Studies on the Relation between the Tolerance of Crops to Soil Acidity and That to Low pH : (13) Studies on the cause for the extinction of forage crops sown in untilled grassland

Abstract

Seeds of four forage crop plants were sown on untilled grassland of various pH value with varying lime nitrogen application. (1) The growth of forage crop plants sown on untilled acidic grassland, primarily depends, when the weeds were few, upon the chemical property of the soil which was changed with pH value. In the plots of denser weed population, however, sunlight was insufficient for the growth. In very heavily shaded plots, forage crop could not survive. The growth of forage crop was primarily related to the amount of sunlight at 1 to 2 cm, above the soil surface. (2) Wild grasses having thickly arranged, wide leaves intercepted sunlight more strongly. Among the same species, the taller weed plants intercepted more sunlight. The taller forage crops received less damage than the shorter ones. (3) Growth of both forage crops and wild grasses was smaller on the soil of lower pH value. The experiment plots, highly acidic grassland of organic volcanic ash soil, were deficient in N, P, Ca, and K, and were excessive in Al. When lime nitrogen was applied to such plots, the soil was still deficient in P and K in the upper layer of soil. As the change of pH values of soil, induced by the dispersion of lime nitrogen on soil surface, was seen only within the depth of 0-6 cm, the growth of perennial weed plants with deep rhizomes was largely influenced by the fertility before dispersion. Cogon grass, which was tolerant to soil acidity, grew vigorously when the soil was rich in NO₃-N.