The Effects of Subsoil Acidity of Andosols on the Yield and Botanical Composition of Legume-Grass Mixture : 1. Growth of Alfalfa-Orchard Grass Mixture

Abstract

A field study was conducted to clarify the effects of subsoil acidity of Andosols on the yield and botanical composition of alfalfa-orchard grass mixture for three years. Two kinds of unreclaimed Andosols were used for the subsoils of experimental plots: very strongly acid Kawatabi soil (non-allophanic) and weakly acid Zao soil (allophanic). Root growth of alfalfa was severely precluded by Al toxicity in non-allophanic subsoil but normal in allophanic subsoil. In contrast, orchard grass showed normal root growth both in allophanic and non-allophanic subsoils. Inorganic nigrogen derived from basal ammonium sulfate moved easily toward subsoils because of high rainfall in autumn. Consequently, in early growing stage, alfalfa grown in non-allophanic soil plot showed severe nitrogen deficiency and drustic reduction of dry matter. During dry summer, the alfalfa in the non-allophanic soil plot showed severe "Wilting" symptom than that in allophanic soil plot when available soil water in the limed surface soil is exhausted. Dry matter yield of alfalfa in non-allophanic soil plot was much less than that in allophanic soil plot. In contrast, the dry matter yield of orchard grass was rather greater in non-allophanic soil plot. The proportion of alfalfa to total yield was higher in allophanic soil plot than in non-allophanic soil plot throughout experimental period. The present study showed that subsoil as well as surface soil plays an important role in supplying both water and nutrient for grasses.