Can Calcium Fertilizers Enhance Soil Well being or Crop Manufacturing in Alfalfa?

By Roland D Meyer and Daniel H. Putnam


Can functions of Calcium (Ca) fertilizers enhance plant nutrient uptake or enhance soil properties in alfalfa fields?

These questions have been offered to us by an alfalfa grower within the Sacramento Valley of California the place low soil Ca ranges have been noticed.

Soil samples have been taken from 9 totally different alfalfa fields in Yolo County within the fall of 2021 to evaluate nutrient wants. This farmer had executed a wonderful job of sustaining P and Ok ranges, however calcium ranges have been usually low: starting from 1.0 – 4.0 meq/l. Something lower than 4.0 meq/l calcium is taken into account very low.  Have been these calcium ranges too low and limiting to plant development and alfalfa yields in these fields?

Ca Nutrient Wants of Alfalfa. Calcium is a necessary nutrient for plant development, one among 17 ‘important vitamins’ for all crops. Ca is taken into account a ‘macro-nutrient’, that’s, a component wanted in giant portions. Magnesium (Mg) can also be a necessary nutrient wanted in giant portions. An 8 ton/acre alfalfa crop removes about 256 lbs. of Ca and 53 lbs. Mg per 12 months, so calls for for Ca are a lot larger than for Mg (Meyer et al., 2007). Though the focus in these soil studies for Ca have been low, they’re possible nonetheless enough to fulfill the annual crop uptake and elimination ranges for crop manufacturing (though long-term depletion of Ca must be of concern). We’ve not seen any information that means that functions of Calcium appropriate the nutrient wants of alfalfa to enhance yields or that Ca is limiting in California soils, and even nationally.

However that is not the one consideration.

Ca: Mg Ratios. The ratios of Ca to Mg in soils are essential as a result of these minerals usually compete with one another for uptake by crops. Each are 2+ constructive ions (CA++, Mg++). For nutrient deficiencies to happen in alfalfa fields, Ca:Mg soil ratios would have to be very low, round 1:4, or very excessive in calcareous soils (Determine 1, Simpson et al., 1979).

Determine 1. Vary in Ca:Mg ratios over which no yield despair has been noticed in alfalfa. Alfalfa is well-adapted to a variety in Ca:Mg ratio ranges (graph from Simson et al. 1979). Ca isn’t noticed as a limiting nutrient in alfalfa manufacturing.

Fortuitously, alfalfa is well-adapted to a variety of Ca ranges, in addition to a variety of Ca:Mg ratios in soils. Alfalfa solely exhibiting sensitivity and yield losses at extraordinarily excessive or low ranges of both Ca or Mg (Determine 1). Simpson et al., (1979) concluded that at a impartial pH, alfalfa yields wouldn’t be a lot affected by various Ca:Mg ratios. In a number of research, there may be a variety in Ca:Mg ratios over which no yield despair has been noticed (Simson et al. 1979). The soil analyses on this Yolo County case revealed that the ratio of Ca:Mg ranged from 0.6-1.3 meq/l (Determine 2), nonetheless within the good vary to fulfill the plant wants for calcium (Determine 2).

Normally, Yolo County soils are likely to have considerably larger Mg ranges attributable to mum or dad serpentine soils within the coastal mountains. Extra analyses in these soils samples from the 9 totally different fields confirmed Potassium (Ok) starting from 0.3 – 1.3%, Sodium (Na) 0.5 – 2.3%, and Boron (B) 0.7-2.2 ppm. Boron additionally tends to be larger attributable to historic borax deposits in the identical watershed.


Determine 2. Vary of Ca:Mg ratios reported within the soil evaluation for 9 alfalfa fields (some sampled twice) in Yolo County in 2021. These are throughout the vary for no yield losses related to manufacturing (Determine 1).


Nonetheless, that is not the entire story. It is also essential to have a look at soil properties (‘soil well being’).  These are components comparable to aeration, crusting, compaction, natural matter, and water infiltration. The ratio of Ca to Mg might also have an effect on water infiltration charges, crusting, and soil losses on particular soils which might be liable to sealing (Dontsova and Norton, 2001). Determine 3 exhibits the impact of both excessive Mg or excessive Ca on flocculation of soils and water infiltration from their work. These researchers discovered that in well-structured soils, Ca-treated soils had infiltration charges double that of Mg-treated soils (Dontsova and Norton, 2001).   Ca-treated soils diminished suspension and soil erosion losses, which beneath irrigation may scale back erosion and particle contamination of floor waters.


