Reduction of heat damage in cabbage by planting on the northern slope in ridge rows, and available hydro-characteristics of cultivars for use

Cabbages to be harvested in the year-end season are transplanted in the previous summer, and frequently receive heat damage in their early period of growth. Aiming to reduce the damage, a cultural practice of transplanting on the northern slope of the ridge rows with their direction running east-west was evaluated. Temperature was decreased and water content was increased in the soil under the northern slope of the ridge rows. Leaf area increasing in the early period of growth between the northern slope and the conventional top-planting were analyzed in eight cultivars in a summer planting. The planting on the northern slope accelerated the leaf area increase in most of the cultivars, however the increase in the ratio of the northern slope to the top differed largely in the cultivars. The hydro-physiological characteristics of the higher ratios were analyzed in cultivars, comparing the xylem pressure potential vs. water content relation. The cultivars with high ratios held water much better in their bodies under the water stressed condition, showing high tolerance to drought. The effect of the tolerance appeared earlier in these cultivars transplanted on the northern slope of ridge rows than in those transplanted on the top, affected by the characteristics of their pressure-volume curves. Growth and yield in eight cultivars which had been planted on the slopes were compared to the top-planting in different cropping seasons. The northern slope planting was superior to the top-planting in the late spring, summer and early autumn transplanting, while inferior to that in the middle autumn. The largest disappointment of the northern slope planting was the flooding damage in the hot season. We confirmed the significant effect of a model of paper-pot transplanters for transplanting on the slope of ridge rows.