Nutrient Stress Discrimination of N, P, and K Deficiencies in Barley Utilising Multi-band Reflection at Sub-leaf Scale

摘要

Discrimination of nutrient stress condition is the essential step prior to estimating the actual nutrient status using remote sensing. This research introduces a new methodology able to discriminate amongst non-stressed (C) barley plants and N, P, and K deficiency symptoms spectrally using just three narrow reflection bands utilising both the spectral and spatial dimension simultaneously. Nine spectral measurements were carried out on each plant using directed sampling technique. The measuring regions were spatially located at the tip, middle and base of the three last fully developed leaves. This design generated a four-dimensional data set consisting of the specific plant, the spectral dimension, the plant leaf position, and the position at the leaf. The barley plants were grown under controlled conditions, certifying the establishment of the three target deficiency symptoms (N, P and K and the non-stressed control). Three measurement occasions were carried out at three early growth stages within a time window of two weeks. Based on the results from the four dimensional multiway partial least square regression models (N-PLS) using the full spectral range (450-1000nm) for discrimination three central wavelengths were identified as essential in the discrimination model using the spatial inter leaf and intra leaf distribution. The stepwise N -PLS analysis with dummy response variables were able to correctly classify the four nutrient conditions with 94% success rate regardless of the respective growth stages within a time window of two weeks, using just three 2 nm wide wavebands: R450 (predominant pigment absorption region), R700 (the maximum chlorophyll response) and R810 (plant cell structural response region).