Effects of biochar on organic carbon content and fractions of gray desert soil

Soil organic carbon is critical for soil fertility and crop yield. Biochar (BC) is a carbon-rich organic material derived from incomplete pyrolysis of biomass and can constitute a significant fraction of soil carbon due to its prolonged lifespan in soils. The study investigated the influence of biochar on wheat growth and soil organic carbon in grey desert soils under greenhouse experiment. The objective was to learn how this soil amendment improved crop growth and increased soil carbon storage. Biochar was produced from dried cotton stalks via pyrolysis in oxygen-limited conditions. Three qualities of biochar produced at 450 ℃, 600 ℃ and 750 ℃ (referred as BC450, BC600 and BC750) were used as the soil organic amendment in the study. The experiment was that of 3×3 factorial design with three qualities of biochar (BC450, BC600 and BC750) and three application rates (5 g·kg^-1, 10 g·kg^-1 and 20 g·kg^-1 of soil weight) plus an un-amended soil set as the control (CK). Wheat was planted for two consecutive growth seasons in 2009. The first-season of wheat was May 8 to July 15 and the second was August 8 to October 15. The results showed that dry matter weight of wheat under added BC treatments were significantly higher than that under CK. There were no significant differences among the three types and three application rates of biochar in terms of the first-season wheat dry matter weight. However, the second-season wheat dry matter weight was significantly affected by biochar qualities, application rates and the interaction of them. The highest wheat dry matter weight was under BC750 with an application rate of 20 g·kg^-1. Soil total organic carbon increased with increasing biochar pyrolysis temperature and application rate. Soil total organic carbon under BC450, BC600 and BC750 was 2.11, 3.32 and 4.19 times of CK, respectively. Soil readily oxidizable carbon content was significantly higher under biochar treatments than the control. Water-soluble organic carbon was significantly higher under biochar treatments at 5 g·kg^-1 and 10 g·kg^-1 application rates than the control. However, there was no significant difference between 20 g·kg^-1 biochar treatment and the control. Microbial biomass carbon increased significantly under biochar treatment, except for BC750 biochar at 5 g·kg^-1 application rate. Readily oxidizable carbon and microbial biomass carbon contents of soil changed in the following order of BC450 > BC600 > BC750. However, soil water-soluble organic carbon content was not affected by biochar pyrolysis temperature. The order of influence of different biochar application rates on readily oxidizable soil carbon was 10 g·kg^-1≈20 g·kg^-1 > 5 g·kg^-1, and that of water-soluble organic carbon was 5 g·kg^-1≈10 g·kg^-1 > 20g·kg^-1. For soil microbial quotient, BC450 and BC600 at 5 g·kg^-1 application rate were higher than CK. Also BC450 at 10 g·kg^-1 and 20 g·kg^-1 application rates were not significantly different from CK. Other biochar treatments were as well lower than CK. These results suggested that application of biochar as soil organic amendment was an efficient way of increasing soil carbon reserve, changing soil organic carbon fraction and promoting soil productivity.