Evaluation of nitrogen availability based on the amount of extractable soil organic nitrogen and suggestion for the proper fertilization in rain shelter-grown spinach
2010
Kodashima, R., Kobe Univ. (Japan) | Ae, N. | Matsumoto, S.
Absorbance at 280 nm in soil extracts with 0.4 M sulfate solution was highly correlated with the concentration of total N in the extracts of different soils. Therefore, we proposed an easy detection procedure for evaluating available N in soil. To estimate the total N uptake of spinach grown triannually under a rain shelter, the amount of 0.4 M sulfate-extractable organic nitrogen in the soil was determined before cultivation in the Andosol area in Iwate prefecture, Japan. Total nitrogen uptake of spinach grown without fertilizer in 8 experimental sites showed a tendency to increase when the amount of 0.4 M sulfate-extractable organic nitrogen in soil was increased, while N uptake efficiency tended to decrease when there was over 540 mg/ kg of the extractable organic N in soil. Application of manure compost was effective in increasing the yield, while reducing internal nitrate concentration of spinach. However, the internal nitrate concentration in spinach exceeded the criterion value (3,000 mg /kg) when there was over 540 mg/kg of 0.4 M sulfate-extractable organic nitrogen in soil. These findings indicate that the determination of 0.4 M sulfate-extractable organic nitrogen in soil might contribute to the fertilization of rain shelter house-grown spinach.
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