*3.1. Water Inputs and Outputs*

The impacts of water restriction on potato production will likely increase over the next decades due to climate change. Alternatively, areas that were not previously considered as arid may undergo desertification, thus forcing farmers to adapt to new conditions. Therefore, there is a need for a suitable irrigation regime as well as knowledge of soil properties. Each soil type has its own properties that will indicate the water availability to the crop. Based on the field capacity and wilting point of the soil in our study, the available soil water storage was approximately 8%. Specifically, a bed width of 0.9 m and active root zone of 0.3 m allows for an estimation that the available water (storage) is approximately 22 mm. Assuming that this is the case for all treatments, it makes up about 10% of the low irrigation dose (i.e., 40%) and about 4% of the higher dose (i.e., 100%). Note that the net contribution of rainfall to the water balance was negligible (about 32 mm) as the differences in water storage between the beginning and end of the growing season were small. Specifically, the mean precipitation in the study area is about 30 mm/year, distributed over 5 to 10 rain events (e.g., Figure 1). Considering the potential evaporation in the study region (i.e., approximately 5 mm/day), clearly the rain contribution on a daily basis is negligible. The above precipitation level and distribution is common to the study area [14] and, consequently, the rain contribution to the total water balance. Consequently, the potato growth in this area is entirely dependent on the supplied irrigation and fertigation. The actual irrigation dose corresponded well to the planned doses as can be seen in Table 2, with the average deviation from the planned dose being <1%. The actual 100% irrigation dose was about 545 mm; together with the germination dose (100 mm), the total water applied was 645 mm, comprising about 80% of the cumulative potential evaporation during the growing season (787 mm—Figure 1).
