Use of an Active Canopy Sensor and SPAD Chlorophyll Meter to Quantify Geranium Nitrogen Status

Abstract

<jats:p>This research was conducted to investigate the potentials of normalized difference vegetation index (NDVI), a Soil-Plant Analyses Development (SPAD) chlorophyll meter, and leaf nitrogen (N) concentration [% dry matter (DM)] for rapid determination of N status in potted geraniums (<jats:italic>Pelargonium ×hortorum</jats:italic>). Two F<jats:sub>1</jats:sub> cultivars were chosen to represent a dark-green leaf cultivar, Horizon Deep Red, and a light-green leaf cultivar, Horizon Tangerine, and were grown in a soilless culture system. All standard 6-inch (15.24-cm) pots filled with a medium received an initial top-dress application of 5 g controlled-release fertilizer (15N–9P–12K), then plants were supplemented with additional N in the form of urea at 0, 50, 100, or 200 mg·L<jats:sup>−1</jats:sup> N every few days to produce plants ranging from N-deficient to N-sufficient. The NDVI readings of individual plants from a NDVI pocket sensor developed by Oklahoma State University were collected weekly until the flowering stage. Data on flower traits, including number of pedicels (NOP), number of full umbels per pot (NOFU), total number of flowers per pot (TNF), number of flowers per pedicel (NOF), and inflorescences diameter (IFD), were collected 3 months after initial fertilizer treatment. After measuring flower traits, pedicels were removed from each pot, and SPAD value, NDVI, and leaf N concentration (g·kg<jats:sup>−1</jats:sup> DM) were measured simultaneously. Cultivar and N rate significantly affected all but two flower and one N status parameters studied. The coefficient of determination <jats:italic>R</jats:italic><jats:sup>2</jats:sup> showed that NOP, NOFU, and TNF traits were more related to the N rates and the status parameters studied for ‘Horizon Tangerine’ than for ‘Horizon Deep Red’. For the latter cultivar, NOP and TNF traits were highly related to NDVI and SPAD values than N rates and leaf N content parameters. Correlation analysis indicated that the NDVI readings (<jats:italic>R</jats:italic><jats:sup>2</jats:sup> = 0.848 and 0.917) and SPAD values (<jats:italic>R</jats:italic><jats:sup>2</jats:sup> = 0.861 and 0.950) were significantly related to leaf N content (g·kg<jats:sup>−1</jats:sup> DM) between cultivars. However, sensitivity of the NDVI and chlorophyll values to N application rate in geranium was slightly less than leaf N content. Strong correlations (<jats:italic>R</jats:italic><jats:sup>2</jats:sup> = 0.974 and 0.979, respectively) between NDVI and SPAD values were found within cultivars. The results demonstrated NDVI and SPAD values can be used to estimate N status in geranium. Because the pocket NDVI sensor will be cheaper than the SPAD unit, it has an advantage in determining N content in potted ornamentals.</jats:p>

Effect of Cultivar on Chlorophyll Meter and Canopy Reflectance Measurements in Cucumber

“…Cultivar differences in NDVI were reported by Sultana et al [17] who observed significant differences in NDVI between wheat cultivars under four different nitrogen levels. Similar results for geranium (Pelargonium × hortorum) were reported by Wang et al [48]. The lack of consistent differences in the N1 treatment, in the present work, may be due to the limited vegetative growth of this treatment, the lack of continuity of vegetative cover may have influenced canopy reflectance.…”

“…Padilla et al [28] reported that these vegetation indices were good estimators of crop N status in cucumber. Previous studies in tomato and geranium have reported strong relationship between vegetation indices such as NDVI and GNDVI with leaf N content [25,48].…”

“…The lack of consistent differences in the N1 treatment, in the present work, may be due to the limited vegetative growth of this treatment, the lack of continuity of vegetative cover may have influenced canopy reflectance. Padilla et al [5], Wang et al [48] and Johansen and Tømmervik [49], reported that NDVI is susceptible to measurement error caused by background reflectance when the canopy is not sufficiently closed. Comparing the LAI between the different cultivars, 'Strategos' had the highest LAI values, but this did not influence vegetation indices; the values of vegetation indices were generally comparable, in statistical terms, between cultivars.…”

Assessing Performance of Vegetation Indices to Estimate Nitrogen Nutrition Index in Pepper

“…In the vegetative stage, the plants are small and have low foliage density, which could affect reflectance measurements by the inclusion of background noise [11,15]. Johansen and Tømmervik [57] and Wang et al [58] reported a lack of precision with NDVI until the plant canopy achieved adequate coverage. In the harvest stage, mottling and discoloration of older leaves, because of crop age, can affect reflectance measurements, as has been reported for cucumber [46].…”

Use of Nondestructive Sensors to Assess Nitrogen Status in Potted Dianthus (Dianthus chinensis L.) Production

“…For greenhouse crops, NDVI has proven to correlate well with leaf N concentration for geranium (Pelargonium ×hortorum L.H. Bailey) (Wang et al 2012a(Wang et al , 2012b and cabbage (Brassica oleracea L.) (Dunn and Goad 2015). No previous research has been conducted on the use of the GreenSeeker™ NDVI sensor to assess N status in dianthus.…”