Digging Deeper Case #10 Calcium ferts & surfactants to improve infiltration

THE SITUATION: 

Early June: The field has severe symptoms of poor water infiltration. It’s not the first time that ponding/runoff has been a problem on this ranch, but it is more severe than in previous years and with high temperatures on the forecast, an immediate solution is required. Symptoms suggest that the poor infiltration is due to soil deflocculation, probably due to poor water chemistry. It was recommended by agronomists that the grower apply calcium fertilizers and a soil surfactant as an immediate but likely short term solution to the problem. Will this work, and how long will the benefits last?

HEre’s what the scene looks like: 

SYMPTOMS:

• Water runoff and ponding throughout the field; problem was noticeable early-season and has gotten progressively worse. The ponding/runoff pattern is throughout the field, under the drippers, along the berms, and in the rows, pointing to soil deflocculation as the cause, and not compaction.
• Soil became physically harder as season progressed due to increasing dryness of soil below the surface
• In-field soil moisture sensor data shows little to no water infiltration at the 8″ depth during and after each irrigation event (see Chart 1 below at June). Early season infiltration was only slightly better than in July.

FIELD INFO:

• Variety: Butte and Padre almonds
• Age: ~10 yrs.
• Location: Madera, CA
• Irrigation: Dual-line drip. Early-season surface water from district, mid-to-late season switch to well water.
• Block size: 35 acres, symptoms seen throughout
• Soil texture: Medium-heavy, no significant variability
• Field has had infiltration issues for several years; symptoms this year look similar to previous years, but are more severe
• Field-spread gypsum has been applied in previous years during dormancy, including an application approx. 7 months ago at their typical rate. No significant amount of calcium fertilizers or other calcium materials have been applied in the past year.
• According to recent water and soil analyses, both the water and soil have a low EC and are low in soluble calcium (both well under target levels). In addition to visible runoff and ponding, this makes a strong case that the issue is deflocculation due to low-EC, low-calcium irrigation water.
• Water infiltration issues are common in this region where similar irrigation water sources are used.

Here’s what WE KNOW ABOUT POOR WATER INFILTRATION, Soil surfactants and CALCIUM FERTILIZERS: 

• Poor water infiltration has three primary causes: soil deflocculation, poor aggregation, and compaction.
  • Soil deflocculation: This is when the minerals in the soil which hold soil particles apart are not present and the soil collapses. It’s a soil chemistry issue, whereas poor aggregation and compaction are primarily physical issues. Specific minerals (especially soluble calcium) hold clay particles apart which creates space through which water can pass. When calcium is insufficient or outnumbered by deflocculating minerals like sodium or bicarbonate, the clay particles’ structure collapses and prevents water from passing.
    • Deflocculation can be diagnosed by looking at the EC, calcium, and a handful of other ions on soil and water analyses.
    • Commonly, deflocculation is caused by long-term use of low EC water, and in such cases the best solution is to amend the water.
    • In many cases, adding soluble calcium can improve water infiltration fairly immediately, assuming that the calcium can somehow get deep enough into the soil. However, if the deflocculation is due to poor water chemistry, the problem will return with subsequent irrigations. For these reasons, addressing deflocculation with soil surfactants and/or calcium fertilizers may produce an immediate improvement of water infiltration, but it will likely be temporary.
  • Poor soil aggregation: This is when soil particles are held together by organic matter and residues produced by living organisms in the soil, which creates large pore spaces for water to pass through. Whereas soluble calcium create micro pores in the soil, aggregation produces macro pores. Both micro and macro pores are important for good water infiltration. Cover crops, applications of compost and other organic matter, and any other soil biology-friendly practices build soil aggregation, whereas things like removal of crop residues, excessive tillage, and exposure to the elements can negatively impact soil aggregation over time.
    • Due to the traditional farming practice of non-tillage, production almond blocks tend to have lower levels of organic matter and, subsequently, soil microbiology and aggregation. This is because almonds are easier to manage (specifically harvest) when there is minimal vegetation and crop residues around the trees, so practices that keep the ground clear are prioritized above those that build soil organic matter and aggregation.
    • Soil aggregation takes time to build. For this reason, many practices that improve soil aggregation are unlikely to produce immediate improvement of water infiltration. .
  • Soil compaction: This is when the soil is physically “smashed” so that the pore spaces through which water typically moves are compacted. It’s commonly created by equipment driving on wet dirt, particularly in fields with heavier-textured soil. Classic symptoms for soil compaction include ponding in wheel ruts or at the ends of rows.
    • Compaction is typically addressed with tillage. 

• Soil surfactants are polymer-based materials which break the surface tension of irrigation water, allowing it to move through smaller pore spaces than it otherwise would be able to. This effect is only a temporary solution since soil surfactants generally do not restore pore space, and they do not remain in the soil in sufficient concentrations for the next time water needs to pass through. 

