SOM and Biomass C Stocks in Degraded and Undisturbed Andean and Coastal Nothofagus Forests of Southwestern South America

Abstract

Abstract:Grazing and over-exploitation can severely degrade soil in native forests. Considering that productivity in ecosystems is related to soil organic matter (SOM) content and quality, the objectives of this study were to: (1) determine the influence of degraded (DEF), partly-degraded (PDF), and undisturbed (UNF) Nothofagus forests on the stocks of carbon (C) in tree biomass and SOM; (2) evaluate fractions of SOM as indicators of sustainable management; and (3) use the Century model to determine the potential gains of soil organic C (SOC). The forests are located in the Andes and Coastal mountains of southern Chile. The SOM was fractionated to separate the light fraction (LF), macroaggregates (>212 µm), mesoaggregates (212-53 µm), and microaggregates (<53 µm). In two measurement periods, the SOC stocks at 0-20 cm and 20-40 cm depths in macroaggregates were on average 100% higher in the Andean UNF, and SOC was over twice as much at 20-40 cm depth in Andean DEF. Century simulations showed that improved silvopastoral management would gradually increase total SOC in degraded soils of both sites, especially the Ultisol with a 15% increase between 2016 and 2216 (vs. 7% in the Andisol). Greater SOC in macroaggregates (p < 0.05) of UNF indicate a condition of higher sustainability and better management over the years.

Potential Model Overfitting in Predicting Soil Carbon Content by Visible and Near-Infrared Spectroscopy

“…For Ultisol, the lower values of TC were clearly observed in the depth of 20-40 cm. However, outliers were found for values greater than 4%, probably due to such samples being taken from undisturbed Nothofagus forest conditions [27]. The minimum and maximum frequency of the TC values were 1 and 14 ( Figure 2B), respectively.…”

“…However, the correlation coefficient between spectral bands and TC in the region of 500-700 nm (r ≈ −0.5), were poorer than those reported by others [19,34] (r = −0.8 or better). One possible explanation of this is the spectral distortion due to natural source of light used for scanning the samples (outdoor scanning) and low bulk density of the studied soils (≤ 1 g· cm −3 ) [27] which promote more dispersion of light [45]. This distortion was probably not successfully corrected by the Savitzky-Golay filter.…”

“…The study took place in the Biobio and Araucanía Regions of Chile ( Figure 1). Two soil orders were selected for the experiment: (1) Andisol, located in the Andean range (medial, amorphic, mesic, Typic Hapludands) [23]; and (2) Ultisol, which is located in the coastal range (very fine, mixed, semiactive, mesic Typic Paleudults) [27]. In both experimental sites the land cover is dominated by Nothofagus obliqua and Nothofagus nervosa.…”

“…A total of 70 samples were taken from the sites and three soil layers were sampled at depths of 0-5, 5-20, and 20-40 cm. The sampling strategy was selected to represent different conditions of the native forest, from undisturbed to degraded ( Figure 1, for details see [27]). The samples were kept in plastic bags and stored at −4 • C for later analysis.…”

Growth and nutrient balance of Asystasia gangetica (L.) T. Anderson as cover crop for mature oil palm (Elaeis guineensis Jacq.) plantations

“…Availability of N, P, and K after treatment (recovery nutrient) was higher in soils with N. biserrata and A. gangetica than without cover crops (Table 2). Dube and Stolpe (2016) and Alfaro et al (2018) reported that soil nutrient availability was higher in soil covered by cover crops than without cover crops. According to Alfaro et al (2018), availability of soil nutrients is related to cover crops.…”