Effect of Water Regime, Nitrogen Level, and Biostimulant Application on the Water and Nitrogen Use Efficiency of Wild Rocket [Diplotaxis tenuifolia (L.) DC]

The use of biostimulants in agriculture is an emerging technique that can contribute to improved production and resource use efficiency. This research was carried out in southern Italy to evaluate the biostimulating effects of seaweed extract (SW) and azoxystrobin (AZ) on wild rocket subjected to two water regimes (WRs) and three nitrogen levels (NLs), and grown in pots under unheated greenhouse conditions. The following treatments were compared: (i) two WRs: restoration of 100% (WR100) and 50% (WR50) of crop evapotranspiration; (ii) three NLs: 0 (N0), 75 (N75), or 150 (N150) kg ha−1 of N; and (iii) three biostimulants (BSs): an untreated control (C), and the application of AZ or SW. This paper reports the effects on N uptake (Nup), N use efficiency (NUE), and water use efficiency (WUE). The following indicators of NUE were assessed: apparent recovery efficiency (RE), internal utilization efficiency (IE), partial productivity factor (PFPn) of N supplied, agronomic efficiency (AE), and physiological efficiency (PE). The following indicators of WUE were assessed: photosynthetic WUE (p_WUE), yield WUE (Y_WUE), biomass WUE (B_WUE), and irrigation yield WUE (IY_WUE). The indicators of NUE were affected differently by treatments. RE was 20% higher with SW. IE was higher with AZ. PFPn increased by 10.4 and 8.1% with AZ and SW, respectively. AE increased by 10.9 and 19.9% after applying AZ and SW, respectively. PE rose by 6.7 and 9.3% after applying AZ and SW. AZ and SW improved p_WUE, mainly under water deficit (interaction of WR × BS). With AZ application, Y_WUE, B_WUE, and IY_WUE were higher by 17.8, 13.8, and 19.3%, respectively, while the application of SW resulted in a smaller increase (9.5–7.7 and 9.9%). SW and AZ were shown to be effective through the moderate improvement of wild rocket’s nitrogen and water use efficiency. The two biostimulants were more effective at improving p_WUE in water deficit conditions, proving to be particularly useful for farmers operating with water scarcity. Therefore, they can provide valuable support to farmers by improving the sustainability of resource use.