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

Table 2

Effect of different treatments of corn straw on humic substances in black soil.

Depth (cm)	Treatment	HA-C	FA-C	HM-C	PQ (%)
0∼20	CK	3.19 ± 0.10^d	1.89 ± 0.10^b	5.31 ± 0.16^c	62.78 ± 0.01^b
	SCR	4.24 ± 0.80^a	2.22 ± 0.08^a	6.49 ± 0.46^a	65.67 ± 0.01^a
	MBR	3.96 ± 0.18^b	2.20 ± 0.13^a	6.16 ± 0.12^ab	64.25 ± 0.02^a
	SEDI	3.68 ± 0.12^c	2.08 ± 0.14^a	5.85 ± 0.25^b	63.85 ± 0.02^a
20∼40	CK	3.00 ± 0.16^c	1.78 ± 0.15^a	5.05 ± 0.13^c	62.71 ± 0.03^a
	SCR	3.22 ± 0.22^bc	1.86 ± 0.20^a	5.80 ± 0.19^b	63.41 ± 0.04^a
	MBR	3.60 ± 0.10^b	2.03 ± 0.20^a	6.01 ± 0.21^b	63.90 ± 0.04^a
	SEDI	4.03 ± 0.14^a	2.13 ± 0.20^a	6.64 ± 0.38^a	65.39 ± 0.03^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 ().