*3.7. Nitrogen in the Petioles*

The petiole N-NO3 concentration is a common indicator for plant N demand and the available nitrogen from fertilization [33]. We used this metric to better understand nitrogen uptake and demand during the season and thus to monitor the effect of different N regimes. From the multivariate analysis of the petiole nitrogen, we found that, for a given N treatment, there was no significant difference in petiole nitrogen between the water doses. Thus, in Figure 6 the results are the means from the four water treatments at a given nitrogen treatment (i.e., 16 replicates). It can be seen for all the treatments that petiole nitrogen concentration increases with increasing plant size until it reaches a maximum at DAS = 85. After that stage until harvest, there is a decrease in petiole nitrogen concentration, likely due to resource translocation for tuber development. There is a clear difference between the fertigation doses; the higher the fertigation dose the higher the petiole nitrogen concentration in all five sampling events. This is particularly marked for the F100% treatment compared to the F50% and F0% treatments.

**Figure 6.** N-NO3 in petioles during the growing season.
