2013 Volume 12 Issue 1 Pages 43-49
Soil diagnosis was used to reduce the amount of nitrogen fertilizer and plant nitrate concentration in a year-round cultivation of komatsuna (Brassica rapa L. Perviridis Group) in a greenhouse. The amount of nitrogen fertilizer in the control was based on the plant-assimilated nitrogen. The soil nitrate-nitrogen content was tested before fertilization and subtracted from two standard amounts of nitrogen fertilizer. That in Method-I was the amount of the control, and the amount of nitrogen mineralized from the soil in Method-II was subtracted from the amount of the control. Total amounts of nitrogen fertilizer used during the five seasons were 20.0, 9.5, and 4.4 g·m−2 for the control, Method-I, and Method-II, respectively. At lower temperatures, the plants grew slowly and the amount of nitrogen from the soil was lower. Yields were similar with all methods, although the leaves were paler than in the control with Method-I and II during spring and summer. The plant nitrate concentration with all methods was <1,000 mg·kg−1 during winter and spring; with the control, it was >2,500 mg·kg−1 in summer and autumn; and with Method-I and II, it was <500 mg·kg−1 in summer and approximately 2,300 and 800 mg·kg−1, respectively, in autumn. These results indicate that both methods reduced the amount of nitrogen fertilizer and plant nitrate concentration.
