Determination of Total Carbon and Nitrogen Content in a Range of Tropical Soils Using near Infrared Spectroscopy: Influence of Replication and Sample Grinding and Drying

Abstract

Near infrared (NIR) refl ectance spectroscopy has been receiving increased attention for the rapid and inexpensive determination of soil properties and of total carbon (Ct) and nitrogen content (Nt) in particular. However, methodological aspects such as sample grinding and drying or replication have not been addressed extensively. The objectives of the paper were, thus, to assess how NIR predictions of Ct and Nt were affected by sample grinding (2 mm sieving vs. 0.2 mm grinding), drying (air-drying vs oven-drying at 40°C during 24 h) and replication (use of one to six sub-samples to determine average spectra). This was performed on a range of tropical soils that differed widely in mineralogy (low and high activity clay soils, allophanic soils) and texture (sandy to clayey). The accuracy of the NIR predictions of Ct and Nt was higher with oven-dried compared to air-dried samples and, more markedly, with 0.2 mm ground compared to 2 mm sieved samples. Replication had a positive effect on NIR predictions when 2 mm sieved samples were used, especially for air-dried samples, but this effect was not clear with 0.2 mm ground samples. Thus, the most accurate predictions of Ct and Nt were obtained with oven-dried fi nely ground samples, with limited response to sample replication. Accurate predictions were, however, also obtained with four replicates on oven-dried 2 mm sieved samples. Acceptable and less tedious results could, thus, be achieved when replacing fi ne grinding by replication. Even with this procedure, the r² between predicted (NIR) and measured (reference) values was 0.9 and the ratio of standard error of prediction to mean (CV%) was 20% which can be considered satisfactory for the heterogeneous sample set under study.

Are NIR spectra useful for predicting site indices in sandy soils under Eucalyptus stands in Republic of Congo?

“…The calibration performances for organic carbon and total nitrogen obtained during this study (R 2 = 0.91 and 0.92 for carbon and nitrogen, respectively) were of the same order of magnitude as those obtained by Barthès et al (2006) with 0.94 and 0.92 for carbon and nitrogen, respectively and Brunet et al (2007) with 0.91 and 0.87 for carbon and nitrogen, respectively. These two studies were carried out on a large range of tropical sandy and clayey soils with similar sample treatments: 2 mm sieving, two repetitions on the same sample and using a first order derivative for regressions.…”

“…NIRS is a non-destructive physical analysis method that is used extensively to predict soil organic properties, particularly total carbon and total nitrogen (e.g., Dalal and Henry, 1986;Morra et al, 1991;He et al, 2005;Barthès et al, 2006;Brunet et al, 2007). Other properties linked to organic matter (OM) may also be predicted, such as the carbon and nitrogen concentrations in particle size fractions , cation exchange capacity (CEC), water content, metal content (e.g., Fe, Cu, Zn), or soil texture (Chang et al, 2001(Chang et al, , 2005Chang and Laird, 2002;Morón and Cozzolino, 2003;Vergnoux et al, 2010).…”

Visible and Near Infrared Spectroscopy in Soil Science

“…Fystro (2002) found a slightly increased prediction error for organic carbon and total nitrogen using air-dry, ball-milled (<0.5 mm) soil compared with coarse (<4 mm) soil, as did Russell (2003) for soil treated in a puck and ring grinder compared with soil crushed and sieved through 2 mm. Barthes et al (2006), on the other hand, reported a positive result of grinding (<0.2 mm) compared with sieving soil (<2 mm). They suggested that the contradictory results were due to different responses to grinding between aggregated clay soils and single-grain, coarse-textured soils, as crushing clay aggregates would produce more homogeneous samples.…”

Determination of local nitrogen loss for exploitation of sustainable precision agriculture: approach description

“…Each sample comprised 1.5 kg of soil collected from 6-7 sub-samples on a radius of 2.5 m from the reference position, at a standard 0.3 m depth. Total nitrogen (as a result of N available at the beginning of the cycle plus N mineralized from organic matter) was determined based on Near Infrared Spectroscopy (NIR) [10]. Data underwent a standard resampling weighted on a nearest-neighbor weighted function, in order to allow realization of a homogeneous map over the experimental field (Figures 1-1 and 1-2).…”