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According to the US Department of Agriculture (USDA):

Increasing soil organic matter increases the ability of soil to hold droplets of water.  This process is called soil water holding capacity. 

As the organic matter in soil increases:

  • Surface structure becomes more stable and less prone to crusting and erosion. (“improved tilth”)
  • Water infiltration increases and runoff decreases when soil structure improves.
  • Soil organic matter holds 10 to 1,000 times more water and nutrients.
  • Beneficial soil organisms become more numerous and active with diverse crop rotations and higher organic matter levels. In other words, increasing soil organic matter increases soil resistance to drought conditions.  As a result, it provides an opportunity to reduce irrigation water use.
  • Increasing soil organic matter by 1% increases soil moisture by 20,000 gallons/ac.

Here is a reference on this topic by the USDA Natural Resources Conservation Service (NRCS) …

Role of Soil Organic Matter | NRCS Soils Role of Soil Organic Matter. Once a land manager begins working towards enhancing soil organic matter, a series of soil changes and environmental benefits follow. The rate and degree of these changes and the best suite of practices needed to achieve results vary with soil and climate.

 Where does organic matter come from and how can farms of all sizes increase soil organic matter? Adding organic matter to soil begins through development of regenerative agricultural practices.  

Regenerative agriculture depends upon doing the following:

  • keeping living (green) material in the soil around the year as much as practicable. For most farmers this can initially be achieved by initially introducing straw, manure, leaf mulch etc., and/or longer-term growing cover crops (green manure) then lightly tilling the cover crops in to a shallow soil surface.
  • keeping a cover residue of living/dead plant material on the soil surface at all times
  • reducing (preferably eliminating) plowing and tillage practices (minimize soil disturbances)
  • withholding use of synthetic chemical pesticides as much as practicable
  • optionally introducing livestock to increase economic and biological diversity (sheep, poultry, goats, beef, etc).

The overall documented suggestions are to use some/all of the practices of regenerative agriculture to increase soil organic matter (SOM).  The SOM improves soil ecosystem health that has a much stronger water holding capacity.  Growers then can keep an eye on their crops and/or use probes to measure soil moisture. There are many places where soil moisture probes can be obtained through the internet for less than $100.  Growers with soil containing increased SOM will be able to reduce irrigation frequency and amounts. 

Neighbors could share one probe.

To get started this year on increasing SOM, a normally slow process, growers can add straw to their topsoil.  Purchase the cheapest straw available, generally free from contaminating seeds, and apply as much as is practicable to the topsoil.

Obviously growing cover crops and leaving plant residues will be less expensive but this takes time to significantly increase SOM.  In the Fall, leaves are generally a free source of plant organic matter to add to topsoil. This plant source might be mainly applicable to smaller farms and backyard gardens.

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