SINGLE SEASON PHOSPhate AVAILABILITY


PHOSPHATE SOIL FIXATION

Soil fixation results in the loss of nutrients such as sulfate phosphate, and cation nutrients.

Up to 75-95% of the phosphate fertilizer applied to your soil is unavailable to the roots of your crops. It becomes insoluble in the soil due to fixation with: calcium, iron, aluminum and magnesium.

Whether in soil, water, or applied as fertilizer, the elements absorbed by the plant (in ionic form) tend to form insoluble compounds. Once solid compounds are formed, the nutrients are unavailable to the plant.

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In alkaline soil, low solubility calcium phosphate is formed.

In acidic soils, phosphate ions react with Fe and Al to form insoluble compounds.

PHOSPHATE AVAILABILITY IN SOIL

 DIAGRAM ILLUSTRATING MAXIMUM PHOSPHOROUS AVAILABILITY IN SOILS. THE CHART HIGHLIGHTS THE LIMITED AVAILABILITY OF PHOSPHOROUS. THIS GRAPH ASSUMES AVAILABILITY AT AN OPTIML PH FOR PHOSPHOROUS AVAILABILITY OF 7.  IF PH IS BELOW 6.5 OR ABOVE 7.5 PHOSPHOROUS AVAILABILITY CAN BE REDUCED BY AT LEAST 50% FROM THE CHART ABOVE. 

The above diagram highlights the limited phosphate availability in soils. The graph above shows average phosphate availability of both liquid and dry phosphate under wet and dry soils. These % assume a optimal pH level for phosphate availability of 7. 

If the pH is below 6.5 or above 7.5 phosphate availability can be under 50% of the values above.


PHOSPHATE FERTILIZER IS NOT COMPATIBLE WITH:

  • Calcareous soil
  • Low pH soils high in iron
  • Soils high in aluminum
  • Water with a high CEC
  • Irrigation water with an excess of ions such as (Ca, Mg, Zn, Fe)