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Open AccessFeature PaperArticle

Application of Proximal Optical Sensors to Fine-Tune Nitrogen Fertilization: Opportunities for Woody Ornamentals

1
Department Plants and Crops, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium
2
Department of Biosystems, Faculty of Bioscience Engineering, KU Leuven, Kasteelpark Arenberg 20, 3001 Leuven, Belgium
3
Soil Service of Belgium, Willem de Croylaan 48, 3001 Leuven, Belgium
4
PCS Ornamental Plant Research, Schaessestraat 18, 9070 Destelbergen, Belgium
*
Author to whom correspondence should be addressed.
Agronomy 2019, 9(7), 408; https://doi.org/10.3390/agronomy9070408
Received: 17 June 2019 / Revised: 5 July 2019 / Accepted: 16 July 2019 / Published: 23 July 2019
Today, high amounts of residual nitrogen are regularly being reported in the open field production of hardy nursery stock. In some cases, excessive fertilizers or side-dressings are applied when circumstances are not favorable for uptake. Aquatic as well as terrestrial ecosystems are sensitive to enrichment with nutrients, but growers also benefit when losses are avoided. In this study, the potential of proximal optical sensors to optimize nitrogen fertilization was investigated in four woody species: Acer pseudoplatanus L., Ligustrum ovalifolium Hassk., Prunus laurocerasus ‘Rotundifolia’ L. and Tilia cordata Mill. For three consecutive growing seasons, plants were grown under three different fertilization levels to generate different nitrogen contents. Plant growth and nitrogen uptake were monitored regularly and combined with sensor measurements including Soil Plant Analysis Development (SPAD), Dualex and GreenSeeker. Here, we show that optical sensors at the leaf level have good potential for assisting growers in the sustainable management of their nursery fields, especially if leaf mass per area is included. Nevertheless, care should be taken when plants with different leaf characteristics (e.g., wax-layer, color, and leaf thickness) are measured. When all measuring years were considered, high correlations (R2 ≥ 0.80) were found between area-based foliar nitrogen content and its non-destructive proxy (i.e., chlorophyll)measured by Dualex or SPAD. Based on our results, we recommend a relative rather than absolute approach at the nursery level, as the number of species and cultivars produced is very diverse. Hence, knowledge of absolute threshold values is scarce. In this relative approach, a saturation index was calculated based on the sensor measurements of plants grown in a reference plot with an ample nitrogen supply. View Full-Text
Keywords: nursery management; SPAD; Dualex; GreenSeeker; Acer pseudoplatanus; Ligustrum ovalifolium; Prunus laurocerasus; Tilia cordata nursery management; SPAD; Dualex; GreenSeeker; Acer pseudoplatanus; Ligustrum ovalifolium; Prunus laurocerasus; Tilia cordata
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MDPI and ACS Style

Bracke, J.; Elsen, A.; Adriaenssens, S.; Schoeters, L.; Vandendriessche, H.; Van Labeke, M.-C. Application of Proximal Optical Sensors to Fine-Tune Nitrogen Fertilization: Opportunities for Woody Ornamentals. Agronomy 2019, 9, 408.

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