Gyp in June

Written by: Franz Niederholzer, UC Farm Advisor, Colusa/Sutter/Yuba Counties,  Allan Fulton, UC Farm Advisor, Tehama/Shasta/Glenn/Colusa Counties

It’s June – the best time to apply gypsum to the soil surface in orchards with flood or wide coverage sprinklers.  Why now?

But first, what does gypsum do and not do?  Adding gypsum to the soil can significantly increase the rate of irrigation water infiltration when using 1) very clean (usually canal/surface) irrigation water (EC < 0.5 dS/m); 2) when the soil surface sodium adsorption ration (SAR) is 5 to 10x that of the irrigation water EC; or 3) when calcium to magnesium ratios in the water are not at least 1:1.  Adding gypsum also provides additional calcium and sulfate for nutrition, if needed.  Gypsum, calcium sulfate, is a neutral salt so it affects soil pH very slowly causing it to seek neutral soil pH (7.0).  It won’t break up hard pans or soil layers with distinctly different soil textures or compaction that impede water infiltration.  Gypsum stabilizes the soil.  It reduces dispersion of larger soil aggregates when a dry soil is irrigated.  In turn this reduces the formation of soil crusts and helps maintain more soil porosity and higher water intake rates.

How much gypsum is recommended to improve irrigation water infiltration for the conditions described above?

  • Injecting 500 to 1000 lbs finely ground gypsum per acre foot of water should increase irrigation water EC by 0.15-0.3 dS/m, enough to improve infiltration of very clean water or reduce the effects of sodium and magnesium.
  • If not using micro-irrigation, broadcast up to one ton/acre of finely ground gypsum onto the soil surface and do not till it into the soil.  It will dissolve in the water as irrigations are applied and improve the water quality.  The best time to apply gypsum on the soil surface to improve irrigation water infiltration is in June, when soil infiltration rates tend to decline and as higher summer temperatures (and water use) set in.    The effect on infiltration may diminish after about 12 inches or more water has been applied and infiltrated into the soil, carrying the calcium deeper into the soil so it no longer amends the water quality.
  • If the benefit of the gypsum appears to wear off, a second application might be needed.  One application at a higher rate of up to four tons per acre may be considered as a more practical and attractive alternative.  The potential problem is that the single application at a higher rate may result in much higher concentrations of dissolved calcium than is actually needed to improve the irrigation water quality and infiltration so the calcium is quickly leached below the top few inches of surface soil after only a few irrigations.  Then the calcium levels are not sufficiently elevated during later irrigations and slower infiltration rates resume.  In almond growing regions that receive more winter rainfall, higher rates of gypsum will leach deeper into the soil profile during the winter and will not be as effective to improve water infiltration at the soil surface the next season.  The money spent for higher rates of gypsum to manage slow infiltration could be saved for more timely use.

Bob Beede, UC Farm Advisor in Kings County, put it this way years ago – “Gyp in June”.

Print Friendly, PDF & Email

5 thoughts on “Gyp in June

  1. I farm almonds in the hills on the east side of Stanislaus county. I irrigate with dual line drip. I have started having penetration issues is the last two weeks. I have broadcast two tons of gyp per acre. One application in late fall and another application mid spring. I have also applied 4 tons of gyp through the irrigation system. (Irrigation system is 1400 GPM) I am able to monitor soil moisture thru a Puresense setup. Irrigation response has been perfect until the last two weeks and now the lower profiles have started dropping off. Any advice would be greatly appreciated.

    Thank you,
    Jeremy


    1. Jeremy,
      Sounds like your trees aren’t getting enough water – either because the water is not getting to the deeper depths of the soil or not enough is being applied. Is the water running off the soil or is it infiltrating? If infiltrating into the soil, how much water are you applying per tree, acre? What are your irrigation frequencies, run times, and emitter spacings and flows? Are you calculating ETc and reapplying used water or just trying to keep it in the color bars on the pursense system. If the water is running off the soil, have you conducted a water and soil analysis? If this is too much to type, it would be useful to contact your local farm advisor, Roger Duncan – 209-525-6800.

      David


      1. David,

        The water is not infiltrating. My emitter spacing is every four feet and they are .5 gph emitters. A 24 hr set nets me a .5 inch of applied water. I water using etc. I don’t base my irrigations off of the Puresense charts. We just conducted a water analysis but have not done a soil analysis recently. I actually contacted my PCA yesterday about doing a soil analysis. Our water looked good with the exception of a high bacteria count which we are countering with copper sulfate.

        Jeremy


        1. Thanks for the follow up comment. A water and soil analysis will be/is the best place to start. The water analysis will tell you what you are applying while the soil analysis will indicate what is accumulating. When the results are returned, I strongly urge you to call your farm advisor to go through the results. You can email me the results as well, but sometimes knowing the local conditions helps.

          As a side note – The aquifers in Merced that are in the rolling hills of the east side often have high magnesium, which can gradually impact infiltration over time as it accumulates in the soil.

          David


          1. David,
            Thank you for your input. I contacted Roger this morning and pulled samples as well.

            Thank you,
            Jeremy


Leave a Reply

Your email address will not be published. Required fields are marked *