Improving water use efficiency, estimating economic benefits and increasing potato tuber quality by the combined application of super absorbent polymer and mycorrhizal biofertilizer

Potato is a sensitive crop to drought stress, especially in the stage of tuber formation. Correct management of irrigation in the field has an important role in increasing the water use efficiency; and by preventing yield reduction, the amount of disease contamination is reduced and the quality of the tuber production is also improved (Wilson et al., 2001; Johansen et al., 2015). Given the limited annual rainfall in Hamedan province (averaging 310 mm) and its poor distribution, combined with the potato's high water requirements, agronomic methods are essential for preserving and sustaining production. In this regard, uagae of superabsorbent materials and inoculation with mycorrhizal biofertilizers are suitable tools for water management, as these materials increase the competitive power of the potato crop by creating the desired growth power. They can lead to a quantitative and qualitative increase of the product by creating more favorable growth and avoiding stress during the critical stages of growth. Limited research has been done on the effect of superabsorbent materials and mycorrhiza, especially in deficit irrigation of potatoes. There are very few reports on the effect of combined application of superabsorbent and mycorrhiza in potato crop. Therefore, this experiment investigated the effects of separate and combined applications of superabsorbent materials and mycorrhizal biofertilizers on water use efficiency, potato yield, and tuber appearance quality (deformity and scab infection index) under low irrigation conditions.

Experimental model The experiment employed a Strip Factorial design nested within a Randomized Complete Block Design (RCBD) with three replications. Irrigation levels were manipulated in horizontal plots, with treatments including 100%, 75%, and 50% of optimal water requirements based on the Penman-Mantith evapotranspiration formula. The second factor involved four levels: control, superabsorbent and mycorrhiza seperately, and a combination of both, arranged as sub-plots. The Agria potato cultivar was used for the study.

Verification of the physical model:

Superabsorbent material named Trawat200A was applied at 80 kg per hectare directly to the tubers at planting time. The tubers were also inoculated with mycorrhizal inoculum containing 120 CFU/g of active propagules. Irrigation commenced at the beginning of the growing season, immediately following planting. Irrigation amounts were determined using the modified Penman-Mantith formula, adjusted for 90% irrigation efficiency. Yield was assessed at harvest by randomly selecting two 1-square-meter plots within each replication and treatment.

Dimensional analysis:

the harvested tubers were divided according to their size into three sizes groups (smaller than 35, 35 to 55 mm, and larger than 55 mm), weighed and counted. The number of deformed and malformed tubers with secondary growth as well as decayed tubers were counted and weighed in different treatments. The effect of treatments on the percentage of tubers infected with common scab disease was investigated using Hao et al.'s method (Hao et al., 2009).

Variance analysis of the data demonstrated that irrigation levels, mycorrhizal biofertilizer, and their interactive effect were significantly influential (p ≤ 0.01) on the number of tubers categorized by size (seed, edible, and small), the scab disease infection index, tuber dry matter percentage, and water use efficiency.Secondary growth in potato tuber influenced by the simple effect of irrigation treatment at the probability level of 5% (p≤0.05). Irrigation treatment had a significant effect (p≤0.01) on the amount of tuber dry matter and total yield. Using of superabsorbent and mycorrhiza affected the performance at the level of 1% (p≤0.01). The number of large tubers increased at different irrigation levels and with separate and combined application of mycorrhiza and superabsorbent compared to the control treatment. Using of mycorrhizae and superabsorbent and also their combination increased the yield compared to the control treatment in all three irrigation levels. Nevertheless, only in combination treatment a significant difference was created. Phosphorus is a critical element for plant metabolism, particularly in carbohydrate processes. Moreover, mycorrhizal fungi excel at phosphorus absorption, especially under water-stressed conditions. This can be a convincing reason for increasing the dry matter of the plant and as a result the dry matter of the tubers under the conditions of using mycorrhizal biofertilizer. Based on other published data from this research (Parvizi et al., 2022), it was determined that the separate application of mycorrhiza and the combined application of mycorrhiza and superabsorbent had a significant effect on phosphorus uptake in potatoes compared to the superabsorbent and control treatments in all three irrigation levels. These positive effects of mycorrhiza on phosphorus uptake and its increase in the foliage and ultimately the potato tuber were directly related to the severity of water stress and were highest in the 50% irrigation requirement treatment. The amount of secondary growth in the tubers was directly related to the reduction of irrigation. So the control treatments had the highest amount of secondary growth in the tuber at two irrigation levels of 50 and 75%. However, with the use of mycorrhizal and superabsorbent biofertilizers, the amount of secondary growth in these irrigation treatments was greatly reduced. In two irrigation levels of 75 and 50%, separate application of superabsorbent and mycorrhizal biofertilizer, and their combination were able to significantly reduce the intensity of scab contamination index. Of course, these reduction effects were more significant in their combined application. In total, in all three irrigation treatments, the combined effects of superabsorbent and mycorrhizal biofertilizer were more effective in reducing scab than their separate application.

The positive effects of mycorrhizae and superabsorbent were more evident in increasing tuber dry matter, reducing secondary growth and tuber deformity, as well as reducing the rate of infection with scab disease in conditions of severe lack of irrigation. In total, the water use efficiency with the use of mycorrhiza and superabsorbent in both low irrigation conditions (Irrigation treatments at 50% and 75% of potato water requirements) increased significantly compared to the control treatment.