*2.3. Sampling and Analysis*

Each replicate consisted of three rows and, to avoid edge effects, only the middle bed was sampled. During the growing stage, five samples (DAS = 58, 71, 85, 99 and 113) of petiole nitrate-N concentration were taken. The sampling was performed on fully expanded youngest leaves on the main stem, typically fourth or fifth from the top, from three different plants [33]. The sampling was performed at 7 to 14 day intervals [34]. At DAS = 152, the potato yield was assessed on collected tubers from an approximately 2 m<sup>2</sup> area (2.2 m by 0.9 m). The yield from all four replicates was pooled and weighed. In addition to this, two random replicates from each treatment were selected and the following data were collected for about 1600 tubers: Tuber length, tuber width, tuber mass, and their total number. The tuber qualitative evaluation included dextrose concentration and percentage of total solids. The soil, both above (0–5 cm) and beneath (5–20, 20–40 and 40–60 cm) the drippers, was sampled at the beginning and end of the growing season. These samples are referred to later as 5, 20, 40 and 60 cm, respectively. Chemical analyses (EC, Cl−, dissolved organic carbon (DOC), total nitrogen (TN), NO3 −, and NH4 +) were performed on 1:1 soil:double distilled water (DDW) extracts.
