Optical Sensors for Optimizing Nitrogen Application in Broccoli Seedlings Production

Effective nitrogen (N) fertilization management is a key aspect in the nursery production of vegetable crops. The application of precision agriculture techniques and technologies can play a relevant role in the sustainable management of N crop nutrition. Proximal sensing represents a resource for rapid and non-destructive plant monitoring. In this work, the reliability of portable photonics-based devices in discriminating different levels of N treatment was evaluated on broccoli seedlings. Broccoli seedlings (Brassica oleracea L. var. italica cv. Naxos F1) were grown in a Mediterranean greenhouse, using nutrient solution with 5 different N concentrations (0, 4.5, 9, 15, 22.5 mM), with 4 replicates per treatment. Optical data and laboratory measurements were collected at the commercial seedling stage. Several optical and biometric measures were acquired using portable sensors, i.e., fluorescence indices using Dualex and Multiplex, the Normalized Difference Vegetation Index using GreenSeeker and the Green Canopy Cover and Leaf Area Index (LAI) using Canopeo and PocketLAI mobile apps, respectively. In our experimental conditions, a Multiplex index related to epidermal flavonoids (FLAV) was promising in predicting total Kjeldahl N tissue concentration, accordingly to the trend observed among treatments, while LAI index was able to predict biomass trend. Based on these results, the monitoring of broccoli seedling growth by proximal sensors could be included in the development of a sustainable strategy for greenhouse horticulture.