The impact of the long-term application of mineral nitrogen and sewage sludge fertilizers on the quality of soil organic matter

Chemical and Biological Technologies in Agriculture

Table 3 Qualitative and quantitative soil organic matter (SOM) parameters

Parameter	Con	N120	N240	S120	S240
C_{SOM (%)}	1.62^a	1.61^a	1.61^a	1.75^a	1.84^a
C_HWE (mg kg⁻¹)	196^cd	165^ab	148^a	172^bc	189^c
C_DOC (mg kg⁻¹)	26.4^c	21.1^b	15.4^a	22.4^b	29.7^d
C_HA (%)	0.244^c	0.162^a	0.185^ab	0.182^ab	0.222^bc
C_FA (%)	0.182^a	0.173^a	0.195^a	0.165^a	0.189^a
C_HS (%)	0.487^a	0.486^a	0.529^a	0.450^a	0.544^a
C_HA/FA	1.352^b	0.950^a	0.948^a	1.102^a	1.215^ab
N_t (%)	0.144^a	0.138^a	0.148^a	0.155^a	0.162^a
C_SOM/N_t	11.2^a	11.6^a	10.9^a	11.3^a	11.4^a
PWI	0.029^b	0.021^ab	0.020^a	0.021^ab	0.023^ab
WSA	0.509^b	0.397^a	0.387^a	0.426^ab	0.418^ab
EEG (mg kg⁻¹)	983^ab	952^a	999^ab	971^ab	1052^b
TG (mg kg⁻¹)	2091^a	2027^a	2013^a	2126^a	2145^a

Different superscript letters describe statistically significant differences between treatments. Tukey HSD test; p < 0.05
Con Unfertilized control; N120 Mineral fertilization (120 kg N ha⁻¹); N240 Mineral fertilization (240 kg N ha⁻¹); S120 Sewage sludge (120 kg N ha⁻¹); S240 Sewage sludge (240 kg N ha⁻¹). C_SOM Soil organic matter carbon; C_HWE Mineralizable soil organic carbon; C_DOC Dissolved organic carbon; C_HA Carbon of humic acids; C_FA Carbon of fulvic acids; C_HS Carbon of humic substances; C_HA/FA Carbon in humic and fulvic acid ratio; N_t Total nitrogen content; C_SOM/N_t Soil organic matter carbon/total nitrogen ratio; PWI Potential wettability index; WSA Aggregate stability index; EEG Easily extractable glomalin; TG Total glomalin