Abstract: Application of livestock manures and plant residues is a feasible practice to largely mitigate soil-degradative trends by increasing amounts of organic matter. However, long-term effects of fertilization regimes on the distribution of organic carbon (TOC) and total nitrogen (TN) in aggregate size fractions were poorly documented in tea (Camellia sinensis (L.) Kuntze) plantations in subtropical areas. A 10-year study was thus conducted to elucidate the impacts of fertilization patterns on the stability and allocation of TOC, TN and C/N ratio within water stable aggregate (WSA) fractions in soils under non-fertilization control (CK), chemical fertilizers only (CF), and integrated use of chicken manure and legume straw with chemical fertilizers (IF), respectively. Soil (0-20 cm) samples were collected and separated into ≥2, <2-1, <1-0.5, <0.5-0.25 and <0.25-0.106βmm aggregate classes by wet sieving, and finally used for TOC and TN analysis. The results showed that the IF treatment significantly (P<0.05) increased TOC and TN storage in all aggregate fractions relative to that of CK. Irrespective of the fertilization patterns, tea soils in subtropical China stored higher amounts of TOC and TN in the ≥2βmm water-stable fraction. In terms of the TOC and TN storage, the order of different aggregate fractions in IF- and CF-treated soils was (≥2β mm ) > (<0.5-0.25βmm) > (<1-0.5βmm) > (<2-1βmm) > (<0.25-0.106βmm), whereas that of CK-treated soils was (≥2βmm) > (<1-0.5βmm) > (<0.5-0.25βmm) > (<2-1βmm) > (<0.25-0.106βmm). Furthermore, the percentage of WSA ≥2βmm ranged from 54.95% under CK to 66.97% under IF treatment. Furthermore, TOC and TN adhered to WSA ≥2βmm, which accounted for 33.31%~45.45% of TOC and 33.76%~46.60% of TN in bulk soils under all treatments. Meanwhile, the IF treatment significantly (P<0.05) increased mean weight diameter (MWD) of aggregates as compared to that in CK- and CF- treated soils. However, a lower C:N ratio was observed in different aggregate fractions in IF-treated soils compared with that of CK. Additionally, WSA ≥2βmm was positively and significantly correlated with TN and TOC contents. In conclusion, the IF treatment improved aggregate stability, increased C and N storage in bulk soil and aggregates, and thus enhanced soil quality in tea farms in subtropical China.

Key words: tea soil, fertilization practice, soil aggregate, organic carbon, total nitrogen, nutrient contributing rate