Abstract
The previous paper reported that the characteristic pattern of the production of the pasture established on the mineral soil which was affected remarkably by the invasion of annual weeds, and it was considered that the phenomenon was largely dependent on the edaphic factors derived from the characters of mineral soil. The present paper dealts with the yield of nitrogen, phosphorus, calcium, potassium, magnesium and sodium on the same plots described in the previous paper. The results are summarized as follows: 1) In the yield of six elements, Italian ryegrass had a highly important role from April to Jnue, orchardgrass in July and August and then the annual weeds after September. The group of annual weeds consisted of Echinochloa crus-galli, Setaria viridis, Digitaria adscendens, D. violascens, Amaranthus retroflexus, A. blitum and Achyranthes japonica. The genus Digitaria with its high seedling vigor and high forage production dominated in the grassland excluded almost other plants from summer to autumn. The nitrogen yield of the annual weeds occupied about 50% in the total yield. 2) Nitrogen, phosphorus and magnesium concentrations of plants were affected by the fertilization, although there was negative correlation between magnesium content in plants and dressed potassium. The nitrogen concentration in plants was in the following order ; Trifolium repens>Dactylis glomerata>Lolium multiflorum>Amaranthus retroflexus>A. blitum>Digitaria adscendens>Setaria vilidis. 3) The yields of the phosphorus at the heavy fertilized plot (N 40kg, P_2O_5 20kg K_2O 40kg per 10a) and the light fertilized plot (the half of the heavy fertilized plot) were 5.4kg and 3.8kg P per 10a, respectively. The yield of phosphorus of the annual weeds occupied about 42% in the total yield. 4) Orchardgrass was the highest in the potassium concentration among plant species, Italian ryegrass followed, and the genus Digitaria was the lowest. Accordingly, the great invasion of the annual weeds in pasture lowered the equivalent ratio of potassium to calcium and magnesium in the plants production of pasture. 5) The calcium concentrations of the annual weeds were lower than that of the forages. The ratio of the calcium yield of the annual weeds to the total yield was only 16-30%. 6) Specific difference in the magnesium yields by the forage at the experimental plots having the high level and low level of potassium was shown, the former was 1.97kg, the latter was 2.33kg per 10a. The ratio of the yield of magnesium by the annual weeds to the total yield was shown within 36-53%. 7) The value of K/Ca+Mg milli-equivalent ratio in oats was increased considerably with the increase of dry matter in May. Accordingly, the feeding of dairy cattle by a large quantity of green oats in this season should be taken with a special care.
