Effects of Green Manure, Leaf Cutting Height and Harvesting Date on Yield, Quality, Nitrate Accumulation and Elemental Composition in Wall Rocket (Diplotaxis tenuifolia L.)

Optimizing cultivation practices for leafy vegetables is essential to ensure food safety and environmental sustainability, particularly due to nitrate accumulation in edible tissues. This study aimed to evaluate the effects of Sudanese grass (Sorghum × drummondii) used as green manure and different cutting heights at harvest on yield, growth, and leaf quality of wild rocket (Diplotaxis tenuifolia (L.) D.C.), with a focus on nitrate content. The experiment was conducted during the 2021–2022 growing season under a polyethylene tunnel in southern Italy. A strip-plot design with three replications was adopted, comparing Sudan grass green manure incorporation (12.6 t ha−¹, C/N ratio 29.71) with an untreated control and two cutting heights (3 cm and 6 cm). Crop performance was assessed over four successive harvests by measuring fresh and dry yield, leaf nitrate concentration, mineral composition, and organic acid content using ion chromatography. Green manure application did not significantly affect wild rocket yield or leaf nitrate concentration. Increasing cutting height from 3 cm to 6 cm reduced marketable yield by 35.7%, while leaf nitrate content decreased on average by 13.6%. At the 6 cm cutting height, leaf nitrate concentration showed a weak negative correlation with soil nitrate content. Adjusting cutting heights may therefore represent a practical strategy to mitigate nitrate accumulation when alternative agronomic options are limited, contributing to more sustainable leafy vegetable production systems.