Use of Spectral Reflectance Values for Determining Nitrogen, Phosphorus, and Potassium Contents of Rangeland Pla nts

Abstract

This study was carried out to determine nitrogen, p hosphorus, and potassium contents of rangeland plants using spectral reflectance valu e. The measurements were made in 1 m 2 area of different parts of a rangeland. A portable spectroradiometer capable of measuring the wavelength range of 325-1,075 nm of t he electromagnetic spectrum was used to collect spectral data. Spectral measurement s were made in a rangeland while nitrogen, phosphorus, and potassium content of the plants were determined in a laboratory. Stepwise linear regression was used to select wavelengths to investigate relationships between laboratory analysis results a nd spectral data. According to the result, significant relationships existed between p redicted and measured nutrients, with R 2 values of 0.85, 0.43, and 0.84 for nitrogen, phosp horus and potassium, respectively. While 11 wavelengths (R 609 , R 647 , R 651 , R 654 , R 669 , R 675 , R 676 , R 680 , R 721 , R 727 , R 760 ) were used in the equation for estimating nitrogen level, 2 wa velengths (R 675, R 680 ) and fifteen wavelength (R 410, R 411, R 417, R 422, R 460, R 463, R 468, R 646, R 651, R 658, R 669, R 670, R 674, R 676, R 682 ) were determined for phosphorus and potassium levels , respectively. The results indicated that the changes in nitrogen, phosphorus, and potas sium content affected reflectance values of the visible region of spectrum (especiall y in the red regions) and, therefore, spectral reflectance data could be used to estimate the nitrogen, phosphorus and potassium contents in rangeland plants. Keywords: Plant nutrient elements, Rangeland, Remote sensing , Spectral reflectance.