Determine 3. Excessive Calcium ratios (a-e vary from 0:100 to 100:0 Ca:Mg ratio, left) improves flocculation, reduces soil suspension (left picture). Excessive Calcium additionally considerably improved infiltration charges. (Knowledge from Dontsova and Norton, 2001). Flocculation improves water infiltration and prevents runoff attributable to growth of bigger macro-pores. Blount is a selected soil kind.

So additions of excessive Ca containing amendments (comparable to gypsum) may have profound impacts on soil high quality and well being.

These soil properties could also be extra essential than the amount of Ca out there for plant vitamin. Excessive Ca:Mg ratios might enhance floor water infiltration, scale back runoff and enhance aeration. It is also well-known that additions of gypsum (Calcium Sulfate or CaSO4) improves soil water infiltration because of the alternative of sodium (Na) with Ca on soil particles. Though these Yolo soils will not be notably excessive in sodium, the addition of gypsum might also serve to enhance water infiltration and soil properties attributable to improved Ca:Mg ratios in addition to changing the Na on the soil coloids.

No Ideally suited Ratio.  Though some labs and agronomists have promoted an ‘splendid’ ratio of Ca:Mg (and Ok), evaluation of the info has proven that, though excessive Ca is essential, there may be actually no splendid ratio of those cations that enhance plant development or soil properties (Kopittke and Menzies, 2007).


Addition of gypsum is extremely really helpful to enhance soil properties on these soils, however not essentially to enhance Ca vitamin for alfalfa.  Ca concentrations and Ca:Mg ratios are in a superb vary for alfalfa manufacturing in these Yolo County alfalfa fields sampled, and we’re will not be conscious of information that signifies Ca as a serious limiting issue for plant development or Ca uptake.   However additions of Ca-rich amendments are prone to positively influence soil high quality (improved water infiltration, diminished crusting), which in flip, may enhance yields.  Low Ca:Mg ratios might trigger crusting of soils after rain or irrigation occasions, trigger extra runoff, and poor water infiltration. That is essential for agriculture but additionally environmentally, since off-site motion of particulates are an issue for soil erosion and contamination of floor waters with soil (and pesticides connected to soils!). These infiltration points are primarily an issue within the high ¼ to 1” of soil, thus floor utility is really helpful vs. incorporation. For soils with lower than 1:1 ratio of Ca:Mg, a advice can be to use gypsum at 2 tons per acre or larger on the soil floor for present stands to enhance water infiltration, stop soil erosion and runoff and floor water air pollution. That is additionally essential throughout stand institution simply after seeding the alfalfa fields to assist stop crusting of the soil, guaranteeing good seedling emergence and stand institution.


Photograph: Gypsum being utilized to an alfalfa subject in Yolo County at 3 tons/ac within the fall of 2021 to judge impacts on calcium ranges within the soil in a UC Cooperative Extension trial.

Extra Notes on Soil Sampling:   Quite a lot of totally different soil exams can be utilized to judge calcium and magnesium concentrations in soil. One of many extra widespread is utilizing the cation change capability or (CEC). That is normally expressed by way of milliequivalents per 100 grams soil or meq/100g soil. Soil exams will normally give the concentrations of calcium (Ca), magnesium (Mg), potassium (Ok) and sodium (Na). These symbolize the extra essential cations within the soil that characterize each soil and plant rising circumstances for favorable plant development.

  • Calcium:Take into account the Ca focus as a share of the whole cation change capability (CEC). For good soils and plant development, it must be within the vary of 55% ± 5% of the CEC. Increased than 70-75% Ca, then the magnesium (Mg) must be round 20% or barely larger for good stability. Whether it is a lot larger, say 40-50% magnesium, then there could also be crusting of soils following a rain or irrigation and poor water infiltration. Growing the proportion of calcium focus or lowering the magnesium focus requires giant quantities of gypsum or different sources of calcium to change the proportion of calcium.
  • Magnesium: Having set the calcium focus, we’ll transfer on to magnesium. The magnesium focus ought to at all times be lower than the calcium focus, maybe 20-40% of the whole cation change capability (CEC)
  • Potassium: A good vary of potassium in soils is normally about 2% of the CEC or much less. Ample concentrations are normally given in ppm of exchangeable Ok at about 100 ppm to 150 ppm or above.
  • Sodium: Since sodium shouldn’t be a necessary nutrient for plant development, the necessity for sodium within the soil is minimal, as close to to zero as doable.

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