Fluorescence Spectroscopy and ¹³C NMR Spectroscopy Characteristics of HA in Black Soil at Different Corn Straw Returning Modes

Table 3

Effect of straw returning to the field on HA element composition in soil.

Depth (cm)	Treatment	Element content (g·kg^−1)				O/C	H/C
		C	H	N	O
0∼20	CK	487.3 ± 0.8^d	44.99 ± 0.30^d	22.71 ± 0.28^d	477.0 ± 0.8^a	0.734 ± 0.002^a	1.108 ± 0.009^c
	SCR	512.9 ± 0.7^a	49.54 ± 0.06^a	27.88 ± 0.10^a	422.5 ± 0.5^d	0.618 ± 0.001^d	1.159 ± 0.001^b
	MBR	495.1 ± 0.9^b	47.97 ± 0.10^b	25.70 ± 0.12^b	435.2 ± 0.9^c	0646 ± 0.001^c	1.140 ± 0.002^a
	SEDI	491.9 ± 0.8^c	46.43 ± 0.08c	23.42 ± 0.09^c	467.5 ± 0.4^b	0.713 ± 0001^b	1.133 ± 0.002^a
20∼40	CK	482.1 ± 0.9^d	43.21 ± 0.90^d	21.52 ± 0.10^c	479.0 ± 0.9^a	0.745 ± 0.001^a	1.076 ± 0.024^c
	SCR	486.8 ± 0.5^c	44.56 ± 0.08^c	22.90 ± 0.66^b	475.0 ± 0.7^b	0.732 ± 0.002^b	1.099 ± 0.001^bc
	MBR	488.7 ± 0.6^b	45.5 ± 0.17^b	23.20 ± 0.44^b	453.1 ± 0.9^c	0.695 ± 0.001^c	1.117 ± 0.005^b
	SEDI	501.2 ± 0.7^a	48.04 ± 0.16^a	25.12 ± 0.09^a	429.2 ± 0.8^d	0.642 ± 0.001^d	1.150 ± 0.002^a

Note. CK: no straw application; SCR: straw mulching; MBR: straw deep ploughing; SEDI: straw enrichment and deep incorporation. There were significant differences between different letters representing different treatments ().