Shifting cultivation maintains but its conversion to mono-cropping decreases soil carbon and nitrogen stocks compared to
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Shifting cultivation maintains but its conversion to mono-cropping decreases soil carbon and nitrogen stocks compared to natural forest in Western Ethiopia Berhanu Terefe & Dong-Gill Kim
Received: 25 June 2018 / Accepted: 10 January 2019 # Springer Nature Switzerland AG 2019
Abstract Aims This study was conducted to assess the effects of shifting cultivation and its conversion to mono-cropping on soil organic carbon (SOC) and total nitrogen (STN). Methods We compared soil pH, texture, bulk density and SOC and STN contents and stocks (0–100 cm) in natural forest (NF), adjacent shifting cultivation (SC) areas (> 100 years old) having three (SC-3Y), five (SC5Y) and seven (SC-7Y)-year-old fallowing, and 10 year-old mono-cropping field (MCF) converted from shifting cultivation in Western Ethiopia. Results There was no significant difference in soil pH in NF and all shifting cultivation areas. However, MCF had lower soil pH compared to SC-3Y and SC-5Y. There was no or very little difference in soil texture and bulk density across the study sites. Shifting cultivation did not affect SOC and STN stocks. However, conversion of shifting cultivation to mono-cropping decreased SOC (45–50% over 10 years; loss of 11.6 ± 0.2 Mg C ha−1 yr.−1) and STN stocks (18–45% over 10 years; loss of 0.6 ± 0.1 Mg N ha−1 yr.−1). Conclusions While shifting cultivation maintained SOC and STN, its conversion to mono-cropping decreased them, potentially contributing to global warming and decreasing soil fertility.
Responsible Editor: Remi Cardinael. B. Terefe : D. 2 mm.
N z ρb n
SOC stocks (Mg ha−1) for each sampled depth were calculated using the following equation (Solomon et al. 2002) (Eq. 1):
where, C z
SOC stock (Mg ha−1) of sample depth; thickness of the sample depth (cm);
ð1Þ
STN stocks (Mg ha−1) of the sample depth; thickness of the sample depth (cm); bulk density (g cm−3) of a sample depth; and STN content (g kg−1) of a sample depth.
For soil samples collected from the NF and SC-3Y, SC-5Y and SC-7Y, SOC and STN stocks were summed up across sample depths. However, soil samples collected from MCF, SOC and STN stocks were determined differently, since soil compaction in MCF may influence the amounts of soils sampled from fixed soil depths (Solomon et al. 2002). The differences in soil bulk densities were treated by adjusting the thickness of each sampled layer in MCF with respect to equivalent mass of soils collected in NF using the following equation (Solomon et al. 2002) (Eq. 3). Zcorr¼ ρbNF =ρbMCF z
ð3Þ
where, Zcorr ρbNF ρbMCF z
Determination of soil organic carbon and nitrogen stocks
C ¼ ðz ρb cÞ 10
ð2Þ
adjusted thickness of a soil sample layer in MCF; bulk density of the sampled soil layer in NF; bulk density of the sampled soil layer in MCF; and thickness of soil layer in MCF. The adjusted thickness of soil layers was used to determine SOC and STN stocks.
Statistical analyses The normality of all data distribution was analyzed first using the Shapiro–Wilk Normality Test (Shapiro and Wilk 1965).
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