Effect of super absorbent polymer on quantitative and qualitative traits of cowpea (Vigna unguiculata L.) in low irrigation management conditions

Beans are the major part of the diet of many people in the world, because the large amounts of protein in combination with cereal grains could provide a valuable source of food. Iran is located in dry and semi-arid region, and water deficit due to the drought are observed in most parts of Iran. Therefore, implementation of irrigation techniques in order to be more productive than water resources is a scientific approach to reducing water consumption. Meanwhile, based on research, the use of super absorbent hydrogels can increase the yield or reduce the damage caused by scarcity of water resources. Accordingly, this experiment was conducted to investigate the effect of super absorbent polymer under low irrigation conditions on quantitative and qualitative traits of cowpea.

This research was conducted in summer 2015 in a field located 12 Km far from Ahvaz. This experiment was carried out as strip-plot in a randomized complete block design with three replications. The first factor consists of: 1) furrow full irrigation (control), 2) fixed alternate furrow irrigation and 3) variable alternate furrow. The second factor included three levels of super absorbent polymers: 1) Absence of super absorbent (control), 2) 75 Kg/ha and 3) 150 Kg/ha. Super absorbent on the basis of treatments was mixed with the soil with the help of a disk machine. Stagger furrow irrigation is one of the irrigation methods which can be applied fixed or alternatively by irrigation of half of the furrows. In the irrigation of variable alternate furrow, the furrows are irrigated as arrange in a series of alternating intervals. That way, in one irrigation time, two furrows and in next irrigation time, only the middle furrows is irrigated. In this method, only half of the plant roots, tolerate a period of drought stress and in the next irrigation, the dry period is removed and the other half is subjected to drought stress.

The results showed that the differences between different levels of irrigation was significant in number of pods per plant, number of seeds per pod, 100-seed weight, protein percentage, grain yield, biological yield and harvest index at 1% probability level. The effect of different levels of super absorbent on all tested traits was significant at the level of probability of 1% and grain protein content at 5% level. The interaction between different levels of irrigation and super absorbent on number of pods per plant and harvest index was significant at 5% probability level. The maximum grain yield under furrow full irrigation and 150 Kg/ha super absorbent were 2853.4 and 2314.5 Kg/ha, respectively, and the minimum grain yield under fixed alternate furrow irrigation and absence of super absorbent was obtained were 1108.2 and 1453.2 Kg/ha, respectively. It has been stated that the beans are sensitive to water shortages throughout the growth stage and water shortages, especially during flowering stage and grain filling period, can reduce grain yield. The role of super absorbents in increasing the grain yield can be attributed to a better supply of water and nutrients and the availability of them during stress and also to the reduction of water and nutrients waste. The maximum percentage of protein under fixed alternate furrow irrigation and absence of super absorbent was 28.89% and 27.58%, respectively, and the minimum percentage of protein was observed under furrow full irrigation and and consumption of 150 Kg/ha super absorbent was observed with 22.57% and 24.08%, respectively. It has been stated that drought stress increased the protein percentage of seeds relative to normal irrigation conditions. The reason for reduction of protein is to reduce the transfer of photosynthetic material to the seeds. Because, the percentage of protein in the shell and embryo is higher than endosperm. Therefore, in water shortage conditions due to reduction of transfer of photosynthetic material to endosperm, the seed protein percentage is increased compared to endosperm. Super adsorbents create better conditions for water absorption. This increases the photosynthetic capacity and storage of carbon hydrates in the seeds and decreases the protein content.

In general, the results of the experiment showed that the effect of super absorbent application in furrow full irrigation conditions with increasing production parameters and under low irrigation conditions, with reducing the effects of water deficit and improving the damage caused by it, could be effective in increasing the yield. However, with the use of super absorbent, the yield qualitative was reduced