Evaluation of superabsorbent effect on the yield and water use efficiency of cucumber under water deficit conditions

Water deficit is known as the most important limiting factor in agricultural products, especially in the arid and semi-arid regions. Agriculture has been negatively influenced by low obtainable water and because of climate change, making water stress conditions for economic crucial plants. As Iran's major region is consisting of the arid and semi-arid areas with limited water resources, in case of the minimum plant water use is not maintained, the plant would experience drought stress and the products would suffer irreparable losses. One way for optimal use of the water resources and their preservation is the use of superabsorbent polymers which not only provide conditions for improved products quality but also results in increased water consumption efficiency in the arid and semi-arid areas. Superabsorbent polymers could absorb and retain water up to several times of their weight. Due to the drying up of the environment, the water retained in the superabsorbent will gradually discharge, and thus the soil would remain moist for a long time, without needing further irrigation. This property is the great importance to confront water shortage and reduce the harmful effects of drought stress in plantations. Superabsorbent polymers cause water retention in the soil and reduce the number of irrigation frequency up to 50%.

In this study, the effect of water stress and different levels of superabsorbent on cucumber crop (variety of super dominus hybrid) in a farm with sandy soil, in Seymareh region, Ilam province, Iran was evaluated. This experimental farm was conducted at 33° 09′ N and 47° 24′ E, and with an elevation of 982 m. Seymareh region has a Mediterranean summer and winter. The average annual precipitation is about 350 mm and the average temperature is about -2° C in the winter and about 45° Celsius degrees in the summer. The hydrophilic polymer: Super-AB-A-300 used in this study. This polymer is a granular type and produced by Rahab Resin Co. with product license holding of Iran Polymer and Petrochemical Institute. This hydrophilic polymer is a terpolymer of acrylamide, acrylic acid, and acrylate potassium. The experimental design was according to a split-plot method in a randomized complete block design that was done with 12 treatments and 3 replications. In this study, 3 different depths of irrigation were considered as the main treatment including I1, I2, I3 as 100, 80 and 60 percent of water requirement of plant respectively and different levels of superabsorbent were used as secondary treatment including S0, S1, S2 and S3, equal to 0 (control), 15, 30 and 45 g m-2 respectively. The size of each plot was 4 * 1.2 m2 including 6 lines. The Superabsorbent for each line in each plot was distributed in a depth of 30 cm from the soil surface. The cucumber variety of this plan was planted manually in April as spring planting and in August as summer planting. The space between planting rows was 20 cm, and between each plant in each line was 40 cm, so a total density of planting was 60 plants per each plot. Three grains were planted at each point which after germination, they were thinned out to one plant. From the 3 to 4 leaf stage (after the complete establishment of the seedling) the deficit irrigation treatment was applied. For planning and determining the irrigation interval, by adopting the no water stress treatment as the criterion, the soil moisture index and the soil matric potential were incorporated. The percentage of soil moisture content was measured through sampling to the depth of plant root in the days before irrigation and when the weighted mean of the volumetric soil moisture reached the allowable depletion for the cucumber plant, the next irrigation was performed; therefore, the irrigation interval was determined; concerning the treatment with no water stress (control) and simultaneously all the treatment plans with equal irrigation intervals and with different water depths were irrigated.

According to the results, the independent effect of irrigation and superabsorbent treatments at 1 percent level on cucumber crop yield was significant. The maximum and the minimum of cucumber fruit weight and crop yields were 72.86 and 56.90 g, and 3.7 and 1.97 kg m-2 related to the complete irrigation (I1) and severe drought stress (I3) respectively. Results showed that in the drought conditions, superabsorbent application increased cucumber fruit weight and crop yield compared to control treatment. Also, the independent effect of irrigation and superabsorbent treatments at 1 percent level on water use efficiency of cucumber crop was significant. The maximum and the minimum of water use efficiency were 8.11 and 6.15 kg m-3 related to the complete irrigation (I1) and severe drought stress (I3) respectively. In addition, a quadratic function was introduced as the optimum water-yield production function of cucumber crop (variety of super dominus hybrid) in the presence of superabsorbent, in sandy soil. Finally, the results showed that superabsorbent could prevent the significant reduction of cucumber crop yield in sandy soil and under drought stress conditions.