Organic matter distribution in aggregate sizes of a mollisol under contrasting management

Abstract

Total and particulate organic matter content in different aggregate sizes can be used as an indicator of land use effect. We hypothesized that tillage reduction increases total (SOC) and particulate soil organic C (POC) contents and the stability of larger aggregates of high-SOC-content Mollisols. Three management systems (continuous pasture (Pp), and continuous cropping under conventional tillage (CT) and notillage (NT)) were evaluated. Oven dried soil samples (0-5 and 5-20 cm), were wet sieved through 2000, 250 and 50 µm sieves after immersion (IW) and capillary (CW) wetting. Particulate organic matter (>50 µm) was separated in both the whole soil and in each aggregate fraction, SOC and mineral associated organic C contents were determined, and POC was calculated by subtraction. Reduced soil disturbance (Pp and NT) yielded more SOC and POC in the whole soil and macroaggregates with higher stability (Pp>NT>CT). Under Pp, macroaggregates showed the highest SOC and POC. Under NT, macroaggregates showed higher SOC and POC and aggregate stability than CT though lower than Pp. Less tillage-induced disruption (Pp and NT) led to higher SOC and POC contents in more stable macroaggregates but continuous no-tillage appeared not to be enough to reverse the effects of long lasting conventional management practices on these Mollisols.

Separation of soil microbial community structure by aggregate size to a large extent under agricultural practices during early pedogenesis of a Mollisol

“…2). The same distribution pattern was observed for the Mollisol in the same region and in other regions (Chen et al, 2010;Mandiola et al, 2011) and for different soil types (Elliott, 1986;Oades and Waters, 1991;Guggenberger et al, 1999;Six et al, 2000a,b;Väisänen et al, 2005;Wright and Hons, 2005). Their results corroborated the hierarchical concept of soil aggregation, according to which microaggregates are bound into macroaggregates by labile organic matter, resulting in higher SOC in macroaggregates than in microaggregates.…”

Fire and Tillage as Degrading Factors of Soil Structure in Northern Zagros Oak Forest, West Iran

“…Bronick and Lal () reported that macroaggregates are more vulnerable to environmental changes than microaggregates, because macroaggregates are chiefly bound together by impermanent binding agents, such as polysaccharides, roots, and hyphae, while microaggregates are held together by more persistent binding agents, such as strongly sorbed organic polymers, oxides, and polyvalent cations. In agreement with our findings, Andreu et al () showed the degradation effect of high temperatures on macroaggregates and the parallel increase in microaggregates, particularly the <1‐mm ones, while a deleterious effect of conventional agriculture compared to continuous pasture or cropping under no‐tillage on soil macrostructure (>2 mm) to advantage of lower size aggregates was demonstrated by Mandiola et al (). The selective detrimental impact of cultivation on macroaggregates to advantage of microaggregates was assessed by several other authors (e.g.…”

Effect of glyphosate application on soil quality and health under natural and zero tillage field condition

“…Despite the coarser texture of samples RF1 and RF2, a strong correlation between POM and WSA (r = 0.97) indicated that the higher contents of ECa and POM (Table 2) could be responsible for cementing the soil particles (Horn et al 1994;Paradelo et al 2013). Differences between the maximum values of WSA (RF1 and RF2) and the lowest (RF4 and RF5) could be attributed to farming since it reduces the soil's POM content (Mandiola et al 2011). Nonetheless, even though RF3 was from a natural condition soil, it showed a medium value of WSA, indicating a reduction of soil stability that could be due to a chemical perturbation caused by glyphosate input, for the only difference between RF3 and its pairs RF1 and RF2 was a higher exposure to glyphosate.…”