Abstract
The objective of this study was to determine the relationships between nitrogen (N), phosphorus (P), potassium (P), acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents of sainfoin (Onobrychis sativa Lam.) pasture and canopy reflectance. Canopy reflectance measurements were made by using a portable spectroradiometer. An experiment was conducted in the Turkey in May and June in 2007 and 2008. Sainfoin pasture N, P, K, ADF and NDF contents correlated linearly with the reflectance ratios R780/650 (0.61≤ r2 ≤0.80) and first derivatives of the reflectance ratios 760/630 (0.70≤ r2 ≤0.84). Linear equations between each forage variable and reflectance or first derivatives reflectance had high r2 (0.68≤ r2 ≤0.83 and 0.79≤ r2 ≤0.90, respectively) in R780 and R760 wavelengths. In stepwise regression of the reflectance (in 460, 550, 650 and 780 nm wavelengths), the r2 of predicted and measured N, P, K, ADF and NDF contents of sainfoin pasture were (0.85, 0.85, 0.78, 0.81 and 0.74, respectively), in stepwise regression of the first derivatives of reflectance (in 440, 530, 630 and 760 nm wavelengths), the r2 of predicted and measured N, P, K, ADF and NDF contents of sainfoin pasture were (0.87, 0.91, 0.83, 0.93 and 0.86, respectively). Our results suggest that canopy reflectance in blue, green, red and near infrared wavebands with NIR/Red and NDVI ratios can be used for nondestructive prediction of forage quality variables in sainfoin pasture.
Highlights
Remote sensing techniques, based on measuring the reflected radiation from plant canopies, have the potential of evaluating the nutrient contents of many plants within the field of view of the sensor [1].Multispectral reflectance measured with hand-held radiometers has been used to estimate many plant parameters of interest [2]
These results indicate that correlations of standing pasture canopy reflectance in single broad wavebands with measured forage quality variables of sainfoin are high (Figure 1)
Forage quality variables closely correlated with canopy reflectance of near infrared waveband (780 nm)
Summary
Remote sensing techniques, based on measuring the reflected radiation from plant canopies, have the potential of evaluating the nutrient contents of many plants within the field of view of the sensor [1].Multispectral reflectance measured with hand-held radiometers has been used to estimate many plant parameters of interest [2]. Remote sensing techniques, based on measuring the reflected radiation from plant canopies, have the potential of evaluating the nutrient contents of many plants within the field of view of the sensor [1]. Researchers have evaluated remote sensing techniques for estimating the nutrient contents of growing crops by determining the appropriate wavelength or combination of wavelengths to characterize crop nutrient deficiencies [3]. In the visible spectrum (400-700 nm), leaf reflectance is low because of absorption by photosynthetic pigments (mainly chlorophylls and carotenoids). A relationship between spectral reflectance, visible absorption and macronutrients such as phosphorous, potassium, magnesium and calcium is expected due to their effect on the photosynthetic process in plants [5, 6]. Phosphorous is fundamental to tissue composition as well as being one of the components of the nucleic acids and enzymes
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