Abstract
In the cold climatic district the production of silage corn has been often unstabilized by low solar radiation, low air temperature and the other adverse climatic factors. In this paper we analysed the relationship between the productivity of silage corn and the solar radiation, one of the climatic factors which may influence the productivity strongly. Experiments were carried out over three years, 1977-79, with six hybrids of different maturities in 1977, with two hybrids in 1978 and with nine hybrids in 1979. The treatments of three different light intensities, 100% full sunlight (control), 75% of full sunlight (light shading treatment) and 60% of full sunlight (heavy shading treatment) were applied to plants during different growth stages (early, middle and late growth stage, and the whole growth stage). The shading treatments were conducted under the field condition using the iron frames (3.6m×7.2m×3m in height) covered with white and black shading-cloths. The white cloth reduced the light intensity down to 75% fullsunlight (reduction ratio was 25%) and the black one, 60% full sunlight (reduction ratio was 40%). The plants grown at the density of 5, 330 plants/10 are. The amount of N, P_2O_5 and K_2O supplied were 16〜18kg, 22kg and 18kg/10 are, respectively. The results obtained were as follows ; 1) The silage corn production was strongly affected by the whole stage shading treatments, conspicuously by the heavy shading treatments. At the heavy shading treatments, the aboveground and ear weights decreased down to 52〜80% and 32〜80%, respectively, to those (100%) at the control. While at the light shading treatments the aboveground and ear weights also decreased down to 82〜94% and 76〜94%, respectively. 2) Yields were raised a little higher by the early stage shading treatments than those at the control. On the other hand, the middle stage shading treatments were most effective, decreasing yields conspicuously. That is, the heavy shading treatments applied during the middle stage decreased the aboveground and ear weights down to 69〜80% and 57〜60%, respectively, to those (100%) at the control, while the light shading treatments during the middle stage decreased the aboveground and ear weights down to 89〜94% and 87〜90%, respectively. From the view point of the total solar radiation supplied during the whole growth stage, the ratios of solar radiation cut by the middle stage, light and heavy, shading treatments were no more than 15% and 9%, respectively, nevevertheless, the middle stage shading treatments were crucially effective on the silage corn production. Subsequently to the effect of the middle stage shading treatment, the effect of the late stage shading treatment was largest, that is, the heavy shading treatments decreased the aboveground and ear weights down to 74〜75% and 72〜83%, respectively, to those (100%) at the control. Difference among hybrids used may have been found in the effect of shading treatments on the production.
