**1. Introduction**

Potato (*Solanum tuberosum* L.) growth is characterized by a high demand for nitrogen fertilizer due to its necessity for proper plant and tuber development [1–3]. However, due to a shallow (approximately 30 cm) and inefficient root system, applied water and fertilizer is at risk of leaching below the root zone [4,5]. Although potatoes have a relatively high value, fertilization costs might negatively affect their profitability [6,7]. Therefore, one needs to adjust nitrogen and water availability to crop demand in order to maximize yield, tuber quality, and nitrogen productivity [8–10].

The potato growing season in Israel is from autumn (September–November) to late spring (May–June). The growing area is about 16,000 ha with annual production of approximately 650,000 ton/year. Most growing areas are found in the western Negev region (about 75%); about 20% are located in the center and the remainder in the Galilee and Arava Desert. Whilst appropriate areas for growing potatoes are available in the Arava Desert, there is a shortage of irrigation water and the supply needs to be ensured throughout the growing season. Additionally, the quality of

the irrigation water available for potato growth in this region is low due to its relatively high salt content (2–4 dS m<sup>−</sup>1). This presents a real obstacle to the use of sprinkler irrigation—commonly considered as the best irrigation technique for potatoes [11]. Moreover, due to the low irrigation efficiency of sprinkler irrigation (about 75%), there is a loss of water and leaching of mobile nutrients. These inherent inefficiencies clearly lead to very low recoveries of applied fertilizers as well as the possibility of groundwater contamination.

In Israel, potatoes are usually grown on sandy soils, which have low water and nutrient holding capacity, thus increasing the risk of nitrogen loss by leaching under excess irrigation [12,13]. Thus, an alternative practice should be adopted in such areas and especially in arid areas where water resources are limited.

The use of drip irrigation and fertigation may be the solution. The employment of dripper discharge lower than 0.6 L h−<sup>1</sup> has been recently demonstrated as an efficient method for potato growth in an arid region [14]. Due to low discharge and precise water application, drip irrigation reduces groundwater contamination, water and fertilizer waste, and energy inputs [15–17]. Surface or subsurface drip irrigation enables high water and oxygen availability in the root zone due to partial wetting [18]. Because of high soil-water pressure head and hydraulic conductivity in the root zone, water and nutrient availability is increased [19,20]. By minimizing the seepage losses beneath the shallow potato root zone, water and nitrogen productivity can be increased [21,22]. However, in the long term, one should monitor and prevent the accumulation of salts in the root zone, especially in arid areas where precipitation is almost negligible [23–25].

In areas where fertigation is applied, it is important to take into consideration the dripper discharge, the spacing between drippers, and soil hydraulic properties in order to achieve the optimal water content [26–29] and nitrogen availability [30] in the root zone.

Increasing water productivity (i.e., the volume of irrigation water required for a desired yield) is currently one of the main goals in arid and semi-arid regions [31,32]. Recently, Trifonov et al. [14] suggested that higher water productivity in potato crops could be achieved in the Arava Desert by using low-discharge drip irrigation. In their study, the combination of emitter discharge (0.6 vs. 1.6 L h−1), spacing (25 vs. 50 cm) and irrigation dose (40, 50, 60, 80, 100 and 120%; where 100% was approximately 620 mm) was examined. In terms of tuber yield, it was found that a combination of sprinkler irrigation for germination (approximately 100 mm) and low discharge drip irrigation produced potato yields similar to the ones obtained from sprinkler irrigation, without harming tuber marketability (i.e., size and quality). The results suggested that the 80% irrigation dose is sufficient for optimal tuber yields and that discharge of 0.6 L h−<sup>1</sup> is applicable for dripper spacing ranging from 20 to 50 cm. In terms of water productivity, it was demonstrated that the lower the irrigation dose the higher the water productivity.

Following the insights from our previous study [14], we further examined the influence of the irrigation water dose in conjunction with three nitrogen levels on potato growth in the Arava Desert. Hence, the main objective of this study was the optimization of potato growth under a low discharge drip irrigation and fertigation regime.
