| Description: |
Balsam fir trees are a specialty agricultural species that are largely used as Christmas trees. Soil or tissue sampling is seldom performed to assess balsam fir nutrition needs, which can contribute to over- or under-fertilization and subsequent environmental challenges. Remote sensing with vegetative indices has had strong relationships with nutrition in other plants. This research aimed to determine whether there is a relationship between normalized difference vegetation index (NDVI) and enhanced vegetation index 2 (EVI2) and nutrition in balsam fir. A random sample of 45 trees was selected in autumn of 2021 and then another 70 trees selected in spring of 2022. Soil and needle tissue samples were analyzed for N, P, K, Ca, Mg, S, Fe, Zn, Mn, B, and Cu. An uncrewed aerial vehicle equipped with a multispectral camera was flown over the orchard to determine the NDVI/EVI2 for each tree. Data were analyzed for correlations through all sampled trees. Separate correlation analyses were performed for mature trees (greater than 5 years old) and young trees (less than 5 years old). Soil nutrients N, P, and K had a significant relationship with NDVI in autumn sampling. Only tissue N was correlated consistently with NDVI in both autumn and spring, with R 2 of 37% and 33%, respectively. Relationships were much stronger when only mature trees were considered, increasing to 60% and 51%, respectively. Tissue N was correlated consistently with EVI in both autumn and spring, with R 2 of 58% and 40%, respectively, but had no improvement in mature trees. Ultimately both NDVI and EVI2 had predictive power for tissue N that can be useful to producers to help optimize fertilizer input. However, further work is needed to refine these relationships. |