Effect of A200 super absorbent polymers on corn growth and yield under Partial Root-Zone Drying Irrigation

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Introduction

With an average precipitation of 250 mm per year, Iran is considered of the arid and semi-arid areas of the world (annual average precipitation in Asia is almost 600mm and in the world 840 mm). About 90% of this amount is used in agriculture section. Water waste in Iran agriculture is unfortunately more than global average; based on existing reports the rate of water waste in the country is 28 to 30% while this amount of waste in the world is reported as 9 to 12% (Tardio, 2005).

In terms of climate, Iran is located in arid and semi-arid area. given the high need of the country to supply food for the growing population and the necessity of more attempt to achieve self-sufficiency in agricultural production and also because water is the first and most important limiting factor in increasing agricultural products, water problem and its exploitation are of particular importance (Alizadeh et al. 2009).

Maize cultivation has a close compliance with arid and semi-arid areas in the world due to its particular features such as being C4 and especially high temperature tolerance. In arid and semi-arid areas, the ideal conditions to produce high yield of this plant can be supplied with adequate moisture. Having appropriate weather diversity, Iran is of the prone areas for producing maize while two third of farming lands in Iran are located in semi-arid areas, practically facing with drought stress. Water shortage affects the growth and allocation of dry material and grain yield during each phase of maize growth but the rate of damage depends on time of stress, intensity and duration of water shortage (Lak et al. 2006). Maize (Zea mays L.) has been expanded all over the world due to ideal features and is ranked as third cultivation level after wheat and rice, which has been increasing in Iran over the recent years (Nourmohammadi et al. 2001). Providing ideal conditions, especially sufficient water in growth period, in arid and semi-arid areas is a serious problem. Since water shortage is one of barriers in successful production of this product, numerous studies have been conducted about the reasons of grain yield reduction in moisture stress conditions (Stear et al. 2001).

One of the most important and effective solutions of coping with water crisis is optimum use of water in agriculture. In other word, increasing “agricultural water productivity” is unavoidable in future planning and decision making as an effective factor. Therefore, deficit irrigation is stated as a proper solution in water limitation aiming to maximally use water volume unit. Deficit irrigation isn’t a method of irrigation but it is considered as a kind of efficient and dynamic management of exploitation, will majorly affect water resources management and ultimately agriculture economy (Kapsis et al. 1989).

In addition to applying irrigation management methods, to save soil moisture and consequently increasing irrigation efficiency, developed techniques such as using super absorbent polymers can be used. Super absorbent is a hydrophilic polymer with a three dimensional grid, capable of absorbing and maintaining high amount of water and water solutions (Behbahani et al. 2005). These materials absorb and maintain water several times its own weight and as the result of environment dryness, the water inside polymer is gradually evacuated. Therefore, soil is remained wet for a long time without irrigating again (Woo et al. 2008). Of the other advantages of super absorbent, increasing water penetration in soil, soil structure sustainability and reducing soil erosion, reducing the rate of evaporation from soil surface, increasing water use efficiency, increasing germination strength, increasing plant yield and reducing the need of irrigation water can be mentioned (Lentez et al. 1998, till and Alhadi, 1981). These properties are of great importance for coping with low water conditions and reducing the dangerous effects of drought stress on plants.

In the arid areas, facing shortage of irrigation water for farming, super absorbent hydrogels can operate as soil amendment to increase water inside the soil and prevent water deficiency and also cause faster and healthier growth of plants especially in very hot and dry areas.

Ghasemi and Khoshkhoy (2007) evaluated the effect of super absorbent polymer on irrigation and growth of Chrysanthemum according to the indicators of flower number, flower diameter, wet and dry weight of flower, leaf number, leaf surface, shoot wet and dry weight, the number of branches, plant length, wet and dry weight of root, the ratio of root to the shoot and the ratio of surface in drought stress conditions in all indicators except the ratio of root to the shoot; the most means were related to treatment of 8gr polymer in 2-day irrigation period. In the treatments of 1 to 6gr polymer in 4-day irrigation, the means didn’t have significant difference with control one (without polymer) in 2-day irrigation. Investigating the effect of root partial deficit irrigation and ordinary deficit irrigation of maize on nitrate absorption and leaching potential, Karandish et al. (2012) showed that reducing the depth of irrigation water significantly reduces leaf nitrogen and total saved nitrogen in aerial organs in the treatments of DI75, DI55 and PRD55 at the level of 5% but this difference wasn’t significant between treatments of FI and PRD75. The rate of product yield in treatments of DI55, DI75 and PRD75 were less than FI treatment respectively as 54, 52 and 17% in 2010 and 26, 14 and 20% in 2011. This difference wasn’t significant between treatments of FI and PRD75. As a conclusion, they stated that PRD75 method, for maintaining both environmental and economic issues, is considered as an appropriate solution to achieve sustainable agriculture.

