| This work describes the constraints and opportunities of performing an estimation of soil
organic carbon (SOC) in a field scale, using a visible and near infrared (VisNIR) spectral
SOC model developed for a relatively large post-glacial geographical mezoregion. The
Poznan Lakeland (bounding box: 52o05’N, 15o30’E; 52o45’N, 16o58’E), which is the
region of interest, covers the area of over 3100 km2 and its soil cover comprises of
a number of various soil types, such as: Haplic Luvisols, Albic Luvisols, Haplic
Albeluvisols Haplic Phaeozems, Gleyic Chernozems, Brunic Arenosols and Mollic
Gleysols. The soils of the region developed from different parent materials and several
geomorphological landscapes are present in the region, including: undulating ground
moraines, sandur fields, marginal aggradation plains, subglacial troughs and kame
terraces.
The initial regional dataset of 72 samples was built to reflect the soil diversity of the
region. The soil samples were air dried, ground, and sieved through 2mm sieve.
SOC content was measured in the collected samples by the dichromate oxidation
(Walkey Black’s) method. The VisNIR reflectance measurements were taken in the
laboratory conditions using ASD Fieldspec 3 spectrometer. The diversity of soil
forming factors made it difficult to develop a well performing VNIR model that would
explicitly explain the diversity of all soil types within the analyzed region. Therefore
several sub-models were proposed. The sub-sets of soil samples were delimited
according to a given soil type, soil texture or inherent spectral properties revealed
by the clustering of soil spectra, which is discussed in detail in the corresponding
study.
Two study sites were selected within the boundaries of the Poznan Lakeland region to test
the regional SOC modeling and perform field-scale predictions of SOC. Both sites were
located within the undulating ground moraines landscape, but the areas comprised
of different soil cover. The predominant soil types of Chlewiska site (centroid:
52o30’48”N, 16o38’27”) are Gleyic Chernozems and Albic Luvisols, developed from the
clayey parent material. On the other hand, Brunic Arenosols and Haplic Luvisols
occurring in the Sobota site (centroid: 52o31’23”N, 16o49’01”), developed from
sands.
The SOC estimation results obtained for both local datasets (Chlewiska: 68 samples;
Sobota: 90 samples) were compared with the cross-validation of the SOC local models
and the decline of the results was assessed and then compared between the two
analyzed sites. Additionally, the spatial distributions of SOC content measured using
the reference method was obtained using kriging interpolation. Finally, they were
confronted with the spatial distributions predicted either by a local or a regional model. |