Abstract
Growth disorder often occurs in the early stage of sugar beet. This happens not only in paper-pot planting but in direct sowing cultivation as well. We investigated the actual condition of growth disorder in field and elucidated the chemical factors related with growth disorder in soil condition. 1) In paper-pot planting cultivation, growth disorders did not occur just after transplanting (transplanting: from the middle of April until early in May) and were first recognized in June, then spread partially or extensively in field. Growth was apparently delayed but seemed to be recovered on the surface thereafter in many cases. The dead plant was very rare. In the direct sowing cultivation, growth disorders did not occur just after shooting (sowing: from the middle of April until early in May) and occurred first in June. Typical symptoms of disorder were delay of growth, yellowing of new leaves, reddening of the edge of leaves and shortening and browning of roots. In severe cases plants disappeared in wide spaces. 2) In paper-pot planting cultivation, soil pH and degree of Ca and base saturation in soils where disorders occurred were significantly lower than those in normal fields. On the contrary exchangeable acidity (y_1) of disordered fields was apparently higher than that of normal fields. Leaf length in July and final root yield were closely related with these chemical properties (soil pH, degree of Ca and base saturation and exchangeable acidity (y_1)). These results showed that the main cause of growth disorders in early stage of paper-pot planting was derived from soil acidity. 3) In the direct sowing cultivation, soil pH and degree of Ca and base saturation in soils where disorders occurred were significantly lower than those in normal fields. Exchangeable acidity (y_1) of disordered fields was significantly higher than that of normal fields. But in some cases, growth disorders were observed even in reasonable soil pH, more than 5.5. This suggested that the cause of growth disorders in direct sowing cultivation might involve other complicated factors. But the main factor that caused growth disorder seemed to be derived from soil acidity. 4) Year by year the soil in upland fields became acidic in Hokkaido. This promoted the appearance of growth disorders in many fields of sugar beet cultivation. So it is important to maintain the soil acidity in sugar beet cultivation.
