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Twelve Oxisols from the Triangulo Mineiro region, Minas Gerais state, Brazil, derived from four different parent materials were studied to provide insight into their Fe‐oxide mineralogy. The clay fraction (<2 µm) of all soils consisted of kaolinite and Fe oxides (hematite and/or goethite); gibbsite and anatase were found in most of the soils; maghemite was detected in several of them. Citratedithionite (CD) treatment of the soil clays showed hematite preferentially dissolved compared with goethite, and a higher dissolution rate for poorly crystalline than for well‐crystalline goethite. The calculated values for Al substitution in the Fe oxides, based on the CD extracts of the total clay corrected for Al soluble in acid ammonium oxalate, and of clay treated for gibbsite removal gave fair to good agreement with Al substitution determined by differential x‐ray diffraction (DXRD) for those samples in which the Fe‐oxide fraction was dominated by either goethite or hematite. Aluminum‐substituted maghemite, detected by DXRD, was present only in soils from mafic rocks, suggesting its formation through oxidation of the magnetite present in the parent material. Aluminum substitution, determined by DXRD, varied from 17 to 36 mol % for goethites, 6 to 15 mol % for hematites, and 16 to 26 mol % for maghemites. The mean crystallite dimension (MCDkkl) of some hematite samples determined from DXRD showed preferential crystal development in the X‐Y direction, suggesting a platy nature.

In an attempt to reduce NO3−‐N movement to drainage waters, flashboard riser‐type water level control structures were installed in tile mains or outlet ditches at two locations to raise the water table to increase denitrification during the winter. A large reduction in NO3−‐N movement through tile lines occurred (from 25–40 to 1–7 kg/ha) in moderately well‐drained soils because of reduction in effluent volume. In the moderately well‐drained soils, there was no indication of increased denitrification in the field. In poorly drained soils, drainage control had no influence upon soil profile oxidation‐reduction potentials but resulted in approximately.a 50% reduction in NO3− movement through drainage ditches. This reduction was due to increased water movement into and through deeper soil horizons (below 1 m). The NO3−‐N concentrations and low Eh values in all profiles below 1 m indicate that the NO3− which moved to this depth underwent denitrification.

The adsorption of sevens-triazines from aqueous solutions by organic soil colloids was determined at pH levels from 1.0 to 5.2. Maximum adsorption occurred at pH levels in the vicinity of the pKAvalues of the respective compounds. The amounts adsorbed were dependent upon the molecular structures of the compounds and the pH of the suspension and were, in order of decreasing adsorption, as follows: 2-methoxy-4,6-bis(diethylamino)-s-triazine (hereafter referred to as tetraetatone) = 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne) = 2-hydroxy-4,6-bis(isopropylamino)-s-triazine (hereafter referred to as hydroxypropazine) > 2-methoxy-4-diethylamino-6-ethylamino-s-triazine (hereafter referred to as trietatone) > 2-methoxy-4,6-bis(isopropylamino)-s-triazine (prometone) > 2-methoxy-4,6-bis(ethylamino-s-triazine (simetone) > 2-chloro-4,6-bis(isopropylamino-s-triazine (propazine). Approximately 52% of the prometone adsorbed by the organic matter was desorbed with two extractions of 0.1N NaCl. It was concluded that the adsorption of thes-triazines was due to complexing of the triazine molecules with functional groups on the organic colloids and/or adsorption ofs-triazine cations by ion exchange forces.