Use of soil enzyme activity as possible measures of carbon sequestration under different tillage and cropping practices

Background/Question/Methods Land use patterns affect biological and physical processes in the soil. These in turn can affect processes in soils which may influence carbon sequestration. Understanding the effects of various land uses on soil functions is important in protecting soils from degradation and ultimate contribution of soil carbon to global CO₂ fluxes.  Current measurement of effect of landuse and other environmental pertuberances on carbon sequestered or lost from soils have been monitored primarily by measuring soil organic carbon. Recent evidence that certain soil enzyme activities may have high correlation with soil organic matter make soils enzymes a possible way of following impacts of land practices on carbon sequestration. The overall goal of this project was to evaluate the phosphatases as possible measures soil organic carbon under two tillage systems, Conventional (CT) and No- or Minimum- tillage systems (NT). The enzyme activities analyzed were phosphomonoesterase (acid and alkaline) and phosphodiesterase. The levels of soil enzymes and organic carbon in the two tillage systems were monitored in two soils in OK and AL. Soil enzyme activity and organic carbon were determined using standard methods.

Results/Conclusions Land use did significantly affect enzyme activities and organic matter content in the soils studied.  Conventional tillage practices resulted in significant (p<0.05) lowering of organic carbon compared with No-till or minimum tillage practices. The results showed that the percent organic carbon was significantly higher (p<0.01) in the NT plots compared to the CT plots as well as in the 0-5 cm soil depth compared to the 5-15 cm soil depth. Enzyme activities were significantly (p<0.05) higher in NT compared to CT with acid phosphomonoesterase levels revealing significantly higher (p<0.05) levels at 5-15 cm depths in the NT plots compared to similar depth in the CT.  Soil under native grass which received minimum tillage generally had significantly (p<0.05) lower phosphatase activity then soil which received conventional tillage. Soil organic carbon content was significantly (p< 0.05) correlated with the activities of all the phosphatases studied. The high correlation between the phosphatses and organic carbon in the two soil types and tillage systems studied suggests that soil phophatase activities may be a possible candidate for following changes in carbon in soils.