Determining Variability within Leaf Analysis and Reflectance Sensor Sampling Methods

Leaf nitrogen concentration (LNC) has been correlated with Soil Analysis Plant Development (SPAD) and atLEAF chlorophyll reflectance sensors in greenhouse grown potted floriculture crops.  However, it is unclear if leaf sensor location and sampling procedure for (LNC) affects data values and correlations. Plugs (2 to 4 leaves) of ornamental kale (Brassica oleracea L.) cultivar Tokyo Red were transplanted into standard 15.2 cm diameter pots with about 0.35 kg 902 Metro-Mix media.  Fertilizer treatments of 0, 5, 10, or 15 g of 16-9-12 N-P-K Osmocote® Plus were applied as a topdress application, and tap water was then used during irrigations.  Pots were arranged in a completely randomized design.  Individual plants were scanned from the same 10 pots per treatment for SPAD and atLEAF every week for five weeks starting 30 d after planting.  For each pot, SPAD and atLEAF measurements were taken from a single mature leaf from the middle to upper level of the plant either at the leaf tip (T), from the middle of the leaf not including the midrib (M), or towards the bottom of the leaf not including the midrib (B).  Leaf foliar analysis consisted of collecting either all fully developed leaves from a single plant (SP), three fully developed leaves from five different plants per treatment and bulked (FP), three fully developed leaves from 10 different plants per treatment and bulked (TP), using only the tip portion (top ~1.5 cm) of three fully developed leaves from 10 different plants per treatments (TIP), using only the middle portion (middle ~2.0 to 2.5 cm) of three fully developed leaves from 10 different plants per treatments (MID),  or using only the bottom portion (bottom ~2.0 cm) of three fully developed leaves from 10 different plants per treatments without petioles (BOT) for total leaf nitrogen concentration per sampling treatment weekly.  A significant position affect was seen in both SPAD and atLEAF sensors.  For SPAD, (F) and (M) of a leaf were not significantly different from each other, but were significantly different from (B).  All three positions for atLEAF were significantly different from each other.  A significant difference was seen among leaf sampling methods for (LNC).  Treatments (SP), (FP), (TP), and (BOT) were not significantly different from each other, but were significantly different than (T) and (M).  Significant correlations were seen among all combinations of sensor positions and leaf nitrogen sampling methods except (SP) and SPAD (T) where p=0.055.