Study on the Effect of Zeolite and Soil Texture on Quantitative and Qualitative Characteristics of Ligustrum vulgare in Different Irrigation Levels

Drought is known as one of the most important factors limiting the growth and production of plants in urban landscape. Drought has limited production of 25% of the world's agricultural lands. Water allocated to the landscape irrigation has high value and should be used optimally with high efficiency. Soil texture is a classification instrument used both in the field and laboratory to determine soil classes based on their physical texture. Soil texture can be determined using qualitative methods such as texture by feel, and quantitative methods such as the hydrometer method. Soil texture has agricultural applications such as determining crop suitability and predicting the response of the soil to environmental and management conditions such as drought or calcium (lime) requirements. Soil texture focuses on the particles that are less than two millimeters in diameter which include sand, silt, and clay. Soil texture affects the water content and drainage ability of soils. This is because texture controls the nature of soil pores, i.e. the voids or spaces between the mineral particles in a clay soil. For example, there are many minute pores or micro pores between the tiny clay particles. Being small, they tend to retain water but to exclude air. As a result, clay soils are prone to drain poorly and to become waterlogged. By contrast, sandy soils are dry soils. On the other hand, application of new techniques to maintain soil moisture is essential. One of these techniques for increasing soil water retention is use of natural moisture absorbing materials such as zeolite. Zeolites are one of the new and effective substances to improve the soil water retention and preserve water and minerals in the soil. Zeolites contain elements such as potassium, calcium, sodium, silicon, aluminum, magnesium, iron and phosphorus that can be considered as the best dietary supplement and fertilizer and play an important role in the utilization and production of the most agricultural products.Ligustrum vulgar L., belongs to the Oleaceae family, is native to warm regions, European and Asian countries including Iran. This plant is one of the most widely used perennial plants in the landscape spaces. This study was designed to investigate the effects of drought stress and soil texture on growth and some qualitative and quantitative traits of the Ligustrum vulgare.

In order to investigate the effect of zeolite and soil texture on quantitative and qualitative traits of Ligustrum vulgare under drought stress, a factorial experiment was conducted based on completely randomized design with three replications, in the greenhouse of Agricultural Faculty, Ferdowsi University of Mashhad in 2019. The treatments consisted of four types of soil texture (100% soil, 100% sand, 80% soil + 20% zeolite, 80% sand + 20% zeolite) and three levels of irrigation (25, 50 and 100% field capacity).
Plant height, number of leaves, number of lateral branches, maximum root length, root volume, shoot and root dry weight and length of lateral branches were measured in each pot. Physiochemical traits such as relative water content, electrolyte leakage and photosynthetic pigments were also measured. Statistical analysis of data was analyzed by JMP8 software. Graphs were plotted using excel and all mean comparisons were performed by LSD test at P<0.05%.

According to the results, decreasing irrigation levels reduced vegetative traits such as fresh weight and dry weight. Relative water content also decreased, but ion leakage increased by decreasing irrigation levels. The highest stem fresh weight (18 g), root fresh weight (29 g), total fresh weight (56 g) and total dry weight (20 g) were observed in soil + zeolite, and the highest leaves fresh weight, root volume and plant height were obtained in soil and soil + zeolite treatments. The lowest root volume was observed in sand and zeolite treatments which had no significant differences.  In addition, ion leakage was lower in the treatments containing zeolite than the other treatments. The highest amount of SPAD (72) and chlorophyll b (31.5 mg / g fresh weight) were observed in sand + zeolite treatment and 25% field capacity. According to the results, it seems that soil and soil + zeolite in low irrigation conditions were more suitable environment for growth of Ligustrum vulgare and sandy bedding would reduce plant growth in normal conditions as well as under drought stress.