Determination of nitrogen and ash contents in total herbage and botanical components of grassland systems with near infra‐red spectroscopy

Abstract

: Near infra-red reýectance spectroscopy (NIRS) was used to develop calibration equations to measure nitrogen and ash contents in grassland samples. Four populations of samples were collected or prepared : total herbage, with a heterogeneous and complex botanical composition, and its botanical components (grasses, legumes and forbs). A set of samples from each population was selected to develop the speciüc calibration equations using three mathematical data treatments (log 1/R, ürst and second derivative). Six and seven wavelengths were selected by multiple regression to predict nitrogen and ash contents, respectively. Calibration equations were evaluated by comparing the values obtained by reference methods (Kjeldahl test and dry ashing measurements) with those predicted by NIRS. The three data treatments generally provided similar results as regards estimations of nitrogen contents. The correlation coefficients varied from 0.94 to 0.98, and the standard errors of prediction ranged from 1.10 to 1.49 g kg-1 (total herbage), from 0.73 to 0.98 g kg-1 (grasses), from 0.99 to 1.30 g kg-1 (legumes) and from 0.76 to 0.80 g kg-1 (forbs). The most suitable treatments to predict ash contents were log 1/R and the ürst derivative. The best performance was obtained for legumes, using log 1/R, with a correlation coefficient of 0.95 and a standard error of prediction of 3.54 g kg-1. The calibration equations became more accurate as the components of the sets of samples became botanically simpler. Prediction accuracy was greater when the speciüc calibration equations for each population of samples were used.

NIRS prediction of the feed value of temperate forages: efficacy of four calibration strategies

“…In our study, R 2 CV ranged from 0.77 to 0.94 and SEP ranged from 4.9 to 20.0 g/kg DM. Ruano-Ramos et al (1999) report results similar to those found for lucerne, red clover, timothy and permanent grasslands, whereas the SEP obtained by Windham et al (1991) came closest to the SEP obtained for Italian rye-grass samples. These authors highlight the importance of soil contamination in the SEP obtained, particularly when equations were generated with first or second derivatives of log 1/R.…”

“…In theory, inorganic substances do not have near-infrared absorption bands. However, successful CA measurements by NIRS have been reported for grasses and lucerne by Clark et al (1987) and for pastures by Windham et al (1991) and Ruano-Ramos et al (1999). The perfect correlation between CA and organic matter content could explain these good results.…”

“…SEP associated with the broad-based equations developed for total legumes were lower than the SEP of the calibration models developed for total grasses. According to Ruano- Ramos et al (1999), the simpler botanical composition of legumes (only samples of lucerne and red clover) relative to grasses (five species plus permanent grasslands) could explain these results. However, cross-comparison of the weighted SEP using FAMILY predictions (10.66) and the SEP obtained for the global calibration (9.89) was unable to find differences.…”

Potential of imaging spectroscopy as tool for pasture management

“…Near-infrared spectroscopy is based on diffuse reflectance of dried and ground samples and this technique is widely used for constituent assessment of crops in the laboratory (e.g. Berardo, 1997;Ruano-Ramos et al, 1999). Some successful efforts have been made to relate diffuse reflectance of undried material to constituent composition (e.g.…”

The Effect of the Invasive Plant Species Lupinus polyphyllus Lindl. on Energy Recovery Parameters of Semi-Natural Grassland Biomass

“…Compared to other research results from semi-natural grassland biomass [9,10,18,19], the mineral concentration values for the L0 biomass are within the expected range for biomass harvested in June; however, the values for the L100 samples for Ca, Mg and N were considerably higher. This corresponds with previous findings, which likewise found higher mineral content, particularly for Ca, Mg and N [20,21], in legumes and other dicotyledonous plants compared to grasses. However, the observed values for mineral composition, especially for N, K, Mg, S and Cl, led to the conclusion that a direct combustion of the material, be it lupine, semi-natural grassland biomass, or any mixture of the two, as press fluid and press cake originating from grassland biomass with lupine content between 0 (L0) and 100% FM (L100).…”