Low Available Phosphorus


Low available phosphorus is responsible for reduced agriculture productivity in many regions globally, hindering soil health, especially in tropical regions with highly weathered soils. As soils age, soil minerals are transformed into iron and aluminum oxides. These minerals, often bright red and yellow, give these soils their vivid colors but also tightly bind P.1 They differ from the phyllosilicate minerals more commonly found in younger soils in that they do not maintain a permanent negative charge due to isomorphic substitution. Rather, many iron and aluminum oxides maintain a positive charge at acid to neutral pH and bind  tightly to the negatively charged P oxyanion, reducing availability of P for plants.2-3 Further, during the aging process, soil acidity increases and plant nutrients such as P may be lost through leaching. Methods to increase soil P availability include: 1) liming (increasing soil pH), 2) increasing soil organic matter (blocking P sorption sites and increasing organic P pool), 3) and by P fertilization (increasing size of total P pool).

Tomato Suffering from P deficiency


Low available phosphorus is best diagnosed by soil and plant tissue testing. Visual inspection of plants may also be used to identify P deficiencies; a common symptom is purpling or reddening of leaves.

Corn suffering from P deficiency
By Alandmanson [CC0], from Wikimedia Commons


Below is a short summary of various management practices. For a full list of additional resources click here.  

Increasing Soil pH
Liming may increase plant available P by altering mineral surface charge, reducing the affinity of mineral surfaces for P binding.2-3 Liming application rates vary depending on soil acidity, but soils with pH <5 need in excess of 5 tons of lime per ha to bring the soil to the optimum pH.4-5

See section on acidity for additional resources

Increasing soil organic matter
Soil organic matter can improve plant available phosphorus by decreasing the P binding capacity of the soil and providing organic sources of P.

See section on low organic matter for additional resources.

Applying phosphate fertilizers:
Use of phosphate fertilizers will increase total soil P and at least in the near term, increase available P.

  • Phosphate fertilization can be achieved with both inorganic and organic fertilizers.
  • Rock Phosphate is an important P fertilizer in many parts of the world.
  • It is also important to consider other plant nutrient needs when fertilizing.

Additional Resources:

Lime Application:

Increasing Soil Organic Carbon:

Phosphorus Fertilization Strategies:

Further Information


  1. Rasmussen, C.; Matsuyama, N.; Dahlgren, R. A.; Southard, R. J.; Brauer, N., Soil genesis and mineral transformation across an environmental gradient on andesitic lahar. Soil Science Society of America Journal 2007, 71 (1), 225-237.
  2. Kosmulski, M., Surface charging and points of zero charge. CRC press: 2009.
  3.  Parks, G. A., The isoelectric points of solid oxides, solid hydroxides, and aqueous hydroxo complex systems. Chem. Rev. 1965, 65 (2), 177-198.
  4. DCR, V., Virginia Nutrient Management Standards and Criteria. Richmond, VA. 2015.
  5. Margenot, A. J.; Singh, B. R.; Rao, I. M.; Sommer, R., Phosphorus fertilization and management in soils of Sub-Saharan Africa. Soil Phosphorus, CRC Press, Boca Raton 2016, 151-208.