Abstract
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. The ratio of soil to extracted water was 2:3. The amounts of hot water-extracted organic carbon and nitrogen (HWEOC and HWEN) at 80 o C and 16 hours, water-extracted organic carbon and nitrogen (WEOC and WEN) at room temperature, and their δ 13 C and δ 15 N were measured from the five fertilizer treatment plots as [1) PK, 2) NPK, 3) NPK + 6 Mg ha -1 rice straw (RS), 4) NPK + 10 Mg ha -1 rice straw compost (CM1), and 5) NPK + 30 Mg ha -1 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 1 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 among all treatments . The values of δ 13 C for HWEOC and WEOC ranged from -28.2 to -26. 5 ‰ and from -28.3 to -27.0‰, similar to the original rice straw and rice straw compost , and lower than the value of original soil at -22.5 ‰. The values of δ 15 N of HWEN, WEN and bulk soil ranged from 0. 8 to 3. 8 ‰, from 1.0 to 4.0‰, and from 0. 8 to 2. 8 ‰, respectively. It was clear that δ 15 N decreased in RS but increased in CM3 treatments. Our results indicated that the amounts of h ot water- and water-extracted organic matter were affected by long-term application of inorganic fertilizers and organic matter s remarkably. However, the values of δ 13 C for HWEOC and WEOC were not different among 5 treatments, but values of δ 15 N of HWEN and WEN were affected by RS and CM3 applications clearly .
Highlights
Long-term experiments (LTE) started more than one hundred years ago, with the first LTE initiated in 1843 at Rothamsted Experimental Station in England
Many LTEs researches on C and N dynamics focused on water-extracted organic carbon (WEOC) and waterextracted N (WEN), there is no report on the combination of soil WEOC and WEN with their natural stable isotopes, δ 13C and δ 15N
We evaluated the effects of long-term application of mineral fertilizers and/or organic matters on amounts of their stable isotopes of hot water- and water-extracted carbon and nitrogen of the soil samples collected from a single rice paddy in Yamagata, northeastern Japan
Summary
Long-term experiments (LTE) started more than one hundred years ago, with the first LTE initiated in 1843 at Rothamsted Experimental Station in England. The initial purpose of these LTEs was to understand the change in agrosystems productivity, it broadened over time to assess other impacts such as ecosystem perturbations, global environmental changes on agrosystems sustainability (Rasmussen et al, 1998; Körschens, 2006). Natural stable isotopes of C and N (δ13C and δ15N) are widely used to study the dynamic of soil organic matter (SOM). Among the different fractions of SOM, water-extracted organic matter (WEOM) represents a small fraction, involved in many soil processes (Chantigny, 2003; Guigue et al, 2014). WEOM has been widely used to extract in both moist soil and dry soil, since both water extracts of moist and air-dried soils are simple to obtain and can provide a labile organic matter. Many LTEs researches on C and N dynamics focused on WEOC and waterextracted N (WEN), there is no report on the combination of soil WEOC and WEN with their natural stable isotopes, δ 13C and δ 15N
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