Changes of Canopy Temperature and Some Physiological Traits of Hemp (Cannabis sativa) Under Deficit Water Stress and Zeolite Rates

Introduction Hemp is an old crop that used in oil extraction and textile. This plant has several medicinal characteristics. Drought stress is the most important environmental stresses in the world and a third of the arable land in the world is suffering from a shortage of water for agriculture. One of the ways to deal with drought stress, use the tolerant plants and application of water preservative materials in the soil. Zeolite, because of having high cation exchange and the potential of resiliency, is use to improve drought stress conditions. Some researchers have shown significant effects of zeolite on physiological traits and grain yield of different crops in many experiments.   Materials and methods To evaluate the effects of drought stress and zeolite on physiological characteristics and grain yield of hemp, an experiment was conducted in a randomized completely block design with three replications at the research farm of Shahrekord university in 2014. The main factor including irrigation in four levels (100, 80, 60 and 40% of water requirement) and the sub factor was zeolite at three levels (0, 5 and 10 t/ha). Density of hemp Seeds were 30 plants per square meter. The penman-monteith method by multiplying the crop coefficient (Kc) at different growth stages, was applied to calculate the plant daily evapotranspiration. Irrigation was done when the soil moisture in control treatment was reached to 50% field capacity. Also, volumetric flow meters were used to irrigation of other treatments (80, 60 and 40% of water requirement). Irrigation treatments was applied with opening the fourth of hemp leaf (1008 code in the growth stages of Cannabis sativa) and was continued until maturity and harvest. The latest of fully expanded leaf in flowering stage was used to calculate the leaf relative water content (RWC) and electrolyte leakage (EL). Analysis of data and the comparison of means was performed by SAS statistical software and the least significant difference (LSD) at 5 levels percent, respectively.   Results and discussion Results indicated that the interaction between zeolite and drought stress, except canopy temperature, were significant on all of traits. Also, the results showed that 100% water requirement and 10 ton zeolite per hectare was highest in grain yield, leaf area index and relative water content, while the treatment of 40% water requirement and 0 ton zeolite per hectare, had the highest percentage of electrolyte leakage from leaf. The researchers stated that the reduction of leaf area under drought stress related to reducing in cell elongation and also, was due to aging and dropping of leaves. Leaf weight in 100% water requirement and 5 ton zeolite per hectare was 24.31% more than the treatment of severe stress. Since the initial reaction of the plant to reduce water, close the stomata to prevent water loss, plant with closing the stomata on the leaf cells, prevented of dehydration in other organs. This maybe increasing leaf temperature. It may also reflection of infrared energy from the leaves, especially during the midday, take the canopy temperature higher than while the water requirement was supplied. Also, the direct relationship between loss of canopy temperature and yield under drought conditions were reported by researchers. Considering the significant positive correlation between grain yield and leaf weight in this experiment, it can be guessed that excellence in traits such as leaf weight, especially in the oil-protein plants such as hemp, helped the plant in absorption of higher amount of light, carbon dioxide and thus reached higher yield. Severe drought stress maybe take inefficiencies in the cell membrane leaves and followed by it, increase membrane permeability and electrolyte content. Also, it’s maybe that the zeolite, due to keep the water in the hemp roots environment, by blocking the signals of lack of moisture in the root, thus reduces the destruction of cell membranes and ultimately reduce electrolyte leakage in the plant leaf cells. According to the results, the researchers also showed that the highest rate of electrolyte leakage from leaf cell membrane occurred at the lowest level of irrigation. Severe drought stress may lead to the closure of the stomata and then disrupt to absorption of carbon dioxide and dry matter production. Other studies have shown a significant positive effect on grain yield, because the ability of zeolite to hold the amount of more water in the soil. It seems that by reducing the moisture content, the role of zeolite in maintaining and easier transfer of moisture in the rhizosphere was featured.   Conclusion Study of the evaluated traits showed that mineral moisture preservatives such as zeolite, had a significant role under lack of moisture condition. For example, application of zeolite under 40% moisture requirement were equals in leaf area index with no application of zeolite under 60% water requirement. In other words, with the use of zeolite, there was the possibility of producing grain yield and leaf area under use less water. Also, due to the significant positive correlation between leaf area index with leaf weight, application of zeolite under drought stress in hemp that increases yield and decreases destructive effects of drought stress such as electrolyte leakage and increasing in canopy temperature, therefore, it can be considered as a positive and reasonable result.