Carbon Sequestration: The Lack of Initial Measurement Could Bias Interpretations of Management Effect on Soil Carbon.

Much research has been done in the last decades to determine the effect of management practices on the rate of soil carbon (C) sequestration over time .Generally paired fields are sampled and soil organic carbon (SOC) content in soils under each management system is determined. Conclusions about the effectiveness of any different management systems in sequestering soil C are established based on the SOC difference and length of the experiment. However, properly archived historic samples are often unavailable. In this study, a split plot experiment was established in 1997 at Mead, NE with crop rotation as the main factor – continuous maize (CC) and maize/soybean (CB) – and nitrogen applied to maize as the sub factor – 0 kg/ha (0N), 100 kg/ha (100N), 300 kg/ha (300N). Soil samples were taken to a depth of 120 cm in 1998 and in 2009 and SOC was determined. Two analyses were conducted; one based solely on treatment differences among samples obtained in 2009 A second analysis was made based on SOC trend over time using samples from 1998 as a benchmark. Results obtained from analyzing only 2009 samples show greater carbon content under CB rotation than under CC when the whole soil profile was considered. When carbon trends were analyzed over time, less SOC is lost under CC than CB. These findings suggest that conclusions based solely on one sampling date in paired experiments do not account for possible initial differences. Analyzing trend of carbon change over time allow a better understanding of the effect of management practices on SOC over time.