Abstract
Field investigation on plant and soil potassium was carried out in grazing pasture and in meadow of mineral soil. The results obtained were as follows ; 1. Plant potassium content in the grazing pasture was higher than in the meadow of all the species of the forage plants (Italian ryegrass, orchardgrass, tall fescue, alfalfa, red clover and white clover) and of a weed (Wild common vetch). Among the forage plants, white clover and tall fescue showed the highest and the lowest potassium content, respectively. 2. Monthly change of potassium content in the forage plants grown on the orchardgrass grazing pasture was larger (5.8-1.5% on a dry matter basis) than that on the tall fescue grazing pasture (3.8-2.0%). Potassium contents of the several weeds in the meadows fenced from the grazing pastures varied in the ranges of 5.9 to 1.9%. 3. Monthly change of the exchangeable soil potassium content in the orchardgrass grazing pasture was almost the same as that in the tall fescue grazing pasture. There was no significant correlation between the forage potassium content and the exchangeable soil potassium content in both grazing pastures. 4. There was a positively significant correlation at 5% level between the forage potassium content and the exchangeable soil potassium content in the orchardgrass meadow when the soil potassium content was in the range of 10 to 65 mg/100 g. However, such a significant correlation disappeared in the case that the soil potassium content was in the narrower range as 10 to 25 mg/100 g. 5. The forage potassium content in the orchardgrass grazing pasture strongly responded to the potassium application more than that in the tall fescue grazing pasture. However, the soil in the former pasture had contained enough amount of potassium to meet the requirement of the forages. These facts suggest that the forage potassium content did not act as a limiting factor for the forage growth in the orchardgrass grazing pasture.
