Aim
In arid and semi-arid regions such as Iran, drought stress is one of the major limiting factors affecting agricultural crop production. In these regions, application of deficit irrigation and superabsorbent materials into the soil as two agricultural management strategies, can be employed to mitigate the adverse effects of drought stress on cultivated plants and thereby improve water use productivity. In the present study, the effect of using different levels of the natural superabsorbent pumice under deficit irrigation conditions on the yield and water use productivity of maize (Zea mays L. cv. Maxima) was investigated.
Pumice is a volcanic rock that is very porous and lightweight due to the release of gases and volatile materials, and can float on the surface of water (the specific gravity of pumice is between 0.35 and 0.65 g cm-3). Due to its high porosity, pumice has a high potential to absorb and retain water (20 to 30 percent). Therefore, pumice can be added to the crop growth medium as a super moisture absorber.
Materials and methods
The present study was conducted as a two-factor factorial experiment based on a randomized complete block design with three replications on maize cv. Maxima in a greenhouse established in Mahneshan, Zanjan, Iran. The experimental factors included pumice moisture superabsorbent at three levels (0%, 10%, and 20% of soil weight) and irrigation level at three levels (100%, 80%, and 60% of crop water requirement). The treatment receiving 100% of the crop water requirement without pumice application was considered the control. The experiment was carried out in pots with a diameter of 30 cm and a height of 45 cm. The soil texture used in the experiment was sandy loam and the size of the pumice particles added to the soil were 1-2 cm. Each pot was filled with 20 kilograms of the soil and pumice mixture. Municipal tap water (EC=3.6 dS m-1) was used to irrigate pots. Three maize seeds were sown in each pot. At the four leaf stage, only one plant was retained to continue the experiment, while the other plants were removed. The amount of crop water required for all irrigation treatments was determined based on the crop water requirement of the control treatment. The volume of irrigation water for the control treatment in each irrigation interval, was achieved using the volumetric water balance method (Equation 1).
Eq. 1.
Where, I: the volume of water entering the pot through irrigation, O: drainage water collected from the bottom of the pot, and S: represents the compensation for the soil moisture deficit in the pot between two consecutive irrigation events, due to plant evapotranspiration and its physiological needs. At the end of the growth period, stem diameter, leaf area, plant height and fresh plant weight were measured, and water use productivity was determined by equation 2.
Eq. 2.
In Equation (2), WP: irrigation water productivity (kg m⁻³ ha-1), TPWM: the fresh weight of the plant shoot biomass (kg), and TUW: the total amount of water consumed during the growing season (m³).
Results
Based on the research results, the effect of different irrigation water levels on all measured traits, and the effect of pumice levels on plant height and stem diameter, and the interaction effects of pumice and irrigation water levels application on plant height, leaf area, plant fresh weight, and water use efficiency were significant. Furthermore, the correlation between yield, yield components, and water use productivity was positive and significant. Therefore, the reduction in the amount of yield components as a result of drought stress led to a decrease in yield and water use productivity. By adding pumice to the soil what caused reducing the negative effects of drought stress, the values of yield components increased, resulting in increasing yield and water use productivity.
The results showed, the application of 20% pumice superabsorbent significantly increased the average maize stem diameter (8.3%) compared to the control treatment (0% pumice). The application of 20% and 40% deficit irrigation on plants reduced the stem diameter by 3.8% and 7.7%, (respectively) compared to the control treatment (100% crop water requirement). Based on the results of the interaction of experimental treatments, at different irrigation levels, the application of 10% and 20% pumice increased plant height, leaf area, plant fresh weight, and water use productivity compared to the 0% pumice treatment, with the highest increase at each irrigation level was achieved in the 10% pumice treatment. In the 100% crop water requirement treatment, the increase in plant height, leaf area, plant fresh weight, and water use productivity in the 10% pumice treatment compared to 0% pumice was 18.1%, 50.4%, 38.7%, and 38.8%, respectively. In the 80% crop water requirement treatment, it was 22.2%, 27.1%, 56%, and 56.2%, respectively. In the 60% crop water requirement treatment, it was 15.9%, 36.9%, 28.6%, and 28.4%, respectively.
In each irrigation level, the application of 10% and 20% pumice, increased plant height, leaf area, fresh plant weight, and water use productivity compared 0% pumice, and the increase in 10% pumice treatment was more than 20% pumice. In this research, the highest mean values of plant height, leaf area, fresh plant weight, and water use productivity (225 cm, 5939.8 cm², 513.3 g plant⁻¹, and 8.12 kg m⁻³ ha⁻¹, respectively) were observed in the 100% crop water requirement-10% pumice treatment. The results of the present study showed that in the 80% crop water requirement treatment, adding 10% pumice to the soil increased plant height, leaf area, plant fresh weight, and water use productivity by 15.5%, 20.2%, 5.4%, and 29.2%, (respectively) compared to the control (100% crop water requirement-0% pumice).
Conclusion
The findings of the present study showed that the average plant height, leaf area, plant fresh weight, and water use productivity of maize decreased in the 80% and 60% water requirement treatments compared to the 100% water requirement treatment. By adding 10% and 20% pumice superabsorbent to the growth medium, the measured traits increased at all irrigation levels compared to the 0% pumice treatment, and the increase in the 10% pumice treatment was greater than that of 20% pumice. The reason for this condition could be due to the accumulation of salt in the soil medium in this treatment. According to the results of this study, the average measured traits in the 80% crop water requirement-10% pumice treatment were higher than the control treatment (100% crop water requirement-0% pumice), so it is recommended to apply this treatment in greenhouses of regions with water shortage conditions. Also, if the quality of irrigation water is low and it is saline, the use of high amounts of this super moisture absorbent is not recommended.