Evaluation the of the Effect of Application of Superabsorbent and Mycorrhiza Inoculation on Nutrient Uptake, Water Use Efficiency and Yield of Potato (Solanum tuberosum) Plant in Deficit Irrigation Conditions

Hamedan province, characterized by an average annual rainfall of less than 340 mm, faces significant limitations in potato production)Solanum tuberosum(, primarily due to the scarcity of irrigation water and the occurrence of drought stress during critical growth stages. In order to address these challenges, the utilization of aqueous superabsorbent materials and the inoculation of mycorrhizal fungi have emerged as highly suitable approaches. These methods aim to optimize the utilization of water and soil resources (Khadem et al., 2011). Previous studies have indicated that the inoculation of arbuscular mycorrhizal fungi in various plant species, apart from potatoes, can reduce the impact of drought stress and enhance nutrient uptake (Bolannazar et al., 2007; Subramanian et al., 2008). However, limited research has been conducted on the effects of superabsorbents and mycorrhizae, particularly under conditions of moisture stress and deficit irrigation in potato crops. Consequently, this experiment aims to investigate the effects of applying these methods under stress conditions.

The experiment was arranged in strip factorial based on randomized complete block design with three replications. Three irrigation levels containing optimal irrigation (100, 75 and 50% of water requirement based on evapotranspiration from Pan Class A) in horizontal plots and factor 2 using Trawat200A superadsorbent (0 and 80 kg.ha-1) and four mycorrhiza and superabsorbent levels including no application of these material (control), superabsorbent, mycorrhiza as a bio-fertilizer and their combination were considered as sub plots. The Agria potato cultivar was selected. Superabsorbent material was applied adjacent to the tubers at planting time. Mycorrhizal inoculum containing the active propagules (CFU 120 /g) was inoculated to the tubers. The concentration of nutrients in the shoot and in the tubers were determined by using Kjeldahl apparatus for Nitrogen (Waling et al., 1989), spectrophotometer for phosphorus (Jones, 2001), flame photometry for Potassium and atomic absorption spectroscopy for Iron, Zinc, and Manganese (Ryan et al., 2001). the produced tubers were divided, weighed and counted based on their size in three groups (small, medium and larg). Water use efficiency was determined as the amount of dry matter produced per cubic meter of water consumption in different treatments.

The results of combined analysis of variance showed that the main effects of irrigation rate, application of mycorrhiza and superabsorbent on tuber yield and percentage of dry matter, nutrient uptake in stem, leaf and tuber were significant. Comparison of means showed that with the application of low irrigation and increasing the intensity of water deficiency (reducing the amount of irrigation water), total yield decreased, but this decrease was significantly less in conditions of inoculation with mycorrhiza and the use of superabsorbent polymer. Mycorrhiza and superabsorbent increased the absorption of nutrients, especially under severe water deficiency. In this study, there was a significant difference in the uptake of phosphorus and other low-consumption and high-consumption nutrients at normal irrigation levels and stress in mycorrhizal plants, so that their uptake increased in proportion to the increase in stress intensity and in mycorrhizal inoculation conditions. It seems that by creating stress conditions, the ability and efficiency of mycorrhiza in nutrient uptake is increased and thus in the conditions of lack of moisture with the coexistence mechanism in the relationship of the plant more effectively helps the survival and durability of the plant. Mycorrhizal fungi can increase the uptake of phosphorus from the soil by increasing the relative water content and ultimately play an effective role in increasing plant growth (Krishna et al., 2005). In this study, it was found that the use of superabsorbent in potatoes helps to increase the absorption of nutrients. The reason for this can be increasing the storage capacity of water and nutrients for a long time in the soil, reducing nutrient leaching, rapid and optimal root growth with better nutrient storage and aeration of the soil.

In this study, it was found that the application of superabsorbent and mycorrhiza in potato helps to increase nutrient uptake as well as tuber yield. The positive effects of combined application  of mycorrhiza and superabsorbent on nutrient uptake and yield were more evident especially in conditions of severe water deficiency.
Acknowledgements
We are grateful for the efforts of Dr. Bakhtiari and Mr. Abdolreza Mordai in coordinating and equipping irrigation equipment and land preparation.