Variation of soil organic carbon, stable isotopes, and soil quality indicators across an erosion–deposition catena in a historical Spanish olive orchard

Abstract

Abstract. This study compares the distribution of bulk soil organic carbon (SOC), its fractions (unprotected and physically, chemically, and biochemically protected), available phosphorus (Pavail), organic nitrogen (Norg), and stable isotope (δ15N and δ13C) signatures at four soil depths (0–10, 10–20, 20–30, and 30–40 cm) between a nearby open forest reference area and a historical olive orchard (established in 1856) located in southern Spain. In addition, these soil properties, as well as water stable aggregates (Wsagg), were contrasted at eroding and deposition areas within the olive orchard, previously determined using 137Cs. SOC stock in the olive orchard (about 40 t C ha−1) was only 25 % of that in the forested area (about 160 t C ha−1) in the upper 40 cm of soil, and the reduction was especially severe in the unprotected organic carbon. The reference and the orchard soils also showed significant differences in the δ13C and δ15N signals, likely due to the different vegetation composition and N dynamics in both areas. Soil properties along a catena, from erosion to deposition areas within the old olive orchard, showed large differences. Soil Corg, Pavail and Norg content, and δ15N at the deposition were significantly higher than those of the erosion area, defining two distinct areas with a different soil quality status. These overall results indicate that the proper understanding of Corg content and soil quality in olive orchards requires the consideration of the spatial variability induced by erosion–deposition processes for a convenient appraisal at the farm scale.

Topographic attributes override impacts of agronomic practices on prokaryotic community structure

“…These and the further observed shifts in soil physiochemical properties between foot-slope and up-slope are in agreement with literature reports, therewith emphasizing the profound potential of slope position in explaining soil edaphic heterogeneity including soil organic C (Lal, 2003;Mayer et al, 2018), moisture (Western et al, 2004), texture (Xu et al, 2016), total C and N, C/N ratio as well as pH (Seibert et al, 2007) at our study site. The erosion/deposition processes reduce the physical protection of SOC at eroding sites and simultaneously accumulate higher C and N contents at the depositional footslope sites (Gómez et al, 2020;Shi et al, 2019). This can explain the higher MWC% and MWN% values determined at our foot-slope plots…”

Significant soil degradation is associated with intensive vegetable cropping in a subtropical area: a case study in southwestern China

“…In this study, the moist composite field samples were air dried and passed through a 1 mm sieve for the analysis of soil pH, CaCl 2 -P, available P (AP), water-soluble K, Ca, and Mg and exchangeable K, Ca, and Mg. The samples were then passed through a 0.15 mm sieve for SOC and TN analysis (Yan et al, 2012;Wang et al, 2014;Gómez et al, 2020). Soil analysis methods for specific parameters and their corresponding soil size preparation standards (described previously) were used in this study (Lu, 2000).…”

“…2a). A higher frequency of tillage operation generally results in the breakup of soil macro-aggregates, soil structure damage (Chivenge et al, 2007;Pires et al, 2017;Six et al, 2000;Gómez et al, 2020), and an increase in soil aeration, which promotes the microbial decomposition of SOC (Sarker et al, 2018). Accelerated SOC decomposition by high air temperatures and soil moisture levels in subtropical regions has been reported (Zhang et al, 2013).…”

“…At the national scale, long-term intensive farming has been shown to cause soil acidification, with an average decline of 0.50 units in pH value in the topsoil of major Chinese croplands from 1980 to 2000 (Guo et al, 2010). Soil acidification is caused by the excessive application of N fertilizers and the loss of base cations via leaching (Guo et al, 2010;Zhang et al, 2016), which leads to decreased crop production and quality (Cakmak and Yazici, 2010). After the conversion from paddy-rape rotation to vegetable cropping, soil pH at all depths decreased, especially 1-3 years after land conversion, by 0.64, 0.68, and 0.40 pH units in 0-20, 20-40, 40-60 cm, respectively (Fig.…”

“…Additionally, high inputs of N fertilizers to vegetable crops and the crop removal of base cations, such as calcium (Ca) and magnesium (Mg), are expected to trigger soil acidification (Guo et al, 2010;Zhang et al, 2016). Nevertheless, according to our preliminary farmer survey in southwestern China, agricultural production commonly received large inputs of Ca and Mg from various fertilizers.…”