While soils are made up of solid materials (sand, silt, clay and organic materials), Dr. Tom Schumacher, SDSU (retired) shows us how important soil structure or soil architecture is for soil hydrologic function, i.e., making water infiltrate and keeping water for the next crop. Natural soils have an architecture that includes a diversity of interconnected macropores, mesopores and micropores, when soil architecture is destroyed by tillage this is equivalent to a wrecking ball to a building, so while all of the components of the building/soil remain, it no longer functions as it was originally designed. Dr. Dwayne Beck finishes off the video by emphasizing that in natural systems, TILLAGE IS A CATASTROPHIC EVENT!. While in nature, we do see catastrophic events from time to time, tillage once or twice a year is catastrophic and will serve to continually degrade the very resource the farmer depends on.
From a purely technical standpoint, Dr. Tom adds the following: “I was working on something that required a quantitative look at pore sizes and I noticed that I took liberties with my pore classification terminology used in the video. The point that I wanted to make is still valid that pores of different sizes are important for different functions. However I do not want to get you in trouble with “pore size taxonomists”. There are several classification systems for mesopores and micropores. To make a point I used my own classification tht does not match the commonly used Luxmore, 1981 classification of greater than 1 mm (1000 um) macropores; 10-1000 um mesopores; less than 10 um micorpores. Pores greater than 1 mm drain quickly, pores between 1000 um and 30 um drain more slowly but are usually empty at field capacity (around 3 days after being saturated), pores between either 30 and 10 um (depending on if sand or clay) and 3 um hold water that is easily available to crops, pores between 3 and 0.6 um hold water that is less available to the crop slowing growth, pores 0.6 to o.3 um hold water that is more difficult for plants likely resulting in stress, pores 0.3 to 0.2 um hold water that is difficult for crops to extract and will likely result in significant wilting but recovery at night under low transpiration., pores less than 0.2 um in diameter hold water unavailable to most crops, they wilt and do not recover. As you can see I oversimplified the terminology to make a point, and you may wish to clarify.”