4.2. Effect of sesquioxides and SOC on soil aggregation and cracking
In this study, the soils after oxalate, DCB, and H2O2 treatments released
more fine aggregates, which was coupled with removal of
sesquioxides and SOC. A much less macroaggregates (250–2000 μm)
after H2O2 treatment than that after oxalate and DCB treatments indicated
that the SOC wasmore effective than the sesquioxides in stabilizing
soil macroaggregates (Fig. 2). The result is in line with Peng et al.
(2015) who reported that the H2O2 treatment disruptedmostmacroaggregates
as compared to oxalate and DCB treatments in long-term fertilized
Ultisols. Our analysis also found that the SOC was significantly
correlated with the macroaggregates for both the soils while the
sesquioxides were not (Tables 2 and 3). The result further confirmed
that soil macroaggregates (N250 μm) were bonded togethermostly by organic
materials (Tisdall and Oades, 1982).
For the aggregatessmaller than 250 μm, the sesquioxides rather than
the SOC were the key agents for soil aggregation in the YPF soil with
high Fe/Al oxides (Table 2). Many studies have demonstrated that the