Effect of Water and Potassium Fertilizer on Yield and Quality of Potato (Solanum tuberosum L.) under Subsurface Irrigation Condition

Drought is the most important environmental stress that limit plant growth and crop production around the world. Long-term tension affects all metabolic processes of the plant and as a result, it often reduces plant production. On the other hand, potatoe is important for dry matter production and dietary intake and has been ranked as the fourth crop for volume of production after wheat, rice and corn. Due to water scarcity, population increase and necessity of more production of this crop, it is necessary to study the effects of water deficit on the yield and physiology and quality of potato. The purpose of this experiment was to investigate the effect of various irrigation regimes by subsoil irrigation at different depths on the potato yield and potassium effects as a damage reducer factor caused by irrigation reduction.

This experiment was conducted in 2014 at Research Farm of Faculty of Agriculture of Ferdowsi University of Mashhad. The experiment was split factorial in a randomized complete block design with three replications. In this experiment, the main plot consisted of irrigation at three levels of 100 percent irrigation (control), 80 percent and 60 percent of the required blueberries throughout the plant growth period and Sub plots consisted of two sub-surface drip irrigation systems in two levels, including drip tape in depth 7.5 cm soil layer and drip tape in depth 15 cm layer of soil and the factor of potassium fertilizer application in two levels, including 100 percent and 120 percent recommended soil test. In this research, Fontaneh, cultivar which has a better adaptability with Mashhad conditions than the other cultivars, were used for growing season and industrial market. Plant water requirement in Mashhad conditions was also determined using software (OPTIWAT). Irrigation volume during growth season to supply 100 percent water requirement was 6840 cubic meters per hectare, for 80 percent was 5742 cubic meters per hectare and for 60 percent was 4104 cubic meters per hectare. Weeding is carried out manually. The measured indexes included number of tubers per plant, tuber mean weight, tuber yield, relative water content of leaves (RWC), dry matter content, electrolyte leakage and chlorophyll content. The data were analyzed by SAS statistical program and the meanings were compared by Duncan test at 5 percent level.

The results of the experiment showed that irrigation have a significant effect on most traits. So that the highest number of tubers in the plant and the relative water content was obtained in the control treatment, namely 100 percent water requirement of potatoes, but percentage of dry matter, electrolyte leakage and chlorophyll were increased with irrigation reduction. There was a significant difference between the two drip irrigation systems in terms of gland performance, and the amount of this trait was higher in the treatment of the drip tape at 7.5 cm depth. The results of this experiment showed that there was no significant difference between two levels of potassium fertilizer in terms of most traits. In general, it can be concluded that although irrigation treatment has a significant effect on most of the studied traits, the trend of changes in the two types of drip irrigation systems used in this experiment is one.

The results of this experiment showed that reduction of irrigation water in the potato whole growth season can have a negative effect on morphological characteristics, yield and yield components compared to the full supply of water. The tuber yield decreases with decreasing irrigation volume, due to the sensitivity of the plant to soil moisture, especially at the time of tuber initiation and tuberization.