How do I reflect carbon sequestration in a farming system that uses different tillage for different crops within a rotation?

Michaela

The IPCC defines tillage categories as below. As there are many tillage options available to farmers, anything which isn’t clearly at one end or the other can get classified as “reduced till.”

When you consider ticking the box for tilling under the “carbon” tab in the CFT, think of “no-till”, “reduced-till”, and “conventional till” as terms that apply to a rotation rather than to crops in a rotation. “No-till” means the land is never tilled, “conventional till” means annual or more than annual tillage, “reduced-till” is anything in between.

Although the tool can be used in many ways to try to predict subtle effects of annual difference in management, these give the illusion of a precision the tool really doesn’t have. The effects of soil management changes on soil carbon are highly unpredictable in the 3-5 years after a practice change. Farmers should tick the box on tillage changes only if/when they are confident that the transition to a different tillage system is of longer term (>5 years).

If on a growing area farmers manage crops in rotation with different tilling practices, they should always choose the most conservative option, e.g. if the management switches between no-till & reduced till, choose reduced till for any crop in the rotation.

Conventional tillage: Substantial soil disturbance with full inversion and/or frequent (within year) tillage operations. At planting time, little (e.g., <30%) of the surface is covered by residues.
 
Reduced tillage: Primary and/or secondary tillage but with reduced soil disturbance (usually shallow and without full soil inversion). Normally leaves surface with >30% coverage by residues at planting.
 
No-till: Direct seeding without primary tillage, with only minimal soil disturbance in the seeding zone. Herbicides are typically used for weed control.

Some examples:

  • (a) The farmer does not own the field, they cannot make long term decisions for tillage on that field.  If the field is not owned or if the farmer is not confident about their tillage plans in the future, assume that the tillage system they have used in the recent past will continue and assign the tillage class as the most intensive tillage system used in the cropping rotation during the past 4 years.
  • (b) If the field is owned by the farmer, if possible, add a question for the Specialist to ask the farmer about his/her tillage plans specific to the field, moving forward.  The farmer can select from among our current tillage classes.
    • In the case where the farmer anticipates applying different tillage options to different crops (e.g. no-till for soy and 1-pass for corn) select the most intensive tillage class to apply to the field in the CFT.
    • If the farmer does not know what he/she plans for tillage or isn’t decided, use the previous data and select the most intensive tillage class that they have historically used.