Objective Effects of varied fertilization schemes using biochar and/or manure on soil organic carbon (SOC) at tea plantation were analyzed.

Method In a field experimentation at a tea plantation, test lots were applied continuously for 4 years with conventional chemical fertilizer (NPK), 50% chemical fertilizer replaced by manure (M50), 50% chemical fertilizer replaced by manure with 10 t·hm^–2 added biochar (M50+B10), and 50% chemical fertilizer replaced by manure with 20 t·hm^–2 added biochar (M50+B20) followed by conventional fertilization. After 2 years of the restoration of conventional fertilization management, differentiate contents and distribution of SOC fractions (Foc) in the soil under the applications of biochar and organic fertilizer separately or in combination were analyzed.

Result In comparison to NPK, M50 raised the microbial biomass carbon (MBC) in soil by 56.30% without significant effect on SOC or Foc. M50+B10 and M50+B20 increased the SOC by 28.61%-40.36%, MBC 3.43-3.71 times, particulate organic carbon (POC) 1.97-2.26 times, and mineral-bound organic carbon (MOC) by 79.18-89.43% but significantly lowered the MOC/POC ratio by 39.18-41.01%. Meanwhile, M50+B20 also significantly elevated the iron-bound organic carbon (Fe-OC) concentration by 87.76%. The sensitivity indices on the labile Foc indicated that MBC and POC were most sensitive to the different fertilization schemes.

Conclusion In two years of conventional fertilization after a 4-year combined application of biochar and organic fertilizer on a tea plantation, a residual effect of increasing SOC as well as labile and stable Foc in the soil continued. However, the organic carbon pool became less stable.