Effect of Deficit Irrigation on Water Use Efficiency and Tuber Dry Matter of Potato Cultivars

Potato ranks the first with respect to the amount of energy production per unit area. It is cultivated in about 19.5 million hectares throughout the world and its annual production is about 375 million tons. Iran ranks the third in Asia and 12th in the world in potato production and produces around 4.5 million tons of potato annually. Potato is a sensitive crop to water deficiency and its water requirement is higher compared to many other crops. Due to ever decreasing of water available for agriculture sector and reduced precipitations in recent years deficit irrigation, which results to more efficient use of available water, can be considered as a clever water management strategy in potato production. In this study the effect of deficit irrigation on water use efficiency (WUE) and percent tuber dry matter of 10 potato cultivars were investigated to identify the best performed cultivar (s) under this condition.

A two years study was conducted in a split plot experiment based on complete block design with three replications in Ardabil in 2013 and 2014. The main plot was three levels of irrigation (complete irrigation and irrigation with 80% and 60% of required water) and the subplot consisted of 10 potato cultivars including: Khavaran, Savalan, Luca, Satina, Santae, Marfona, Ceasar, Agria, Aula and Draga. Each plot consisted of 6 rows of 4.5 m long (27 m2). Required water conveyed to the plots through tape line equipped with a measurer gauge. At harvest 7.5 m2 of each plot (excluding the borders) was hand harvested and transferred to the laboratory, where marketable tubers (tubers with at least 35 mm or more in size) were separated and weighted and data were transformed to ton.ha-1. To determine percent dry matter of tubers, a 300 g tuber sample was taken from each plot, chopped to one cm pieces and oven dried at 750C for 48 hours until a constant weight was obtained and then the dry matter was measured.

The analysis of variance result of WUE revealed that there were significant differences between years, irrigation treatments and cultivars. Also, the interactions of irrigation × year and irrigation × cultivar were significant. Water use efficiency were higher in both mild and severe water deficit conditions compared to complete irrigation and there were significant differences among potato cultivars in all three irrigation regimes. Under severe water deficit condition the highest and the lowest WUE were found in cultivars Satina and Marfona respectively (5.88 and 2.24 kg.m-3) and the lowest and the highest percent reduction of WUE were also observed in cultivars Satrina (+50%) and Marfona (-29%), respectively. The effect of water treatment on percent tuber dry matter was not significant. However, significant differences were observed among the potato cultivars in this regard. The highest and the lowest mean percent tuber dry matter were observed in cultivars Savalan (23.6%) and Draga (18%), respectively.

Based on the results obtained in this study it can be concluded that deficit irrigation results in increased WUE especially in cultivar Satina, but has no effect on percent tuber dry matter. Therefore, in regions with severe water limitation cultivar Satina, that has the highest WUE, can be recommended. In regions where enough water is available and higher dry matter is demanded specially by processing industries cultivar Savalan is recommended based on its higher dry matter.