Tillage Intensity

This is the variable for which much discussion has occurred. With recognition to Heather McNairn (AAFC) and Andy Davidson (AAFC), Alyssa Whitcraft (NASA Harvest) has summarized their discussions below:

Although we have identified several biophysical characteristics that can be identified with satellite data, and that can indicate a tillage event and can be used to approximate intensity, without contextual information it is difficult to definitively determine the very relevant nature of the event which has left these biophysical characteristics:

1. Crop Residue Cover Percentage (this is an EAV)
   1. Some efforts to map tillage utilize thresholds for defining qualitative classes such as, “no-till”, “conservation tillage”, “reduced tillage”, and “conventional tillage.”
      1. However, residue remains in vastly different quantities and functionalities after harvest, and is determined by, for example: prior crop, type of harvesting, and purpose of harvesting (e.g. animal feed vs. commodity grain).
      2. The function of that residue in terms of soil protection is contingent upon the size of the remaining vegetation pieces.
      3. Further, the class categories and definitions are highly specific to the policy in place as well as the characteristics of the landscape.
   2. The relevance of residue to tillage identification is related to both the absolute residue cover that remains, as well as residue change (which requires a time series analysis).
2. Soil Disturbance
   1. Whether or not soil has been disturbed, and to what degree, will have the largest impact on nutrient cycling, ecosystem exchange (GHG emissions, soil organic carbon stocks), water infiltration capability, and water quality.
   2. At present, remote sensing based methods to identify and estimate soil disturbance are in development, but not yet mature enough to warrant an EAV.
   3. The relative import of soil disturbance (both occurrence and measurement of degree) is only determined in combination with other environmental variables (e.g. precipitation, wind speed) as well as site descriptions (e.g. topography, soil type, soil condition before tillage), not all of which are currently articulated as EAVs.
3. Vegetation Fractional Cover (this is an EAV)
   1. As noted above, the protection of soil from water and wind erosion is related to the amount of total coverage of the soil. Both living, green, photosynthetic vegetation and non-photosynthetic residue comprise Vegetation Fractional Cover. The relative value of these constituent parts to soil protection is beyond the scope of GEOGLAM’s work.

In addition to these biophysical characteristics, the reason for wanting to measure and monitor tillage will have a large bearing on the definition used and the necessary covariates measured with it. Put simply, monitoring tillage to verify compliance with a policy that says, “you cannot till” will look very different than monitoring tillage to estimate the impacts of tillage on soil erosion or carbon emissions/sequestration.