Biochar amendment promotes limited organic carbon increase in
saline-sodic soil of the Songnen Plain, Northeast China
Abstract
To what extend that biochar addition promotes organic carbon increase in
saline-sodic soils, however, remains poorly understood. Here, we
evaluated soil organic carbon (SOC) contents change before and after
biochar addition, and deciphered which driving factor or process govern
SOC change with biochar application. There was a limited increase in
SOC, about by +1.16%~+12.8%, even biochar was applied
at the rate of 10% of bulk soil weight. However, soil dissolved organic
carbon (DOC) increased significantly by up to 67%. About half SOC was
stored in small macroaggregates (250-2000 μm, CPOC), and SOC in silt and
clay-sized particles (<53 μm) decreased obviously with biochar
addition. Microorganism biomass, represented by phospholipid fatty acid,
increased with biochar amendment, of which actinomycetes, fungi,
protozoon, and bacteria with straight-chain saturated fatty acids (OB)
increased remarkably. DOC was governed by ACT and soil N:P ratio, while
SOC mostly depended on CPOC. Biochar addition aggravated nitrogen
limitation in saline-sodic soils, and the roles of microorganisms on
regulating SOC greatly depended on nitrogen bioavailability. Biochar
amendment had greatly changed interactions between environmental factors
and SOC in saline-sodic soils. The effects of nutrients on soil carbon
changed to strongly negative from strongly positive after and before
biochar addition, meanwhile, aggregation was the only factor with
positive effects on soil carbon change. How to mitigate nutrient
limitation and improve soil aggregation process should be considered in
priority when biochar was used to increase SOC in saline-sodic soils.