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I am reading a gardening book and encountered (three times in fifty pages) the statement

Roughening up* the soil reduces water evaporation. Especially in the presence of caked up topsoil.

My intuition is opposite - aerated soils loose water; caked soil prevents it as if someone laid concrete on top.

Does working the soil reduce or increase moisture evaporation?

* - rough translation. Surface treatment. Working the top 15cm of the soil.

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"Roughening up the soil" is a rather odd term for a gardening book. Assuming that the author means surface tilling, then he or she is probably incorrect. The opposite of surface tilling is conservation tillage, which allows at least some plant residue to remain on top of the soil over the winter. It is usually used to help prevent water and wind erosion, and, according to the 5th Edition of Soil Science and Management by Edward Plaster (c. 2009):

...conservation tillage increases soil moisture by improving infiltration and reducing runoff, reducing evaporation, and trapping snow [in the plant residue]... Conservation tillage also increases biological diversity in the field... this means more diverse soil microflora, more diverse insect populationns, as well as higher numbers of earthworms.

So, the opposite effect listed in your gardening book. Unless your caked soil also contains vegetable/plant residue, it is not an example of conservation tillage and actually prevents water from soaking into the soil, increasing runoff and erosion.

Now not all agricultural practices apply to home gardens, but this is as close as I could find to answer your question.

A better way to increase soil moisture content and prevent evaporation and erosion is an application of compost to increase the organic content of the soil and/or an application of at least an inch-thick layer of arborist wood chips as a mulch. With a mulch you won't ever need to till or "rough up" your soil again.

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  • Very common in US for corn and soybean fields to be cultivated during growing season It kills weeds and reduces moisture loss. Sep 15, 2021 at 15:45
  • @blacksmith - I'm assuming you mean that organic farmers cultivate between the rows, which they sometimes do by hand. In my area of Wisconsin non-organic (i.e. nearly all) farmers use RoundUp Ready seeds, so they spray. There's no need to cultivate in a garden if you use organic mulch like wood chips, cocoa bean hulls, rice hulls, pine needed, marsh hay, etc.
    – Jurp
    Sep 15, 2021 at 20:22
  • The cost of going over a field has reduced cultivation from what I remember . But there are still many internet references ; I noticed one from Purdue D. of Ag. noting cultivation helped reduce moisture loss ( and controlled weeds in addition to herbicide). Sep 16, 2021 at 0:55
  • @blacksmith37 Is Purdue saying that cultivation reduces moisture loss due to runoff? That's correct. But it increases moisture loss due to evaporation. There is some conflicting information out there, though. I know that many of the University of Wisconsin's Extension articles are over 30 years old and their advice is out-dated at best and flat wrong at worst, so I almost never use that Extension as a source. Purdue is OK, but I prefer Univ of Minn, Iowa State, Mich State and Wash State. Wisc's problem is massive funding cuts over the past 10 years.
    – Jurp
    Sep 16, 2021 at 10:54

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