A word to gardeners from an engineer

A little while ago, gardener & author David the Good broadcasted his creation of terra preta on Youtube, which is a layered soil and detritus mixture that has the potential for long term fertility. One of the components were broken pottery shards. One of his video commenters mentioned seeing plants prospering next to some old bricks, which are also fired clay. 

I emailed to ask if the function to improve drainage like vermiculite or perlite. He agreed that they were probably alike.

Thinking about it again, I think that the desired property is the stabilized porosity. The weight of the soil above can compact the soil, which will squeeze out the spaces. Fired pottery or porous bricks do not compress under the weight of several feet of soil. From an engineering perspective, dense and less pervious brick is desired. A gardener would want the most porous brick with the highest water absorption.

In another video a woman cultivated a microbe rich mixture, then shot it through a sprinkler. While the exposure to oxygen was brief, the injected air & hang time could not have helped the microbes survive. In fact, the environmental engineers call it biological oxygen demand (BOD), the calculated aeration that a river, stream, or body of water needs to freshen itself.

Here is a rule of thumb:  when it comes to fertility, do the opposite of what civil engineers do.

In geotechinical engineering class, students receive dire warnings about the water retention & looseness of organic soils. Large buildings crack where there are large soil movement. Fertile soil compresses a lot under weight as the air and water spaces and plant fibers deform under the massed weight of  the building. Cracked building can become unstable and result in collapse. The seal against weather is broken, leading to infiltration of mold and mildew as moisture gathers in the building. These infiltrators can cause serious heath conditions in humans as well as eat building components. Inviting the great outdoors into the indoors is a death sentence for electronics and machinery.

The variability of life also translates into variable soil stiffness and strength. These all make construction more difficult and costly as soil remediation, such as compaction, mixing cement into the ground, or adding gravel to the ground. 

All of these actions directly contradict what farmers and garderners do. A tractor loosens soil, at least in the short term, while a compactor will densify. In fact there are tests & methods to find the optimum soil wetness and number of runs of the compactor to achieve density. Cement plus soil hardens into a low-strength concrete known as soilcrete. Imagine trying to plow that. Gravel are pieces of hard rock & provides a stiffer surface for vehicles to drive over, which is why it is used for driveways. Holes are also drilled in the ground & gravel is compacted in to make stone piers, as an alternative to piles or concrete piers.

The simplest solution would be to not build in organic soils. This was the solution for millennia as many cities were built in land that the farmers couldn't use. This was typically harder and firmer soil than the surrounding area. There are cities built on river deltas such as New Orleans or swamps, like DC or St. Petersburg. 

However, government managed to foul even that up in my hometown, which passed brownfield legislation years ago. Any industrial site (brownfield) must be restored to pristine condition prior to reuse. This applies even if the new occupant is another industrial use. That added cost incentivizes buying out farming land for conversion to industry and housing. 

Keep in mind that the original urban site was chosen, because it was was on hard land that was unsuitable for agriculture. The urban site also became enmeshed in the transportation system. The double whammy comes in with resources spent to extend the transportation system and the utilities. The site also has to be prepared with the aforementioned compaction or piles to rest on the soft soil in addition to paving. 

It's lose lose all around. The lawmakers came in the spirit of wrath; to punish someone, anyone, for polluting the ground. This in contrast to the spirit of cooperation to put that patch of land back into use with a measured requirement to restore the land to usable, not pristine. Instead of putting money into iron fisted enforcement, put money in incentive directly for the restoration, to restore the land into use & restore jobs back into the cities.

Amend that, gardeners, when it comes to fertility, do the opposite of engineers & gardeners.