• Calcium fertilizers: There are several kinds of calcium fertilizers, including CAN-17, CN-9, and CaTS. Calcium fertilizers contain an immediately plant-available form of calcium and are intended to be applied at rates and timings required for plant nutrition. They can be used as a soil amendment if used in sufficient quantity but their high cost-per-unit compared to other sources of calcium (such as gypsum) and the potential for “tagalong toxicity” make them inefficient and sometimes problematic as a soil amendment. For this reason, calcium fertilizers are typically not recommended as an economical, long-term solution for water infiltration issues.

  Check out the “Pounds on the Ground” reference for a more in-depth comparison of calcium materials.

What was applied

• Application #1: 10 gpa CaTS + 10 gpa surfactant (early July)

• Application #2: 10gpa CaTS only (early August)

• Application #3: Begin regular schedule of 10gpa CaTS + 10 gpasurfactant (early September)

CONNECTING THE DOTS

Let’s take a closer look at the results from these three applications and what may have caused them.

application #1: 

The recommendation was made to apply calcium thiosulfate with a soil surfactant to get calcium into the soil as quickly as possible. It was applied early July.

Results:

• Ponding visibly decreased
• Soil moisture sensor data showed infiltration at both the 8″ and 16″ depths
• Results lasted for 5-6 irrigations, and then the infiltration problems returned

Check it out on the moisture sensor data analysis (above):

• First irrigation – significant infiltration at 8″ sensor
• Third irrigation – significant infiltration down to 16″ sensor
• Sixth irrigation – improved infiltration effects beginning to decline
• Eighth irrigation – Infiltration returned to pre-application levels

Why did this happen?

The combination of CaTS + soil surfactant improved infiltration almost immediately. The soil surfactant carried water and CaTS below layer of deflocculated soil, allowing calcium to open up the soil structure.

• Calcium fertilizers alone, when applied at these rates, can flocculate a soil but they can take time to work their way through deflocculated soil. 
• Soil surfactants effectively allow water to move deeper in the soil but after 1-2 irrigations they spread out in the soil and are no longer concentrated enough to produce the desired effect. Soil surfactants alone do not improve soil structure, so it was the effect of the calcium that allowed the improved infiltration to last for multiple irrigations.
• The effect of the calcium wore out after several irrigations with low-calcium water. Low calcium water can strip calcium from the soil, which is how this soil became deflocculated in the first place.

application #2: 

Once the results from application #1 wore off, it was decided to apply CaTS alone to see if the infiltration improvement could be recreated without the surfactant.

Results:

• Visibly there were no improvements at these rates
• Soil moisture sensor data showed infiltration at 8″
• Results lasted 1-2 irrigations.

Check it out on the moisture sensor data analysis (above):

• First irrigation – significant infiltration down to 8″ sensor
• Second irrigation – no significant infiltration at any depth

Why did this happen?

The application of CaTS by itself provided calcium which appears to have improved the soil structure, but the effects were shallow. Without the surfactant to carry the calcium deeper into the soil, the effects were only 8″ deep and only lasted for a 1-2 irrigations. This second application shows two important things:

1. The surfactant plays a key role in getting the calcium into the soil so that the results aren’t just on the surface, and
2. The effects of CaTS alone and CaTS + surfactant wear off within a few irrigations, so repeat applications are necessary to maintain improvements.

application #3: 

Based on the results of the first two applications, it was determined that both materials were needed for maximum effect. A regular schedule of calcium thiosulfate and surfactant was started and continued through the rest of the season. August 31-Sept5 grower used pulse irrigation to help water infiltrate smoother.

Results:

• Ponding and runoff almost entirely gone
• Soil moisture sensor data showed that infiltration reached all the way to the 48″ depth within a few irrigations.

Check it out on the moisture sensor data analysis (above):

First irrigation(s) – significant irrigation down to 36″ sensor

• Second irrigation – significant infiltration down to 48″ sensor
• Fourth irrigation – noticeable infiltration down to 60″ sensor
• Subsequent irrigations – continued significant infiltration down to 60″

Why did this happen?

Repeat applications of CaTS + surfactant produced impressive results. Applying both materials, repeatedly, allowed water to infiltrate to 24″ and all the way to 48″ shortly thereafter – which was significantly deeper than what was achieved with a single application. Instead of the effects wearing off, they compounded.

CASE WRAP-UP 

The application of both a calcium fertilizer and a surfactant did help remedy the infiltration issues. The results were temporary with a single application, and the results with repeat applications were sustained and compounded. Repeat applications were necessary because, when applied at typical rates, calcium fertilizers lack the quantity of soluble calcium necessary to solve infiltration issues. As we saw after application #2, the quantity of soluble calcium that was applied simply wasn’t enough to have a lasting effect. 

The source of calcium was effective, but not economically ideal. Since the cause of the infiltration issues was primarily due to water chemistry (low EC, low calcium), the most economic way to solve the problem would be to amend the water with gypsum. At this time of this case, solution machines are the method that allows the maximum rate of soluble calcium to be applied to a field. The initial equipment costs are higher, but the operational costs (CaTS vs solution-grade gypsum) are significantly lower. Getting the equipment installed and getting your team trained may require some lead time so it’s best to start the process well before the symptoms are severe. 

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Thank you Mark Veteto from Source to Source for letting us dig deeper with you on this case!