The results of investigating the effect of super absorbent on sugarcane growth show that using 15-25kg super absorbent per hectare reduces the amount of irrigation for 50% and increases the amount of product and produces pure sugar for 10 to 30%. The application of super absorbent in maize increases the product yield, improves the effectiveness of nitrated fertilizer and increases Biomass production compared to the control group. It was also identified that using super absorbent increases growth pace uniformly from germination to full maturity of product. The application of dry super absorbent (micro) as 10-15kg/hectare simultaneously with cultivating the seed in rain-fed and irrigated wheat cultivation not only increases water efficiency but also increases plant establishment and yield due to providing favorable conditions for germination (Naderi and Farahani, 2006). The results of studies show that by promoting and improving the status of soil aggregates, maintaining soil structure, reducing soil apparent specific weight, increasing and strengthening porosity status, providing soil moisture, increasing soil penetrability and increasing the rate of water penetration in the soil, super absorbent polymers reduces or even stops erosion and runoff. High capacity of polymer water absorption leads to pores more increase and capillarity effect (Zeinoaddin and Aldakhel, 2006).

Given Iran's climate and lack of rainfall and its proper distribution in farming season, the current study has been conducted to investigate the effect of super absorbent polymers as an ideal and developed management method for optimum use of precipitation, soil moisture maintenance to increase irrigation efficiency and as the result improving water limited sources exploitation.

Materials and Methods

Given the mentioned information based on the importance of promoting water use through management methods and also using developed techniques, this study was conducted during two farming seasons of 2014 and 2015 in research farm of Sari Agricultural Sciences and Natural Resources University on single cross 704 silage maize. The soil of experiment location was of clay loam type and its physicochemical properties have been shown in Table 1.

Table 1. The properties of experiment location soil.

To implement the plan, split-plot was used in the form of complete randomized blocks, in which three irrigation regimes (as the main plot) and three levels of super absorbent (as sub-plots) with three replications. Irrigation treatments include complete and partial root deficit irrigation at two levels of 55 and 65% (PRD65, PRD55) and three levels of water super absorbent polymer of A200 type, including 0, 30 and 60kg/hectare, the physicochemical properties of which have been shown in Table 2.

Table 2. Physicochemical properties of A200 super absorbent polymer.

Cultivation was performed in the middle of May and the row space in maize cultivation 75cm, plant space in the row 20cm and the length of cultivation rows is 7 m.

Water need of complete irrigation treatment was calculated based on equation 1. In partial root irrigation, 55% and 65% of water need, calculated in complete irrigation, were applied (Chk, ilhvhkT,2004).

In which; In is water need in millimeters, Ѳ_Fc is the volume percentage of farm farming capacity, Ѳ_w is the volume percentage of soil moisture before irrigation, D_i is the depth of each layer in millimeters and also i is the number of each soil layer.

To provide water need of plant, drip tape irrigation system was used. In partial root irrigation, two laterals were set on both sides of cultivation row in the space of 20cm of each cultivation row on the ground, that in each time of irrigation, water flew periodically only in one of them to be ensured of dryness of other side of root. In complete irrigation, there are also two lateral pipes on both sides of cultivation row which both simultaneously irrigated in these treatments. To measure soil moisture and determine irrigation time, electromagnetic moisture meter (TDR) was used. Irrigation was conducted aiming to moisturize root according to the farming capacity. The volume of irrigation water was also measured for each one of treatments by contour.

To investigate the variations and methods of moisture distribution in soil, three pipes of 1 meter of TDR device were installed vertically on cultivation row and between two laterals (in depths of 20 cm spaces) in the ground. To this end, moisture data in the 20cm depths scope on cultivation row and between drip tape and cultivation row were daily read and noted. Irrigation interval was also considered fixed as 2 days.

The rate of irrigation water use efficiency index (IWUE) was also calculated for different treatments from equation 2.

In which Y is equal to product yield and In is the net depth of irrigation which were calculated from equation 1.

During growth period and after applying the treatments in four phases, the leaves surface, wet and dry weight of stem and leaf were measured. To determine grain yield and biological yield at the end of growth season, the middle rows were sampled through eliminating side, beginning and ending rows of each plot and total weight of aerial organs was measured using digital scale. Leaf, stem and grain samples related to each treatment in paper covers were separately put in the ventilated oven at 70 ° C for 72 hours. Then sample dry weight was measured by digital scale. The data were analyzed in SAS9.1 software in factories arrangement based on complete randomized block and the means of treatments were compared through LSD test at 5% level. The diagrams were drawn in EXCELL software.

