Evaluation of Physiological Growth Analysis of some Quinoa (Chenopodium quinoa Willd.) Varieties under Different Moisture Levels in Spring and Summer Planting Dates at South Khorasan Region

Deficit irrigation offers a solution for optimizing crop production under water stress conditions, albeit with an initial reduction in yield per unit area. Employing deficit irrigation aids in farm management in scenarios where land availability isn’t constrained, enabling the determination of optimal cultivation patterns while conserving water consumption. However, deficit irrigation may influence plant growth and development by inducing drought stress. Due to several capabilities, quinoa shows resistance to solar radiation, temperature, water availability, and atmospheric CO2 concentration, which makes it possible to cultivate it in different agricultural areas. Quinoa also has a great capacity for cultivation in dry and low-water soils. Although growth analysis sometimes provides valuable clues, it does not provide any physicochemical information related to the environmental reactions of plants; in other words, the main benefit of many quantities involved in growth analysis is to provide an accurate estimate of the ability and efficiency of the plant in the community at certain time intervals. In general, growth analysis evaluates the system based on the results of physiological manifestations. The purpose of this research was to evaluate the physiological growth analyses of three quinoa cultivars under different moisture levels in summer and spring planting dates in the South Khorasan region.

To evaluate the physiological traits of three quinoa cultivars under deficit irrigation conditions, four separate experiments were conducted using a factorial layout based on a randomized complete block design. These experiments included three replications and were carried out in two regions (Birjand and Sarbisheh) during two planting dates (March and July) in 2018-2019. The experimental factors consisted of five moisture levels (ranging from 25% to 125% of crop water requirement) and three quinoa cultivars (Titicaca, Giza1, and Redcarina). To compare the cultivars and assess the impact of humidity levels, several physiological indices—such as leaf area index (LAI), crop growth rate (CGR), relative growth rate (RGR), and net assimilation rate (NAR)—were studied. Regression curves were fitted to the data from all four experiments separately, and separate analyses of variance were also performed for each sampling time.

The trend of changes in the leaf area index (LAI) showed that the time needed to reach the maximum LAI was observed between 106 to 107 days after emergence in March and between 73 to 76 days after emergence in July in Birjand, respectively. In Sarbisheh, the maximum LAI was observed on day 104 after emergence in March and between 65 to 72 days after emergence in July. In March, in both studied areas, Redcarina had the highest LAI values (4.5 in Birjand and 6.7 in Sarbisheh), along with the maximum crop growth rate (CGR) of 17.93 g m-2 day-1 in Birjand and 20.63 g m-2 day-1 in Sarbisheh. Conversely, in July, Giza1 exhibited the highest LAI (6.4 in Birjand and 6 in Sarbisheh), along with the maximum CGR of 19.32 g m-2 day-1 in Birjand and 18.11 g m-2 day-1 in Sarbisheh. Additionally, the highest relative growth rate (RGR) and net assimilation rate (NAR) at the beginning of the growing season in March were observed for Redcarina, while in July, Giza1 demonstrated the highest RGR and NAR in both studied areas. Considering the effect of humidity levels, the highest levels of LAI, CGR, RGR, and NAR indices were observed at the 125% water requirement level. Specifically, the maximum LAI values in March (in Sarbisheh and Birjand) and August (in Sarbisheh and Birjand) were 8.2, 5.3, 6.5, and 7.2, respectively. The maximum CGR values were 28.78, 23.56, 22.96, and 26.18 g m-2 day-1, respectively. Furthermore, the highest RGR at the beginning of the growing season ranged from 0.189 to 0.214 g g-1 day-1, and the highest NAR at the beginning of the growing season ranged from 6.16 to 10.22 g m-2 day-1. Conversely, the lowest values of these indices were observed at the 25% water requirement level.

Overall, Redcarina, cultivated in March, and Giza1, cultivated in July, exhibited the most favorable growth analysis indices and grain yield compared to other cultivars. Additionally, deficit irrigation resulted in a decrease in all of these indices and grain yield.