*3.4. Nitrogen Productivity*

Nitrogen productivity refers to the yield per applied N fertilizer (ton kg−1). This value also implicitly depends on the interaction of the given water dose to the fertigation and, as a result, the harvested yield (Figure 4). The main nitrogen addition was due to fertigation and therefore the F0% treatments are not included in Figure 4 due to uncertainty regarding the release dynamics and concentrations of soluble nitrogen from the soil-compost solid phase. Nitrogen productivity decreases with an increasing water dose, which indicates an efficient usage of nitrogen fertilizer. Similar to the results for water productivity, Figure 4 shows that much more nitrogen was applied as compared to the yield with increasing water dose.

**Figure 4.** Nitrogen productivity (ton kg−<sup>1</sup> N) as a function of irrigation and fertigation regime. Values with the same letter are not significantly different (*p* < 0.05).
