Kann man mit Nahinfrarot-Spektroskopie die Bodenfruchtbarkeit bestimmen?

Summary

Near-infrared reflectance spectroscopy is known for its inexpensiveness, rapidity and accuracy and may become a useful tool for the assessment of soil fertility. The objec-tives of this study were (i) to evaluate the ability of near-infrared reflectance spectros-copy (NIRS) to predict several soil chemical and biological characteristics of organi-cally managed arable land and (ii) to test if different sample pre-treatments yield comparable results. Spectra of the VIS-NIR region (400-2500 nm) from 56 either fresh or pre-treated (quick-freezing, freeze-drying and grinding) soil samples were recorded. A modified partial least square regression method and cross-validation were used to develop an equation over the whole spectrum (1st to 3rd derivation). Soil chemical and biological characteristics and ratios of them were predicted. The soil chemical charac-teristics pH (CaCl2) and contents of Corg, Nt and extractable P (Olsen), K (CAL) and Mg (CaCl2) were generally predicted well, except for the K content, which was predicted satisfactorily. The predictions were better for pre-treated samples than for fresh ones. The RSC (the ratio of standard deviation of laboratory results to standard error of cross-validation) ranged between 2.5 (pH) and 4.1 (Mg) and the correlation coefficient r between 0.91 (Mg) and 0.97 (Nt), respectively. NIRS-predictions of biological charac-teristics were for fresh samples slightly better than for pre-treated. Exceptions were content of ergosterol and the ratio of ergosterol content to Cmic. Respiration rate and contents of Cmic, Nmic and Pmic were predicted well. The RSC was between 2.5 (Pmic) and 4.6 (ergosterol) and r between 0.89 (respiration rate) and 0.93 (Cmic). Ratios of Cmic/Nmic and ergosterol/Cmic and the metabolic quotient were predicted satisfactorily. Nitrogen mineralization rate could not be predicted satisfactorily. The good and satis-factory results for soil chemical and biological characteristics indicate that there is marked potential of NIRS for soil fertility assessment. Quick-freezing and subsequent freeze-drying of samples is a promising method to maintain stability of biological sample characteristics.