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| Effects of nitrogen deep placement on chemical properties of soil organic matter and extracellular enzyme activity in no-tillage paddy fields |
| Received:September 24, 2020 |
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| KeyWord:nitrogen deep placement;no-tillage paddy;humus;extracellular enzyme;pyrolysis-gas chromatography/mass spectrometry |
| Author Name | Affiliation | E-mail | | FAN Dai-jia | Ministry of Agriculture and Rural Affairs, Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River/College of Plant Science & Technology, Huazhong Agricultural University, Wuhan 430070, China | | | LI Cheng-fang | Ministry of Agriculture and Rural Affairs, Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River/College of Plant Science & Technology, Huazhong Agricultural University, Wuhan 430070, China
Hubei Collaborative Innovation Center for Grain Industry, Yangtze University, Jingzhou 434023, China | lichengfang@126.com | | CAO Cou-gui | Ministry of Agriculture and Rural Affairs, Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River/College of Plant Science & Technology, Huazhong Agricultural University, Wuhan 430070, China
Hubei Collaborative Innovation Center for Grain Industry, Yangtze University, Jingzhou 434023, China | ccgui@mail.hzau.edu.cn |
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| Abstract: |
| This study investigated the impacts of N deep placement on the chemical properties of soil organic matter(SOM) and soil enzyme activity in no-tillage(NT) paddy soil. Multiple cropping of rice and rapeseed was carried out under NT in the experimental site located in Huaqiao County, Wuxue City, Hubei Province from 2015 to 2016. The growing seasons of rice and rapeseed were from June to October and from October to May of the next year, respectively. Five fertilizing treatments, including no N fertilizer(CK), N surface broadcasting(SB), and N deep placement at soil depths of 5 cm, 10 cm(10D), and 20 cm were applied with three replicates per treatment. The soil organic carbon(SOC) contents of different SOM fractions, the chemical compositions and properties of humic acid(HA) and light fraction organic matter(LFOM), and the activities of different soil enzymes were determined. Redundancy analysis was carried out to reveal the relationships between the chemical properties of SOM and enzyme activity. The results showed that compared with SB, N deep placement significantly increased the SOC contents in the HA and LFOM by approximately 10.5%~30.7% and 31.7%~53.5%, respectively. The hydrophobicity of HA under N deep placement was 1.3%~11.6% higher than that under SB. Moreover, N deep placement significantly improved the contents of polysaccharides and lipids in the LFOM by 9.0%~24.1% and 43.4%~68.3%, respectively. Compared with those under SB, N deep placement significantly inhibited the activities of β-glucosidase(BG) and β-N-acetylglucosaminidase(NAG) by 22.2%~48.9% and 32.7%~40.4%, respectively, whereas it significantly stimulated the activities of L-leucine aminopeptidase(LLA) and phenol oxidase(PHO) by 37.1%~38.5% and 11.0%~16.0%, respectively. In addition, the redundancy analysis showed that the contents and hydrophobicity of HA and the contents of polysaccharides and lipids in the LFOM were positively correlated with the LLA and PHO activities and negatively correlated with the BG and NAG activities. The results demonstrated that the chemical compositions and properties of humus and LFOM were regulated by the soil enzyme activity. Nitrogen deep placement decreased the humus aromaticity by stimulating the PHO activity and increased the polysaccharide contents in the LFOM by inhibiting the BG and NAG activities. Moreover, compared with those under SB, N deep placement, especially 10D, increased the SOC contents in the HA and LFOM mainly by activating the growth of crops and microbial communities, and altered their chemical properties and compositions mainly through regulating the activities of BG, NAG, and PHO, thereby promoting the soil fertility and quality. Therefore, it is worthwhile to further advocate for and improve the application of 10D placement in NT paddy fields. |
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