Wednesday, June 28, 2017

Low Disturbance vs High Disturbance DS drills

     All DS drills can seed and grow an excellent crop and improve soil health.  Farming too efficiently use the moisture we are provided, and the pace too improving soil health is the difference I see between high and low disturbance drill designs.
   High disturbance drills (the term I use for all hoe, double disc, and some single disc openers) all share a similar problem, --they move or disrupt too much soil which exposes the soil surface.  As a result they break infiltration channels, they accelerate decomposition of cover, they plant unwanted seed, and they damage the soil food web if any is present.  There are places in our field where even the CrossSlot fits into the high disturbance category, --on steep slopes where side pressure causes a wider slot, and where we turn.
     I distinguish between DS drills by the amount of soil surface they disturb.  They range from disrupting nearly the entire surface down to a narrow slot of <1.5 inches.  I would say that most hoe drills fall in the high disturbance category, and most single disc drills would fall in the low disturbance category and the CrossSlot in the ultra-low disturbance category.  Others may have their own scale.  By the numbers:
      High disturbance drills:  Their configuration disrupts a large percentage (>70%) of the soil surface and most or all of the surface residue. 
      Low disturbance drills:  Their configuration disrupts (<30%) of the soil surface and about 60% of the residue.
      Ultra-low disturbance drills:  Their configuration disrupts (<15%) of the soil surface and maybe 40% of the residue.
      Whether the numbers accurately describe the drill type performance is not the point here.  What is important is that they represent the concept that the more soil and residue that is disturbed, the more moisture you lose from evaporation, the less moisture your field can absorb from later rains because of disrupted channels, the more biological communities in the soil you disrupt which effects plant food production,  and the more unwanted seed that will be  planted grow and compete with the crop.
      To maximize moisture retention and absorption, you will want to minimize disturbance of the soil surface, grow and maintain the maximum amount of residue possible, and leave it as tall as possible in the absence of a growing crop. (see other posts for the reasoning behind this statement).  It's my belief as well that this statement is valid for all rainfall regions whether 7" or 70".


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