Influence of Plant Density on the Productivity of Grassland : II. The effects of plant density on the dry matter yield of orchardgrass sward under two cutting frequencies

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  • 草地の生産力に及ぼす個体密度の影響 : 第2報 刈取頻度を異にするオーチャードグラス草地の乾物収量に及ぼす個体密度の影響
  • 草地の生産力に及ぼす個体密度の影響-2-刈取頻度を異にするオーチャードグラス草地の乾物収量に及ぼす個体密度の影響
  • ソウチ ノ セイサンリョク ニ オヨボス コタイ ミツド ノ エイキョウ 2 カリトリ ヒンド オ イ ニ スル オーチャードグラス ソウチ ノ カンブツ シュウリョウ ニ オヨボス コタイ ミツド ノ エイキョウ

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The effects of plant density in combination with two cutting frequencies on the yield of orchardgrass swards were investigated in order to elucidate the appropriate plant density for maintaining high grassland productivity. The variety used for this experiment was "Kitamidori". Orchardgrass was shown in paper-pots in early summer and then transplanted to the experimental field in Sapporo in Semtember 1969. The split plots design was used. Two cutting treatments (3 times a year, 6 times a year) were allocated in main plots and 5 plant densities (11, 44, 100, 178, 400 plants/m^2) were in sub plots. Prior to transplanting, 25g CaO, 20g N, 15g P_2O_5 and 10g K_2O per m^2 were given as basic fertilizer, and furthermore, each of the 20g N, 7.5g P_2O_5, 15g K_2O were topdressed in the second and third years following. The most appropriate density of all was defined as the one beyond which no more in dry matter yield of grass could be expected. The results are summarized as follows ; 1) Under different LAI levels, both NAR and CGR in the low point density were higher than those in the high density as previously reported. Among the main reasons were (1) the lower plant height, (2) the unfavorable production structure, and (3) the lower nitrogen level of blades in the high density as compared with the low density. 2) The regrowth of the plants of the high density was also inferior to those of the low density during summer. In the following are the reasons for it. (1) The dry matter weight of stubble per unit area gained with increasing plant density, while the percentage of TAC and N in the stubble declined. (2) The regrowth root weight per unit weight of stubble and the vitality of root increased with decreasing density. 3) In the three-cut treatment the percentage of plants killed in the second year soared with increasing density. The rate of the dead in the highest density amounted to as much as 65 percent, thus causing a reduction in the dry matter yield. 4) The highest dry matter yield per unit area was obtained in the density of 100 plants per m^2 in the first year and in that of 44 plants per m^2 in the second year, irrespective of cutting treatment. Judging from the results obtained in the present experiment, it was assumed that the appropriate density for keeping high productivity of orchardgrass sward may be around 100 plants per m^2 in such a region as Sapporo.

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