Results and Discussion

The obtained results of variance analysis showed that main effects of irrigation levels and the application of super absorbent were significant on the ear diameter traits, ear length, ear weight, tassel weight, ear leaf area, the number of ear, grain number in ear, thousand weight, biomass, total yield per hectare and cultivation index (Table 3). So that the plants, irrigated controlled and at the right time during their growth period, and also the ones, in cultivation of which 60 kg/hectare of super absorbent was had been used, had the most rate of study traits (Table 4). The results of researches (Checker, 2004) about applying moisture stress in different phases of maize growth show that moisture stress in ear silk and formation phase reduces grain yield severely. Applying moisture stress in growth stage will also decline 28-32% of produced dry material.

Table 3. Analyzing the variance of irrigation and super absorbent effect on maize yield and yield components.

Table 4.  Comparing the mean of irrigation levels and super absorbent effect on maize yield traits.

This yield reduction in case of stress treatment during flowering, due to drying of upper leaves and male flowers, causes disorder in grains inoculation and reduces the yield. In stress treatment when grains are filling, it leads to appearing shrunken grains with less weight through direct affecting current photosynthesis of the plant and reduction of assimilates amount and also because of prematurity physiologically, it shortens the length of grains filling period.

Allahdadi and Moazenghamsari (2005) investigated the effect of four A200 super water super absorbent polymer (zero, 100, 200 and 300kg/hectare) and three irrigation intervals (5, 7 and 9 times a day) on single cross 704 silage maize growth and yield under farm conditions. Their experiments showed that increasing the height and yield of maize is obtained using high values of super absorbent. They also reported that there is no significant difference between the product of 3-day irrigation interval without polymer and 7-day irrigation interval with 200kg/hectare polymer. In a research with the application of Polyacrylamide Polymer in cultivation environment of philodendron, Jandaghian (1996) showed that by increasing the value of polymer from volume zero to 50%, plant length, leaf number, leaf surface, wet and dry weight of shoot and root dry and wet weight will increase. Ghasemi and Khoshkhoy (2007) showed in their study that using super absorbent polymer has a positive and significant effect on the indicators of leaf number and leaf surface in dry stress conditions.

Given the importance of water use efficiency, Todler (1993) reported that using anionic Polyacrylamide Polymer in sand and loam soils increases water maintenance. Taylor and Halfaker (1986) also reported that new leaf growth in improved hydrophilic polymer and hydrophilic polymers need far less irrigation than those, have been cultivated in the environments without polymer. In other study, Haterman et al. (1999) observed that by increasing the values of hydrogel super absorbent, water maintenance in soil is increasingly enhanced and after stopping irrigation, the lifelong of treated Pinus halepensis plants with 4% is two times of control treatment.

The obtained results of analyzing variance of mutual effects of irrigation and super absorbent showed that mutual effects of irrigation levels and the application of super absorbent had significant effect on the traits of ear diameter, ear length, ear weight, ear number and cultivation index (Table 5 and Table 6).

Table 5. Comparing the means of mutual effect of irrigation levels and super absorbent on ear diameter, weight, number and cultivation index.

Table 6. Simple correlation coefficients of maize yield components.

According to the obtained results of plants, irrigated regularly during their growth period and cultivated in the conditions of 60 kg/hectare of super absorbent, had the most rate of yield traits but they did not have significant difference with the plants, irrigated with volume 55 and 65%. In other word the function of super absorbent in these treatments increased the efficiency of water use and partial irrigation in 55 and 65% volume has been able to generate an equal yield with the conditions of complete irrigation. Super absorbent saves water and improves physical conditions and probably appropriate accessibility to nutrients and increases the dry material yield through saving water and releasing it at the right time.

The means, having similar letters in one column are significantly different from each other based on Duncan multi-thread test at confidence level of 5%.

Conclusion

The conducted studies have shown that super absorbent polymers increased plant’s accessibility to moisture and as the result improved irrigation efficiency through absorbing and maintaining irrigation water and releasing it gradually. Given Iran's climate and lack of rainfall and its proper distribution in farming season, using super absorbent polymers is recommended as an ideal and developed management method for optimum use of precipitation, soil moisture maintenance to increase irrigation efficiency and as the result improving water limited sources exploitation. Super absorbent in soil absorbs water with its soluble fertilizers and gives it to the root in case of demand. So this method alone or beside other new methods of irrigation, in case of being implemented and continued correctly, can promote Iran agriculture.

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