PLANT ROOT GROWTH IN ACID ANDOSOLS FROM NORTHEASTERN JAPAN

Chemical and greenhouse studies were conducted to show that exchange acidity Y1, determined by titration of 125 ml of N KC1 soil extract (soil:N KC1 = 100:250) with 0.1 N NaOH, was a useful, realistic measure of aluminum toxicity potential in acid Andosols from northeastern Japan. Twenty-eight soil samples consisted of allophane-imogolite soils (11 samples; pH(H2O) 4.6 to 5.9, Y10.4 to 3.1 ml/100g), chloritized 2:1 mineral soils (13 samples; pH(H2O) 3.9 to 5.0, Y16.8 to 38.2 ml/100g), and allophane-imogolite-chloritized 2:1 mineral soils (4 samples; pH(H2O) 4.6 to 5.3, Y13.3 to 5.0 ml/100g). Three test plants, burdock cv. Takinogawa (Arctium lappa), barley cv. Norin-24 (Hordeum vulgare), and dent corn cv. Choko-1 (Zea mays), were grown on these soils in a greenhouse, and their root length and acid-injury were observed. Root length of all the test plants had a significant relationship with exchange acidity Y1, shown by exponential equations. Degrees of acid-injury determined by root length and root morphology were also closely related to exchange acidity Y1. Chloritized 2:1 mineral Andosols had “critical” pH(H2O) of about 5.0 and “critical” pH(KCl) of about 4.5, whereas allophane-imogolite Andosols did not have these “critical” pHs and did not restrict the root growth greatly even at low pH(H2O), such as 4.6.