Effects of Land Use on Soil Organic C and Microbial Biomass C in Hilly Red Soil Region in Subtropical China

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1 2006,39(4): Scientia Agricultura Sinica Effects of Land Use on Soil Organic C and Microbial Biomass C in Hilly Red Soil Region in Subtropical China WANG Xiao-li 1, 2, SU Yi-rong 2, HUANG Dao-you 2, XIAO He-ai 2, WANG Li-gang 2, WU Jin-shui 2 1 College of Resources and Environment, Northwest Sci-Tech University of Agriculture and Forestry Yangling Huanjiang Experimental Station of Karst Ecosystem, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Huanjiang Abstract: Objective In order to assess the impacts of land use change on soil organic carbon (SOC) and soil microbial biomass carbon (SMBC), the contents of SOC and SMBC of surface soil samples (0 20 cm) were investigated. Method The dense sampling (the density of sampling for paddy and dry land is 3 4 per ha, for orchard is 2 3 per ha and for woodland is per ha) and the field surveys in Kenfu demonstration area of environmental immigrants of the northwest of Guangxi, a hilly landscape of red soil area of subtropical China were carried out. Result The average contents of SOC, SMBC and the ratio of SMBC and SOC were respectively (17.53±5.02) g kg -1, (278±174) mg kg -1 and (1.56±0.84)% in the area, respectively. The average contents of SOC, SMBC and the ratio of SMBC and SOC of the woodland were (17.53±5.02) g kg -1, (278±174) mg kg -1 and (1.58±0.39)%, respectively. Compared with the woodland, the contents of SOC and SMBC and the ratio of SMBC and SOC of the paddy field increased by 15.5%, 84.0% and 73.9% (P<0.01); The content of SOC of the dry land (17.50±4.89) g kg -1 decreased slightly (P>0.05) compared with the woodland, that of SMBC and SMBC/SOC decreased by 29.1% and 24.2% (P<0.01); The content of SOC, SMBC and SMBC/SOC of the orchard decreased by 26.8%, 46.1% and 26.1% compared with the woodland (P<0.01). In addition, there were significant correlations between SOC and SMBC in different land use except the paddy field. Conclusion This study indicated that the conversion of woodland into paddy field increased the accumulation of SOC and the microbial activity evidently in the hilly landscape of red soil area of subtropical China. However, the conversion of woodland into dry land or orchard reduced the content of SOC and the microbial activity to different degrees KZCX3-SW BA606A Tel: ; djjwxl@yahoo.com.cn Tel yrsu@isa.ac.cn

2 4 751 Key words: Land use; Subtropics; Hilly red soil region; Soil organic carbon; Soil microbial biomass carbon SOC C N P S [1,2] CO 2 [3] SOC SMBC 1976 Ayanaba [4] 2 Lugo [5] 10 SOC 46% 5090% Follett [6] 0 10 cm57% 52% 36% Islam [7] Dinesh [8] Powers [9] ha 0 30 cm 37% 16.5% [10~15] [10] Wang [13] 1980 [14] SOC % 26% [15] SOC 3SOC SOC SMBC SOC SMBC SOC SMBC SOC N E mm % m [16] 4.70 km /ha 2 3 /ha /ha 0 20

3 cm mm SOC [17] Vario-MAX C/N 2.0 mm -K 2 SO 4 SMBC [18] LSD - K-S SPSS SOC (17.53±5.02) g kg g kg -1 SOC (18.20±4.53) g kg -1 SOC 15.5% P<0.01 SOC SOC 26.8% P<0.01 SOC P> [19] SOC SOC SOC SOC 1 SOC 87.2% g kg % g kg g kg -1 91% 88% 99% g kg -1 σ SOC σ g kg -1 σ=2.78 g kg -1 - K-S α=0.05 P> SOC P=0.04 SOC P>0.05 SOC [20] SOC Table 1 The contents of SOC and SMBC and the ratio of SMBC and SOC under different land use K-S Items Land-use Sample Mean S.D. C.V. (%) Minimum Maximum Skewness Kurtosis P numbers SOC g kg -1 SMBC mg kg -1 / SMBC/SOC (%) Paddy field aa ** Dry land bb ** Woodland bb ** Orchard cc ** Total Paddy field aa ** Dry land cc ** Woodland bb ** Orchard dd ** Total Paddy field aa ** Dry land cc ** Woodland bb ** Orchard cc ** Total % 1%** K-S (P >0.05) Different lowercase and capital letters after the means mean respectively the differences at the 0.05 and 0.01 levels. ** means normal distribution by one-sample Kolmogorov -Smirnov test (P>0.05)

4 4 753 Table 2 The classification standards of soil organic matter in the second soil survey of China Class Level SOM (%) SOC (g kg -1 ) 1 Very high >4.0 > High Middle Little low Low Very low <0.6 <3.48 SMBC SOC SOC SMBC SMBC 3 SMBC 83.6% mg kg % mg kg mg kg -1 94% 92% 99% g kg -1 SMBC σ=218 mg kg -1 σ mg kg -1 SMBC SOC 1 SMBC Fig. 1 Histogram of SOC content Fig. 3 Histogram of SMBC content Fig. 2 Distribution of SOC under different land use SMBC 278±174 mg kg mg kg -1 1 SMBC (293±111) mg kg -1 SMBC 84.0% 29.1% 46.1% SMBC P<0.01 Fig. 4 Distribution of SMBC under different land use

5 P=0.00 P>0.05 SOC [21,22] SMBC/SOC 0.5% 4.0% SMBC/SOC 0.1 % 6.0 %(1.56±0.84)% 1 SMBC/SOC (2.75±1.28)% SMBC/SOC (1.58±0.39)% (1.20±0.42)% (1.17±0.40)% SMBC/SOC SMBC SOC SMBC SOC SMBC R 2 = n= A SOC SMBC 6-B 6-C 6-D 1996 SOC SMBC SMBC/SOC 46% 1 Fig. 5 Relation between SOC and SMBC A B C D Fig. 6 Relations between SOC and SMBC under different land use (A paddy field, B dry land, C wood land, D orchard) SOC SOC (18.20±4.53) g kg -1 SOC 15.5% P<0.01 SOC P>0.05 SOC 26.8% P<0.01 [23] SOC

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