| Abstract: | (pp. 9–16) Nitrate is a major form of uptake and storage of nitrogen for upland plants. However, nitrate is harmful to human health · ingestion of a large quantity can lead to cancer or methemoglobinemia. The effectiveness of drip fertigation for reducing nitrate in spinach was investigated in this study. Fertilizer application can be controlled effectively by drip fertigation. Field experiments were conducted in September 2002 and June 2003 at the National Agricultural Research Center for Hokkaido Region. Two spinach cultivars were grown in each cultivation in a plastic greenhouse, and the plants were treated with 4, 8 or 12 g N m?2 of fertilizer applied by drip fertigation, and with 8, 12 or 16 g N m?2 of fertilizer applied as basal application. The nitrogen was applied at the rate of 0.15 g m?2 per day for the first 15 days, and 0.25 g m?2 for the following 23 days in 8 g N m?2 treatment of drip fertigation. The rate of growth and nitrogen absorption of spinach in the early growth stages was very slow, but they increased quickly from around day 23 after sowing. The amount of nitrogen absorbed by spinach was close to the amount applied in 8 g N m?2 treatment. This treatment resulted in spinach with a low nitrate concentration without reduction in yield. Although the same results were obtained by treatment with 8 g N m?2 of fertilizer by basal application, there was a tendency for nitrate concentration to fall further with drip fertigation. The rate of nitrate-nitrogen to total-nitrogen rose sharply when the total-nitrogen concentration was higher than 42 g kg?1 DW in leaf blade and 18 g kg?1 DW in leaf petiole. The total-nitrogen concentration was lowered a little and for that reason the rate of nitrate-nitrogen to total-nitrogen was lower in spinach treated with 8 g N m?2 of drip fertigation than in spinach treated with 8 g N m?2 of basal application. Thus, drip fertigation was considered to reduce nitrate more stably. |
