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a Div. of Soil Science and Agricultural Chemistry, Indian Agricultural Research Institute, New Delhi 110012, India
b USDA-ARS Pacific West Area Land Management and Water Conservation Research Unit, Pullman, WA 99164-6421
* Corresponding author (tapanjp{at}iari.res.in).
Comparative assessments for evaluating soil organic C (SOC) and its characteristics were made at different soil (Palouse silt loam) depths (0–5, 5–10, 10–20, and 0–20 cm) among sites with seven contrasting management histories: conventional inversion tillage (CT) followed by no-till (NT) for 4 (NT4) and 28 (NT28) yr; bluegrass (Poa pratensis L.) seed production for 9 yr followed by NT for 4 yr (BGNT4); a sequence of 10 yr NT, 3 yr CT, and 1 yr NT (NTR); CT followed by 11 yr perennial grass under the Conservation Reserve Program (CRP); long-term >100 yr CT; and native prairie (NP). Overall ranking of SOC, particlulate organic C (POC), and microbial biomass C (MBC) at 0 to 20 cm was NP > NTR > NT4 = NT28 > CRP > BGNT4 = CT. Greater SOC, POC, and MBC in NTR than NT28 indicated that tillage rotation could result in more soil C sequestration, primarily by increasing C stocks in 5- to 20-cm depths. The POC was labile in nature as it highly correlated with Cmin (r = 0.69, P < 0.01) and MBC (r = 0.86, P < 0.01) as well as SOC (r = 0.89, P < 0.01). We concluded that: (i) neither NT nor conversion to perennial vegetation would attain the SOC found in NP over 10 to 30 yr; and (ii) medium duration of NT (10 yr) combined with short intervals of CT (3 yr) followed by NT might increase SOC compared with continuous long-term NT under annual cropping.
Abbreviations: BGNT, bluegrass seed followed by no-till Cmin, carbon mineralization CRP, Conservation Reserve Program CT, conventional tillage MBC, microbial biomass carbon MQ, microbial quotient NP, native prairie NT, no-till NTR, no-till reestablished, POC, particulate organic carbon qCO2, microbial metabolic quotient SOC, soil organic carbon
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