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11339Re: soil moisture: data

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  • shultonus
    Dec 26, 2010
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      While nothing wrong has been said regard to soil moisture...

      I would like to clarify a couple of things...

      1) The primary factor controlling plant available water is the
      soil texture. Basically, the more clay you have in your soil the more water it can hold.
      This is a simple physical equation that is based on surface area.

      Sandy soils will hold 4cm of water with 1-3cm of water available for plants in the top 30cm
      Loamy soils (mix of sand, silt and clay) will hold 8.5 cm of water with 5cm of water available for plants
      Clay soils will hold 11cm of water with 3-4cm of water available for plants

      you can refine this more based on the minerology of the the clay portions:
      In general red clays are kaolinite and iron oxides (hematite).
      Kaolinite is low potential fertility large clay
      THe iron floculates (sticks together) the clay so it acts more like silt then clay

      gray/black clays that develop large cracks (greater than 2cm) when dry are smectites they have better potential fertility and are much smaller

      there are dozens of other kinds of clays, but you need an x-ray diffraction machine to figure out what they are.

      Now for the heart of the question:
      Organic matter absolutely has a HUGE impact on soil water relations:

      A typical value for organic matter is it will hold 3 TIMES its own weight in water!!

      Technically it depends on what the original vegetation was and how decomposed it is so this might very between 1 and 5 times.

      For example: a bad tropical soil might have 0.5% SOC
      while a really good tropical soil might have 1.5% SOC
      A good midwestern soil in the USA might have 2-4%

      The maximum amount of organic matter is limited by the average temperature and modified by the wetness/dryness of the climate.

      Then under typical farming the maximum is lowered by plowing
      and other practices(artifical fertilizers).

      So back to the question:
      we are talking about 1% difference in SOC (soil organic carbon)
      (this is the measurement scientists make)
      Because organic matter is ~40% carbon, we multiply the SOC
      by 1.7 to get 1.7% difference in organic matter

      so a typical soil is 1.2-1.6 g/cm3 this is the bulk density

      so 1.7% times 1.3 equals 0.02 g/cm3 organic

      so 30cm deep (1x1 column)= 0.6g organic
      which will hold 1.8 grams of water which converts to
      an extra 1.8cm of water available in the good soil vs bad soil
      Which is a 50%+ improvement in available water

      Now for long term organic systems that add manure and such,
      it is not unheard of to approach 10% organic matter
      but this requires large amounts of mulches and manures.

      More importantly organic matter has two other profound effects on plants.
      Organic matter is like a bank of fertility locked within the organic matter are plant nutrients that are slowly released as the organic mater decomposes.
      But the organic matter also is like a magnet, and will hold the plant nutrient in the soil with less leaching (loss)

      And finally the organic matter creates good soil structure, which allows rain to get into the soil instead of running off.
      --- In fukuoka_farming@yahoogroups.com, Sundaresan A <sundaresanma@...> wrote:
      > dear suman
      > the water holding capacity of soil depends on various factors
      > 1.total organic carbon in soil
      > 2. soil mineral charactertics, humus and mineral bondage including electro chemical properties _ cation and anion behaviour
      > 3.climatic conditions
      > 4.hydrogical cycle
      > 5.supporting eco system
      > 6. atmospheric temperature
      > in general, the more amount of humus present in soil as in case of nf , the water rwtention capacity is more
      > a.sundaresan
      > ooty
      > On Fri Dec 24th, 2010 5:56 PM IST Sumant Joshi wrote:
      > >I want to know how much water good soil can hold vis-a-vis depleted soil. Lets say we begin with 1 kg of dry soil each and pour water into it. How much can either type hold without runoff? it is I think the key to flash floods and drying up of wells in our area.
      > >
      > >Sent from my BSNL landline B-fone
      > >
      > >Warm regards,
      > >
      > >Sumant Joshi
      > >Tel - 09370010424, 0253-2361161
      > >
      > >--- On Fri, 24/12/10, Raju Titus <rajuktitus@...> wrote:
      > >
      > >From: Raju Titus <rajuktitus@...>
      > >Subject: Re: [fukuoka_farming] soil moisture
      > >To: fukuoka_farming@yahoogroups.com
      > >Date: Friday, 24 December, 2010, 4:45 PM
      > >
      > >Dear friend,
      > >Moisture of spoil is dependent on the availability of Root zone . As much
      > >deeper and dense roots are water is present and there is no limit of this.
      > >Thanks
      > >Raju
      > >
      > >On Fri, Dec 24, 2010 at 3:39 PM, Sumant Joshi <sumant_jo@...> wrote:
      > >
      > >>
      > >>
      > >> Hi,
      > >> Has anyone done any research or at least has experience of how much water
      > >> real soil (fertile with lots of organic matter) can hold by weight compared
      > >> to depleted soil?
      > >> I need the data for a little research I am doing. I think the soil in a
      > >> natural farm will be the best for the study.
      > >>
      > >> Sent from my BSNL landline B-fone
      > >>
      > >> Warm regards,
      > >>
      > >> Sumant Joshi
      > >> Tel - 09370010424, 0253-2361161
      > >>
      > >> [Non-text portions of this message have been removed]
      > >>
      > >> 
      > >>
      > >
      > >
      > >
      > >--
      > >Raju Titus. Hoshangabad. 461001.India.
      > >+919179738049 begin_of_the_skype_highlighting              +919179738049      end_of_the_skype_highlighting.
      > >http://picasaweb.google.com/rajuktitus<http://picasawebalbum.google.com/rajuktitus>
      > >fukuoka_farming yahoogroup
      > >
      > >
      > >[Non-text portions of this message have been removed]
      > >
      > >
      > >
      > >------------------------------------
      > >
      > >Yahoo! Groups Links
      > >
      > >
      > >
      > >
      > >
      > >
      > >
      > >[Non-text portions of this message have been removed]
      > >
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