Organomineral Interactions and Herbicide Sorption in Brazilian Tropical and Subtropical Oxisols under No-Tillage

We evaluated the effects of the soil
organic matter (SOM) composition,
distribution between soil aggregates size, and their interactions
with the mineral phase on herbicide sorption (alachlor, bentazon,
and imazethapyr) in tropical and subtropical Oxisols under no-till
systems (NT). Using soil physical fractionation approach, sorption
experiments were performed on whole soils and their aggregates. SOM
chemistry was assessed by CP/MAS 13C NMR. The lower sorption
observed in tropical soils was attributed to the greater blockage
of SOM sorption sites than in subtropical soils. When these sites
were exposed upon physical fractionation, sorption of the three herbicides
in tropical soils increased, especially for imazethapyr. High amounts
of poorly crystallized sesquioxides in these soils may have contributed
to masking of sorption sites, indicating that organomineral interactions
may lead to blockage of sorption sites on SOM in tropical soils.