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对陕西省的黄绵土、 土和黄揭土进行研究。结果表明，３种土壤的ＮＨ＿４－Ｃａ交换等温线均属“Ｓ”型曲线，其对ＮＨ４＋的选择系数为ｋｃ（４５℃）＞ｋｃ（２０℃）。交换反应的 Ｇ°均为负值而 Ｈ°及Ｓ°均为正值，表明ＮＨ＿４－Ｃａ交换可以自动进行，其反应为吸热反应，交换后离子与土壤结合的有序性降低，土壤对ＮＨ＿４＋的选择性及结合的稳定度都较Ｃａ＿２＋差，对ＮＨ＿４＋的亲和力大小顺序为：黄绵土≥ 土＞黄褐土。
Study on loessial loess, loess and loess in Shaanxi Province. The results showed that all the NH4-Ca exchange isotherms of the three soils belonged to the “S” curve, and the selection coefficient of NH4 + was kc (45 ℃)> kc (20 ℃). G ° of the exchange reaction was negative and both H ° and S ° were positive values, indicating that the exchange of NH_4-Ca could be carried out automatically. The reaction was endothermic and the ordering of ion binding to soil decreased after exchange. The selectivity and binding stability of NH4 + were worse than that of Ca2 +, and the order of affinity for NH4 + was as follows: loessial soil> soil> yellowish brown soil.