Relation between characteristics of grassland soils and climatic factors on the Kuju Plateau, Japan and the effect of liming on the growth of Italian ryegrass and soil acidity

抄録

　　The acidic surface soil of non-allophanic Andosols may affect grass growth in grassland. In the Kyushu region of Japan, non-allophanic Andosols are mainly concentrated on the Kuju Plateau in Oita Prefecture. This study aimed to investigate the effect of climatic factors on the distribution of non-allophanic surface soils, clarify the surface soil acidity of grasslands, and evaluate the effect of liming on the early growth of grasses and on the soil chemical properties. The surface soils of 17 out of 27 sites in 25 grassland fields had the ratio of sodium pyrophosphate-extractable Al to acid ammonium oxalate-extractable Al (Al_p/Al_o) ≧ 0.5 which is a non-allophanic characteristics. Moreover, 15 out of the 17 sites had a Thornthwaite’s P-E (precipitation–evapotranspiration) index ≧ 200, which indicates low temperatures and high precipitation. Ten sites of non-allophanic soil and two sites of allophanic soil were acidic with an exchangeable acidity (y₁) of ≧ 3. Pot experiments showed that liming the acidic soils to create y₁ < 3.0 improved the early growth of Italian ryegrass and significantly decreased the amount of exchangeable Al and organic bound-Al in the soil. These findings suggested that y₁ of 3, used as a target value for acidity management of grassland in Niigata Prefecture, could also be applied on the Kuju Plateau, regardless of the type of Andosol.