Improving the rapid estimation of available nitrogen extracted from soils with an ascorbic acid solution

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  • Azuma Hideo
    Regional Extension Center, Toyama Prefectural Agricultural Technology Division Graduate School of Horticulture, Chiba University
  • Inubushi Kazuyuki
    Graduate School of Horticulture, Chiba University

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Other Title
  • アスコルビン酸溶液抽出法による水田土壌可給態窒素の迅速評価法の検討
  • アスコルビンサン ヨウエキ チュウシュツホウ ニ ヨル スイデン ドジョウ カキュウタイ チッソ ノ ジンソク ヒョウカホウ ノ ケントウ

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<p>We improved the rapid method for estimating available nitrogen (AN) to realize optimal fertilizer management by measuring the total nitrogen (TN) extracted over 16 hours from air-dried paddy soils with a solution including ascorbic acid (AA). Using 11 soil samples from Toyama prefecture after the rice harvest, we measured the TN extracted from 3 g of air-dried soil using 50 mL of solution including AA over 16 hours. The extraction temperatures were set at three levels, and AA with four different concentrations was added to the extracting solution. Results showed that the amount of extracted nitrogen was positively correlated with both extraction temperature and concentration of AA up to 0.1％. The correlation coefficient between AN and extracted TN was the highest when the extraction temperature was set to 50°C and the concentration of AA added to the extracting solution was 0.1％ (r=0.98, p<0.01). A negative correlation was also found between the amount of iron extracted from air-dried soil by 0.1％ AA solution and the ratio of extracted TN to AN when TN was extracted with AA-free water. Furthermore, the amount of TN extracted from air-dried soil with 0.1％ AA solution corresponded to AN at a constant ratio regardless of the amount of iron extracted.</p><p>It was thus concluded that the addition of AA as a reducing agent to the extracting solution in this method increased the extraction of TN. This was because organic nitrogen was extracted not only by heating but also by the reduction of the extracting solution. We were thus able to evaluate the AN quickly and accurately using the TN extracted from air-dried paddy soils over 16 hours with a solution including 0.1％ AA.</p>

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