Short-term Responses to a Single Tillage Event
Francisco Calderón, Louise Jackson, Kate Scow, Dennis Rolston

The short-term responses of soil microbial processes and community structure to perturbation constitute one aspect of soil quality. Such responses are often associated with an increase in the emissions of greenhouse gases (i.e., CO2, NO, or N2O) and the accumulation and potential loss of nitrate by leaching.

We conducted a series of experiments on responses of soil carbon and nitrogen dynamics, microbial biomass, and microbial community structure to a tillage event in intensively managed vegetable crop systems in California (Calderon et al., 2000, Soil Biology and Biochemistry; Calderon et al., 2001, Soil Science Society of America J.; Calderon and Jackson, 2002, J. Environmental Quality). Our results indicate:

CO2 emission from the soil surface is high for the first day after tillage, but respiration declines or remains constant, suggesting that physical processes are responsible for the high flux from the soil surface.

  • Net N mineralization and nitrate accumulation increase for several days after tillage, and this can be accompanied by higher denitrification rates. Tillage causes immediate changes in microbial community structure, based on phospholipid fatty acid (PLFA) analysis, and in PLFA 'stress' markers, but little concomitant change occurs in total microbial biomass.
  • These short-term responses indicate that tillage does stimulate immediate C mineralization by microbes in these intensively managed soils, and suggest that longer-term loss of SOM in tilled soils may be due to changes in soil physical properties that cause environmental conditions conducive to higher respiration and decomposition rates.


Based on this research, tillage events contribute to decreased soil quality by increasing emissions of greenhouse gases, and increasing the potential for nitrate leaching to groundwater, and these negative aspects must be weighed against benefits of tillage for increasing the health and productivity of some crops.

 References 

Calderón, F.J., L.E. Jackson, K.M. Scow, and D.E. Rolston. 2000. Microbial responses to simulated tillage in cultivated and uncultivated soils. Soil Biology and Biochemistry 32: 1547-1559.
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Calderón, F.J., L.E. Jackson, K.M. Scow, and D.E. Rolston. 2001. Short-term dynamics of nitrogen, microbial activity, and phospholipid fatty acids after tillage. Soil Science Society of America Journal 65:118-126.
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Calderón, F.J. and L.E. Jackson. 2002. Roto-tillage, disking and subsequent irrigation: effects on soil nitrogen dynamics, microbial biomass and carbon dioxide efflux. Journal of Environmental Quality 31:752-758.
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