultivation date

Background and objectives
Quinoa is an annual plant belonging to the Amaranthus family with high adaptability in different environments and the only plant food that contains all the essential amino acids, micronutrients and vitamins and has the ability to adapt to different environments. Planting date affects the growth potential and yield of the plant by creating temperature and light restrictions and will reduce or increase plant growth. Proper planting date will produce higher economic yields without increasing additional costs and will allow the plant to show its full growth potential. Plant growth analysis is performed by a series of parameters, the most important of which are leaf area index (LAI), total dry matter (TDM), relative growth rate (RGR), crop growth rate (CGR) and net assimilation rate . A rapid increase in leaf area and maximum LAI at the beginning of plant life can lead to increase radiation intake, photosynthesis rate, and ultimately increased yield. Crop growth rate is one of the main factors affecting crop production and yield. Various studies on quinoa showed that leaf area index, crop growth rate, relative growth rate and net photosynthesis rate were affected by different planting dates.
Materials and methods
This study was conducted in the greenhouse complex of Jihad Keshavarzi in Khalil Abad, Khorasan Razavi province, Iran, in the form of a complete randomized block design with three replications and 12 different planting dates during the two crop years of 2018 and 2019. Cultivation treatments were performed once every 15 days from March 6th. During the experiment, the trend of changes in growth parameters including: LAI, TDM, RGR, CGR and NAR was Measured and estimated.
Results and
The results showed that the trend of changes in leaf area index in different dates had a slow trend at the beginning of leaf growth period, which continued until shortly before the emergence of flowers, but then the slope of leaf area index increased until the maximum leaf area index continued. With the aging of the leaves, yellowing and shedding of the lower leaves of the plant, due to the shading and re-transfer of material from the leaves to the seeds during the grain filling period, this process decreased and a relatively low decline was observed in the leaf area index. In total, the highest amount of total dry matter in two years was related to the planting date of March 6, but in general, the amount of total dry matter in the second year was less than the first year. Crop growth rate was higher than the planting date on the March 6th in both research years. Crop growth rate in the second year was generally lower than in the first year. This was due to the temperature difference in the two years of study. The relative growth rate during the Quinoa growth season was declining. The net assimilation rate among planting dates did not follow the same pattern, but overall this parameter showed a declining trend from the beginning of the season to the end of the growing season.
Conclusions
The results showed that the highest values of quinoa growth indices were related to the date of first plantings. This indicated the existence of suitable environmental conditions including suitable temperature and light to better achieve growth indices in the first dates For example, the highest index of leaf area was related to the planting date of March 20 and April 20 during two years of experiment, or other growth indicators had the highest values on March 6th. There was a difference between different planting dates in terms of the amount of growth characteristics studied.