The influence of pH, ionic strength, ligands (Cl, SO4, PO4), and metals (Ni and Pb) on the adsorption of Hg(II) by quartz and gibbsite was investigated to better understand the Hg(II) adsorption process and the impact of metals and ligands on this process. The triple layer model (TLM) was used to simulate Hg(II) adsorption on both surfaces. Mercury(II) adsorption from a 0.6 μM Hg(II) solution varies as a function of pH, increasing to an adsorption maximum with increasing pH before tailing off to a constant level at high pH values. The pH at which maximum Hg(II) adsorption occurs (pHmax ≈ 4.5) is comparable to the pKa (3.2) for the hydrolysis of Hg2+ to form Hg(OH)02 Further, the Hg(II) adsorption edge shifts to much higher pH values in the presence of 0.001 M and 0.01 M Cl, which also corresponds to the pH at which Hg(OH)02 is predicted to form. Only minor deviations in the degree of adsorption and the shape of the Hg(II) adsorption edge are influenced by ionic strength, suggesting the formation of inner‐sphere surface complexes. However, Hg(II) adsorption can only be successfully modeled with consideration of the formation of both an outer‐sphere surface complex [≡XO−–HgOH+] and an inner‐sphere surface complex [≡XOHg(OH)−2]. Swamping concentrations (0.01 M) of SO4 and PO4 reduced Hg(II) adsorption on quartz, a result of the predicted formation of Hg(OH)2SO2−4, Hg(OH)2H2PO−4, and Hg(OH)2–HPO2−4 aqueous species (the adsorption edge and pHmax were not influenced). The presence of SO4 also decreased Hg(II) retention by gibbsite, which was also attributed to the formation of the Hg(OH)2SO2−4 ion pair; however, the presence of PO4 increased Hg(II) retention by gibbsite, which was attributed to the formation of a phosphate bridge [≡AlOPO3Hg(OH)2−2]. Mercury(II) adsorption was decreased in the presence of 14 μM Pb and 48 μM Ni, and most noticeably in the quartz system. The adsorption of Hg(II), when in competition with Pb or Ni, could not be simulated by the TLM without the reoptimization of the Hg(II) outer‐ and inner‐sphere log Kint values. Intrinsic Hg(II) adsorption constants derived from single‐element systems could not be employed to simulate adsorption in multi‐element, competitive systems.

Adsorption of Hg(II) by kaolinite was investigated as a function of solution pH, ionic strength, and the competitive or complexation effects of ligands (Cl, SO4, PO4) and metals (Ni and Pb). Mercury(II) adsorption from a 0.6 μM Hg(II) solution was primarily influenced by pH. The Hg(II) adsorption edge was described by a pH50 (pH where 50% adsorption occurs) of 3.4 and a pHmax (pH where maximum adsorption occurs) of 4.4. At pH values above the pHmax, Hg(II) retention decreased with increasing pH. Chloride and Ni shifted pH50 from 3.4 to 7 and 4.1, respectively. Nickel and Pb reduced the amount of Hg(II) adsorbed throughout the pH range examined. Ionic strength and the presence of SO4 and PO4 had relatively little impact on the Hg(II) adsorption envelope. The adsorption of Hg(II) was predicted through the application of the triple layer model (TLM) by assuming that the kaolinite surface was composed of equal proportions of silanol and aluminol groups. The TLM model suggests that the silanol group was responsible for retaining the bulk of the adsorbed Hg(II), through the formation of the ≡SiO−‐HgOH+ outer‐sphere, and the ≡SiOHg OH−2 and ≡SiOHgCl0 or ≡SiOHgOHCl− (Cl system) inner‐sphere species. The ≡AlO−‐HgOH+ outer‐sphere complex accounted for a small percentage (<15–35%) of the adsorbed Hg(II). The TLM results suggested that Hg(II) adsorption by both ≡SiOH and ≡AlOH sites on kaolinite should be considered to predict adequately Hg(II) retention.

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Information on nitrogen (N) fertilization of no‐till (NT) cotton (Gossypium hirsutum L.) is needed to optimize lint yields and earliness. We evaluated five N rates and three application methods for NT cotton production on Loring silt loam (fine‐silty, mixed, active, thermic Oxyaquic Fragiudalfs) with natural winter annuals as a cover; and on Memphis silt loam (fine‐silty, mixed, active, thermic Typic Hapludalfs) having corn (Zea mays L.) stover as a cover and on Lexington silt loam (fine‐silty, mixed, active, thermic Utlic Hapludalfs) having winter wheat (Triticum aestivum L.) as a cover. Nitrogen rates of 0, 34, 67, 101, and 134 kg ha−1 were either broadcasted as ammonium nitrate (AN) or injected as urea–ammonium nitrate (UAN) at planting. Additional treatments included broadcasting 67 kg N ha−1 as AN at planting with either 34 or 67 kg N ha−1 banded 6 wk later. Relative to no N, broadcasting 67 kg N ha−1 as AN increased 4‐yr average NT lint yields on Loring silt loam from 739 to 1281 kg lint ha−1 and 2‐yr average yields on Lexington silt loam from 1086 to 1535 kg ha−1. A higher N rate (101 kg N ha−1) was needed to increase 2‐yr average yields on Memphis silt loam from 821 to 1169 kg ha−1. Broadcasting AN was a satisfactory placement method producing yields equal to or higher than injecting UAN or splitting AN for NT cotton produced on these loessial soils despite different covers and residues.

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