Effects of organic materials on soil organic carbon and fractions of active carbon in soda saline soil

Objectives We compared the effects of four kinds of organic materials on increment of soil organic carbon quality and quantity, and studied the correlation between soil organic carbon and active carbon fractions and main salinity and alkali indexes in the soda saline soil of Datong basin,northern Shanxi Province, to provide a reference for the biological remediation of the soils.

Methods The field experiment was conducted in Huairen County of northern Shanxi from 2016 to 2017. The tested organic materials included weathered coal, biochar, cattle manure and corn stalk, all the organic materials were applied at rate of 9000 kg/hm² organic carbon annually, and no organic material addition was served as control (CK). The spring maize yield was investigated, the content of soil organic carbon (SOC), water-soluble organic carbon (WSOC), easily oxidizable organic carbon (EOC) and light fraction organic carbon (LFOC) were measured.

Results Compared with CK, addition of biochar and corn stalk did not increase the maize yield significantly, while weathered coal and cattle manure treatments markedly increased the yield by 30.2% and 30.3%, respectively. All organic material addition enhanced the SOC accumulation in 0–20 cm soil layer, and weathered coal and cattle manure increased 47.6% and 36.1%, respectively, which were significantly higher than those of corn stalk and biochar. Similarly, all organic material addition significantly increased the contents of WSOC, EOC and LFOC in 0–20 cm soil layers. WSOC and EOC contents in weathered coal, cattle manure treatments were significantly higher than those in biochar and corn stalk treatments. Addition of biochar had the lowest LFOC content. The WSOC/SOC in cattle manure treatment was significantly higher than CK in 0–20 cm layer, while those in the four organic material treatments were not significantly different. The EOC/SOC in cattle manure treatment was highest, followed by weathered coal, both were significantly higher than CK. The LFOC/SOC appeared in a descending order as corn stalk, cattle manure > weathered coal, biochar > CK. Organic material addition also resulted in a decrease of soil pH, electrical conductivity (EC) and exchange sodium percentage (ESP) in 0–20 cm soil layer, and such decrease effects in weathered coal and cattle manure treatments were stronger. SOC and fractions of soil active carbon were negatively correlated with soil pH, EC and ESP.

Conclusions Addition of cattle manure and weathered coal could markedly increase SOC quality and quantity, reduce soil pH, EC and ESP, and further increase maize yield, so are thought to be suitable amendment materials for soda saline soil of northern Shanxi.