Non-destructive monitoring and diagnosis of plant nitrogen (N) concentration status is necessary for precision in N management. Leaf -N and chlorophyll (Chl) concentration of fodder crops are important indicators of plant N status. Studies were conducted to determine the relationship between canopy hyperspectral reflectance (325 to 1075 nm) and Chl or N concentration in field grown fodder crops [bajra (Pennisetum typhoides, sorghum (Sorghum bicolor L.) in Kharif season and oat (Avena sativa) in Rabi season] without and with recommended dose of nitrogen of different crops. Nitrogen fertilizer application mainly affected leaf reflectance at 575 and 623 nm in sorghum, 565 and 657 nm in bajra and 563 and 716 nm in oat. The reflectance ratio at R₅₈₁/R₃₉₇ (R²=0.46**) and R₆₁₉/R₄₆₂ nm (R²=0.79***) had the highest correlation with sorghum and bajra leaf N concentration respectively with greatest R² values. However in oat single reflectance at R₅₄₂ (R²=0.53**) had the highest correlation with leaf N concentration. Similarly, sorghum, bajra and oat leaf Chl concentration were highly correlated with R₆₇₇/R₅₂₇ (R²=0.63**), R₆₈₈/R₄₀₉ (R²=0.71***) and R₆₉₅ (R²=0.56** ), respectively. A linear relationship was found between sorghum leaf N and a simple ratio at R₅₈₁/R₃₉₇ (Intercept=8.85, slope=-2.64, R²=0.44). Bajra leaf N concentration was associated closely with ratio of R₆₁₉/ R₄₆₂, (R²= 0.78***). Oat leaf N concentration could be best estimate through single reflectance at R₆₉₅ (Slope=-0.48, Intercept=0.15; R²=0.56). Similarly sorghum, bajra and oat leaf Chl could be best-estimated using reflectance ratio of R₆₇₇/R₅₂₇, R₆₁₅/R₄₁₁ and R₆₉₅, respectively. Thus our results suggest that spectral reflectance measurements hold promise for the assessment of some physiological parameter at the leaf level real time monitoring of sorghum and bajra N status and N fertilizer management.

Date Published: 20 April 2010
PDF: 16 pages
Proc. SPIE 7676, Sensing for Agriculture and Food Quality and Safety II, 76760P (20 April 2010); doi: 10.1117/12.852312

Published in SPIE Proceedings Vol. 7676:
Sensing for Agriculture and Food Quality and Safety II
Moon S. Kim; Shu-I Tu; Kaunglin Chao, Editor(s)