Water extractable organic carbon and nitrogen and their stable isotopes from long-term experiment in a Japanese rice paddy
Authors: Nguyen-Sy Toan , Cheng Weiguo , Guigue Julien , Munyaka Kimani Samuel , Aji Wibowo Wisnu , Tawaraya Keitaro , Watanabe Toru , Wu Ji , Xu Xingkai 
Published: July 2020

<span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">Hot water- and water-extracted organic matter was extracted from soil samples collected after a 31-year long-term experiment which aimed to assess the effect of different fertilization strategies (inorganic fertilizers and organic matters) commonly used for paddy rice cultivation in Yamagata, northeastern Japan. </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">The ratio of soil to </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">extracted</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US"> water was 2:3. </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">The amounts of hot water-extracted organic carbon and nitrogen (HWEOC and HWEN) at 80 <sup>o</sup>C and 16 hours, water-extracted organic carbon and nitrogen (WEOC and WEN) at room temperature, and their δ<sup>13</sup>C and δ<sup>15</sup>N were measured from the five fertilizer treatment plots as [1) PK, 2) NPK, 3) NPK + 6 Mg ha<sup>-1</sup> rice straw (RS), 4) NPK + 10 Mg ha<sup>-1</sup> rice straw compost (CM1), and 5) NPK + 30 Mg ha<sup>-1</sup> rice straw compost (CM3)], for surface (0-15 cm) and subsurface (15-25 cm) layers. HWEOC and WEOC accounted for an average of about 1.5</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">1</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US"> and 0.66% of SOC, while HWEN and WEN accounted for an average of about 1.09 and 0.40% of soil TN, respectively. About 90% of the extracted N was organic form</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US"> among all treatments</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">. The values of δ<sup>13</sup>C for HWEOC and WEOC ranged from -28.2 to -26.</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">5</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">‰ and from -28.3 to -27.0‰, similar to the original rice straw and rice straw compost</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">, and lower than the value of original soil at -22.5</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">‰. The values of δ<sup>15</sup>N of HWEN, WEN and bulk soil ranged from 0.</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">8</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US"> to 3.</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">8</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">‰, from 1.0</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">to 4.0‰, and from 0.</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">8</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US"> to 2.</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">8</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">‰, respectively. It was clear that δ<sup>15</sup>N decreased in RS but increased in CM3 treatments. Our results </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">indicated that the amounts of h</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">ot water- and water-extracted organic matter </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">were affected by long-term </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">application of inorganic fertilizers and organic matter</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">s remarkably. However, the </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">values of δ<sup>13</sup>C for HWEOC</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US"> and </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">WEOC</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US"> were not different among 5 treatments, but </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">values</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US"> of </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">δ<sup>15</sup>N </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">of </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">HWEN and WEN </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">were affected by </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">RS </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">and </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">CM3 </span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: JA; mso-bidi-language: AR-SA;" lang="EN-US">applications clearly</span><span style="color: windowtext; line-height: 200%; font-family: 'Times New Roman','serif'; font-size: 12pt; mso-fareast-font-family: 'ＭＳ 明朝'; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">.</span>