野山의 新開墾地土壤과 次山灰土壤에 있어 特히 問題가 되는 燐酸의 施肥量 決定의 한 基準인 燐酸吸着力의 測定方法을 檢討할 目的으로 火山灰土壤과 鑛質土壤(未耕地및 旣耕地土壤)에 對하여 燐酸吸着에 關한 試驗을 行하였는바 그結果를 要約하면 다음과 같다. 1. Langmuir 吸着式을 利用하여 求한 燐酸의 最大吸着量은 旣耕地土壤 6.2∼32.9, 未耕地土壤 74.1∼90.4, 火山灰土壤 720∼915㎎.p/100g 이였다. 2. 燐酸吸收係數는 旣耕地土壤에서 116∼179, 未耕地土壤에서 161∼259, 火山灰土壤에서 1,098∼1,205㎎.p/l 이며, 燐酸吸收係數/Langmuir 最大吸着量의 比는 燐酸吸着力이 큰 火山灰土壤에서 적고 (1.3∼1.5) 燐酸吸着力이 낮은 土壤일수록 컸다. (2.2∼18.7) 3. 燐酸吸收係數의 測定은 高濃度의 燐酸溶液에서 行하여 지므로 이로서는 石灰 또는 燐酸施用에 依한 吸着量의 變動을 明確히 推定하기 어려우나, 低濃度에서 測定한 濃度別 燐酸吸着量및 Langmuir吸着式을 利用하여 求한 最大吸着量으로서는 吸着量의 變動推定을 分明히 할 수 있었다. 4. 置換性 알루미늄을 中和하기 위한 當量의 水酸化칼슘을 加하여 圃場容水量에서 40日間 恒溫(25∼30℃) 處理하므로서 置換性 알루미늄 含量이 높은 鑛質土壤에서는 Langmuir 最大吸着量이 有意한 減少를 보였다. 5. 燐酸을 處理하여 50일간 圃場容水量 상태에서 恒溫(25∼30℃) 處理한 土壤에 對하여 Langmuir最大吸着量을 測定한바 最大吸着量에 相當하는 燐酸의 施用으로 火山灰土壤은 25.5 未耕地土壤은 54.4%, 旣耕地土壤은 76.2%의 飽和率을 나타내었다. 6. 土壤의 燐酸吸着量은 添加燐酸의 濃度가 높아짐에 따라 曲線的으로 增加하여 어느 一定濃度에 이르면 吸着飽和點에 達하며 鑛質土壤에서는 100㎎.p/l, 火山灰土壤에서는 1,000㎎.p/l의 燐酸溶液으로 測定되는 燐酸吸着量은 Langmuir最大吸着量에 매우 近似한 값을 나타내므로 이를 土壤의 燐酸吸着力을 나타내는 새로운 指標로 삼고 飽和吸着量이라 定義하였다. 7. 單一濃度에서 이루어지는 飽和吸着量의 測定으로 여러 濃度에서 燐酸의 吸着量을 求하여야 하는 Langmuir 最大吸着量 測定의 煩雜性을 避할 수 있어 이 方法은 實用的인 方法으로 判斷되었다.

Laboratory experiments on the phosphorus adsorption by soil were conducted to evaluate the parameters for determination of phosphorus adsorption capacity of soil, which serve as a basis for establishing the amount of phosphorus required to improve newly reclaimed soil and volcanic ash soil. The calculated Langmuir adsorption maxima varied from 6.2-32.9, 74.7-90.4 and 720-915㎎ p/100g soil for cultivated soils, non-cultivated soils, and volcanic ash soils respectively. The phosphorus absorption coefficient ranged from 116-179, 161-259 and 1,098-1,205㎎ p/100g soil for cultivated soils, non-cultivated soils, and volcanic ash soils respectively. The ratio of the phosphorus absorption coefficient to Langmuir adsorption maximum was low in soils of high phosphorus adsorption capacity (1.3-1.5) and high in soils of low phosphorus adsorption capacity (2.2-18.7). Changes in the amount of phosphurus adsorption induced by liming and preaddition of phosphorus were hadly detected by the phosphorus absorption coefficient, which is measured using a test solution with a relatively high phosphoru, concentration. The Langmuir adsorption maximum was a more sensitive index of the phosphorus adsorption capacity. The Langmuir adsorption maxima of the noncultivated soils, which were treated with an amount of calcium hydroxide equivalent to the exchangeable Al and incubated (25-30℃) for 40 days at field capacity, were lower than the original soils. The change in the adorption maximum on incubation following the liming of soils was insignificant for other soils. The secondary adsorption maximum of soils, which received phosphorus equivalent to the Langmuir adsorption maximum of the limed soils incubated (25-30℃) for 50 days at held capacity, was 74.5, 5.6 and 23.8% of the primary adsorption maximum for volcanic ash soils, noncultivated soils, and cultivated soils respectively. The amount of phosphorus adsorbed by soils increased quadratically with the concentration of phosphorus solution added to the soils. The amount of phosphorus adsorbed by 5-g soil samples from 100㎖ of 100- and 1,000㎎ p/l solution for the mineral soils and volcanic ash soils respectively was found to be close to the Langmuir adsorption maximum. The amount of the phosphorus adsorbed at these concentrations is defined as a saturation adsorption maximum and proposed as a new parameter for the phosphorus adsorption capacity of the soil. The evaluation of the phosphorus adsorption cap acity by the saturation adsorption maximum is regarded as a more practical method in that it obviates the need for the various concentrations used for the determination of the Langmuir adsorption maximum.