Modelling plant growth and nitrogen uptake for optimal nitrogen fertilization of rocket (Diplotaxis tenuifolia L.)

Rocket is very sensitive to nitrogen fertilization and an incorrect management of this nutrient can easily limit growers’ incomings since defects or excesses are both detrimental for the achievement of high yield and quality. Low nitrogen availability in the root zone, below a certain threshold, significantly decreases plant biomass. On the other hand, this species easily accumulates excess nitrate in the edible organs, which is harmful for human health, and may become an issue for marketing. Piana del Sele, in the Campania Region (South Italy), is the most important production area for rocket in Italy. In this area, this species is cultivated intensively under protected cultivation. In greenhouse, crop nitrogen uptake is one of the most important variables driving fertilizer distribution if a correct irrigation management is applied to prevent nitrogen leaching. Therefore, in this work we calibrated and validated a photosynthesis-based model to simulate plant growth and eventually nitrogen uptake as a function of the daily accumulated plant dry biomass and optimal nitrogen concentration in plant tissues. Experimental data were collected on rocket (Diplotaxis tenuifolia) grown in containers for the determination of optimal nitrogen concentration in plant tissues, and under operational condition, in a commercial greenhouse, for the validation of the model. Plants were sown in October-November 2021 and consecutive harvestings (cuttings) were considered for model calibration and validation. At each cutting, plant biomass was collected in triplicates and nitric and total nitrogen analyzed in the edible organs. Air temperature and radiation, used as main model driving variables, and other environmental parameters (i.e., soil and air humidity), were monitored. The linear analysis of simulated versus measured data showed a high capability of the model to predict plant growth and nutrient requirements.