Abstract
Nitrogen (N) has commonly been applied in Eucalyptus stands in Brazil and it has a direct relation with biomass production and chlorophyll content. Foliar N concentrations are used to diagnose soil and plant fertility levels and to develop N fertilizer application rates. Normally, foliar N is obtained using destructive methods, but indirect analyses using Vegetation Indexes (VIs) may be possible. The aim of this work was to evaluate VIs to estimate foliar N concentration in three Eucalyptus clones. Lower crown leaves of three clonal Eucalyptus plantations (25 months old) were classified into five color patterns using the Munsell Plant Tissue Color Chart. For each color, N concentration was determined by the Kjeldahl method and foliar reflectance was measured using a CI-710 Miniature Leaf Spectrometer. Foliar reflectance data were used to obtain the VIs and the VIs were used to estimate N concentrations. In the visible region, the relationship between N concentration and reflectance percentage was negative. The highest correlations between VIs and N concentrations were obtained by the Inflection Point Position (IPP, r = 0.97), Normalized Difference Red-Edge (reNDVI, r = 0.97) and Modified Red-Edge Normalized Difference Vegetation Index (mNDI, r = 0.97). Vegetation indexes on the red edge region provided the most accurate estimates of foliar N concentration. The reNDVI index provided the best N concentration estimates in leaves of different colors of Eucalyptus urophylla × grandis and Eucalyptus urophylla × urophylla (R2 = 0.97 and RMSE = 0.91 g kg−1).
Highlights
Nitrogen (N) is one of the essential elements required in many sites to optimize growth of Eucalyptus stands in Brazil (Santana et al, 2000)
Nitrogen (N) has commonly been applied in Eucalyptus stands in Brazil and it has a direct relation with biomass production and chlorophyll content
The highest correlations between Vegetation Indexes (VIs) and N concentrations were obtained by the Inflection Point Position (IPP, r = 0.97), Normalized Difference Red-Edge and Modified Red-Edge Normalized Difference Vegetation Index
Summary
Nitrogen (N) is one of the essential elements required in many sites to optimize growth of Eucalyptus stands in Brazil (Santana et al, 2000). Nitrogen is associated with several important proteins in the photosynthetic process (Moran et al, 2000; Ollinger, 2011). Foliar N analyses are commonly obtained using destructive sampling methods and little progress has been made in the development of indirect analyses based on spectral characteristics (Ollinger, 2011). In this context, the use of non-destructive analyses using the foliar reflectance spectrum to estimate the chlorophyll content has been improved (Gitelson et al, 2009; Sims and Gamon, 2002; Ustin et al, 2009). The reduction of chlorophyll content implies lower energy absorption in the visible spectrum (400 – 700 nm) and greater foliar reflectance in the electromagnetic spectrum (Richardson et al, 2002)
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