The Use of Nondestructive Sensors to Assess Nitrogen Needs of Greenhouse Plants

Floriculture growers are looking for new methods and technologies to help them improve crop productivity, enhance competitiveness, and increase sustainability.  Implementing precise site-specific management techniques on greenhouse crops allows growers to cut on the costs of nitrogen fertilizer, assure a higher quality product, and simultaneously be more eco-friendly. GreenSeeker^TM technology, introduced a new nondestructive pocket-sized sensor to generate Normalized Difference Vegetative Index (NDVI) values that use active optical sensors to measure greenness reflectance from plant leaves. The values are a good indirect indicator of the chlorophyll content and nitrogen status of the plant. To test the NDVI sensors effectiveness on two cultivars of marigold, zinnia, geranium, and begonia, five different nitrogen treatments (0, 5, 10, 15, and 20 g) of a 15N-9P-12K controlled release fertilizer, ranging from deficient to excessive, were applied to 32 pots per treatment.  After week two, 12 pots of the treatments with the lowest treatments and readings (0 and 5 g) were supplemented with extra fertilizer for recovery. All pots were completely randomized. Collected NDVI values showed different trends among species and cultivars within fertilizer treatments. Results also showed a weak correlation between sensor readings and leaf nitrogen concentration in the first two weeks of sensing due to interfering noise reflected from the media surrounding the small plants. As plants grew bigger, the correlation was more significant indicating that the sensor is a valid tool for assessing leaf nitrogen concentration in the vegetative stage before flowering and after filling out the pot. However, the recovery phase results showed only a marginal improvement in plant quality and salability at marketing time, but improved in quality two weeks later indicating that additional fertilizer may need to be added earlier in the production or in greater quantity at later dates.