Use of nondestructive sensors to assess nitrogen status in potted poinsettia (Euphorbia pulcherrima L. (Willd. ex Klotzsch)) production

• We evaluated the response of two cultivars of poinsettia to five controlled release fertilizer rates.
• We compared different optical sensors to actual leaf nitrogen.
• We corrected deficient treatments with extra fertilizer to improve production.
• SPAD and atLEAF were more correlated to leaf nitrogen than NDVI.
• Treatment correction showed improvement in the 5 (+5 g) treatment.

Utilizing precision farming techniques in a greenhouse setting to manage plant site-specific nitrogen (N) needs can help to prevent N deficiency, increase final plant quality, reduce cost of excessive fertilizer, and prevent N runoff. Optical sensors are a fast and nondestructive approach to estimate plant chlorophyll content by measuring the reflectance or absorbance of the green leaves. The objective of this study was to test the reliability of normalized difference vegetative index (NDVI) values calculated by the GreenSeeker™ hand held sensor as an indirect indicator of poinsettia (Euphorbia pulcherrima L. (Willd. ex Klotzsch) N status, and compare the sensors performance to other optical sensors on the market. The second objective of the study was to investigate if plant quality is improved by correcting N fertilizer application during production based on the sensor readings. The experiment was conducted in fall 2013. Poinsettia ‘Prestige Red’ and ‘Freedom Red’ pots were supplemented with 0, 5, 10, 15, and 20 g of 15N-9P-12K controlled release fertilizer (CRF). Soil and plant analysis development (SPAD) chlorophyll meter, GreenSeeker™ NDVI sensor, and atLEAF meter readings were recorded for four consecutive weeks. Readings and visual qualities differences were monitored for significant separation between the different rates. At 40 days after planting (DAP), based on visual qualities differences, half of the deficient treatments were supplemented with extra fertilizer for treatment correction. All pots were completely randomized. All sensors values were compared to actual leaf N concentration to determine efficiency. Plants were assessed at the end of commercial production period by recording final height, final width, number of bracts, length of bract, dry weight, and salability. The GreenSeeker™ NDVI sensor correlated well with actual leaf N concentration during the vegetative phase of poinsettia production. As for the overall production period, SPAD and atLEAF meters showed an advantage with greater correlation to actual leaf N concentration. The GreenSeeker™ readings were less correlated with leaf N concentration at early stages of establishment due to plants small size and background noise, as well as at later stages of establishment due to anthesis. Poinsettia ‘Freedom Red’ responded better to treatment correction than ‘Prestige Red’. The correction treatments showed greater results for plant growth in the treatment correction 5 (+5 g) compared to treatment correction 0 (+10 g), and as good as the 10 g treatment, indicating that the correction treatment could be used to correct deficiencies during production.