Evaluating the Effect of Tillage on Carbon Sequestration Using the Minimum Detectable Difference Con

Three long-term field trials in humid regions of Canada and the USA were used to evaluate the influence of soil depth and sample numbers on soil organic carbon (SOC) sequestration in no-tillage (NT) and moldboard plow (MP) corn (Zea mays L.) and soybean (Glycine max L.) production systems. The first trial was conducted on a Maryhill silt loam (Typic Hapludalf) at Elora, Ontario, Canada, the second on a Brookston clay loam (Typic Argiaquoll) at Woodslee, Ontario,Canada, and the third on a Thorp silt loam (Argiaquic Argialboll) at Urbana, Illinois, USA. No-tillage led to significantly higher SOC concentrations in the top 5 cm compared to MP at all 3 sites. However, NT resulted in significantly lower SOC in sub-surface soils as compared to MP at Woodslee (10-20 cm, P = 0.01) and Urbana (20-30 cm, P < 0.10).no-tillage="" had="" significantly="" more="" soc="" storage="" than="" mp="" at="" the="" elora="" site="" (3.3="" mg="" c="" ha-1)="" and="" at="" the="" woodslee="" site="" (6.2mg="" c="" ha-1)="" on="" an="" equivalent="" mass="" basis="" (1350="" mg="" ha-1="" soil="" equivalent="" mass).="" similarly,="" nt="" had="" greater="" soc="" storage="" than="" mp="" at="" the="" urbana="" site="" (2.7="" mg="" c="" ha-1)="" on="" an="" cquivalent="" mass="" basis="" of="" 675="" mg="" ha-1="" soil.="" however,="" these="" differences="" disappcared="" when="" the="" entire="" plow="" layer="" was="" evaluated="" for="" both="" the="" woodslee="" and="" urbana="" sites="" as="" a="" result="" of="" the="" higher="" soc="" concentrations="" in="" mp="" than="" in="" nt="" at="" depth.="" using="" the="" minimum="" detectable="" difference="" technique,="" we="" observed="" that="" up="" to="" 1500="" soil="" sample="" per="" tillage="" treatment="" comparison="" will="" have="" to="" be="" collected="" and="" analyzed="" for="" the="" elora="" and="" woodslee="" sites="" and="" over="" 40="" soil="" samples="" per="" tillage="" treatment="" comparison="" for="" the="" urbana="" to="" statistically="" separate="" significant="" differences="" in="" the="" soc="" contents="" of="" sub-plow="" depth="" soils.="" therefore,="" it="" is="" impracticable,="" and="" at="" the="" least="" prohibitively="" expensive,="" to="" detect="" tillage-induced="" differences="" in="" soil="" c="" beyond="" the="" plow="" layer="" in="" various="" soils.="">