Studies on the Relation between the Tolerance of Crops to Soil Acidity and That to Low pH : (15) The effects of aluminum, hydrogen ion, lime, magnecium, nitrate and nitrite of varying concentrations on the growth of Italian ryegrass and milk vetch.

Abstract

In order to find out factors in Kuroboku of acidic soil injurious to the growth of Italian ryegrass and milk vetch, water cultivation was carried out. The results are as follows: (1) Hydrogen ion concentration: Even Italian ryegrass, which is moderately tolerant to the acidity of soil, the yield showed decrease, when the pH in the culture solution was lowered to 4.3. At pH 4.3, the percent content of calcium and phosphorus on dry weight basis was suppressed. In the culture solution at pH 4.3 the growth of milk vetch markedly decreased and the percent content of calcium and potassium was suppressed. On the other hand, the yield of milk vetch also decreased, when pH value was raised from 5.3 to 6.3. The percent content of inorganic matter was decreased, similarly to the phenomenon observed at pH 4.3. This might be one of the cause for the low yield of milk vetch on slightly acidic soil. (2) Aluminum: Aluminum at the concentration of as low as 0.5 ppm inhibited the growth of milk vetch. However the same concentration of aluminum promoted the plant growth of Italian ryegrass. For both of the forage crops, the dry weight percentage of phosphorus was severely suppressed and their growth was strongly reduced by the aluminum concentraction of 5 ppm. For milk vetch, the suppression of the dry weight percentage of calcium, potassium and magnesium was also observed. In this experiment, the decrease of phosphorus uptake was probably largely due to the precipitation of calcium phosphate in the culture solution. (3) Lime: The low concentration of both lime and magnesium was highly injurious to the growth of plant. The optimum concentration of calcium in the culture solution of milk vetch was higher than that of Italian ryegrass. According as the concentration of lime in the nutrient solution has increased, calcium percentage in the top also increased, Magnesium content in both plants dereased under this condition. However, suppression of phosphorus percentage was observed only in the case of milk vetch. Potassium percentage has increased when the concentration of lime in the nutrient solution was raised from low level to standard level. However potassium percentage in Italian ryegrass greatly has increased when the concentration of both lime and magnesium in the nutrient solution was lowered. (4) Magnesium: The optimum concentration of magnesium in the culture solution for milk vetch was lower than that for Italian ryegrass. When concentration of magnesium in the culture solution was low, lime, phosphorus and patassium percentage in the dry matter of Italian ryegrass were also low, but calcium percentage of milk vetch was increased. On the other hand, when magnesium concentration showed increase from standard level to high level, calcium percentage decreased to a level of lime defficient value and phosphorus and potassium percentage also decreased at the same time. (5) Nitrate: The optimum concentration of nitrate nitrogen in culture solution was low for milk vetch, and the yield decreased markedly according to the heightened concentration of nitrate nitrogen. This fact is thought to be the cause for the crop decrease in the case of weakly or slightly acidic soil. The increasing supply of nitrate reduced the growth severely, accompanied by the decrease in the starch content in leaf blades. Thc optimum concentration of nitrate nitrogen in the culture solution for Italyan ryegrass was higher and so much difference was not found in the starch content in leaf blades, when the concentration of nitrate was varied. (6) Nitrite: Nitrite nitrogen in culture solution was injurious to the growth of milk vetch at the low concentration of 2 ppm. However the growth of Italyan ryegrass was promoted at the same concentration, suggesting the high tolerance of this plant to the nitrite nitrogen.