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Poor soil has restricted the crop production in semiarid soil. Fulvic acid (FA) is considered to play an significant role in soil fertility. The amount and structure of FA after application of different organic wastes (OWs) was assessed in this work. Six treatments were involved in this experiment: chemical fertilizer combined with chicken manure (CM), sheep manure (SM), maize straw (MS), fodder grass (FG), and tree leaves (TL), while chemical fertilizer only was used as control (CK). The soil FA content (P < 0.05) after the application of TL was the highest than other OWs. The E 4 /E 6 ratios, Δlog K values, aliphatic C/aromatic C ratios of soil FA after the application of TL were the lowest than other OWs, whereas the C/H ratio was the highest. The specific fluorescence intensities (SFI) of peak A (Ex/Em 260–265/415-430 nm) and peak B (Ex/Em 310–315/415-430 nm) from EEM fluorescence spectrum of FA were the lowest after the application of TL. In conclusion, the application of TL was the most effective for improving FA accumulation, and making FA complex and stability. Thus, TL is the recommended OW for use in semiarid soil under plastic mulched drip irrigation conditions. The soil FA content after application of TL was the highest. • The application of TL could make the structure of FA complex and stability, and improve storage of soil organic matter. • The application of CM could make the structure of FA simple and improve the updating of FA. • TL would be used as the most suitable OW type in semiarid soil under plastic mulched drip irrigation conditions. [ABSTRACT FROM AUTHOR]

The objective of this work was to evaluate the variation in the amount and structure of humic acid (HA) after the application of organic wastes (OWs) in semiarid soil under plastic mulched drip irrigation, measured by elemental composition, excitation-emission matrix (EEM) fluorescence, and carbon 13 nuclear magnetic resonance ( 13 C CPMAS NMR). The experiment involved chemical fertilizer combined with chicken manure (CM), sheep manure (SM), maize straw (MS), fodder grass (FG), and tree leaves (TL), while chemical fertilizer only was used as control (CK). The highest cation exchange capacity (CEC), soil organic carbon (SOC), and HA contents ( P < 0.05) were achieved for TL compared to other OWs. The E 4 /E 6 ratio, Δlog K value, and the aliphatic C/aromatic C ratio of HA were the lowest for TL treatment than for other OW treatments, whereas the highest C/H ratio was obtained. The specific fluorescence intensities (SFI) of peak A (330–370/460-490 nm), peak B (450–465/515-525 nm), and peak C (255–270/465-490 nm) mainly referred to humic acid component from EEM fluorescence spectrum of HA were lower for TL compared to other OWs. In conclusion, the application of TL was the most effective for improving the accumulation of SOC and HA, and making the structure of HA complex and stability. Thus, TL is the recommended OW for use in semiarid soil under plastic mulched drip irrigation conditions. [ABSTRACT FROM AUTHOR]