Understanding Phosphorus Up-Take

Phosphorus is often recognised as being important early on for crop and pasture establishment and root growth, mostly due to its role in photosynthesis and growth in both shoots and roots. However the need for phosphorus doesn’t stop after establishment – adequate phosphorus is important for growth and development at all stages of the plants (or animals) life. 

Thirty percent of soluble phosphorus products such as single super and MAP have shown in University trials to lock up within two weeks of application. Also when phosphorus is applied in a soluble form the soil becomes quickly saturated and the phosphorus will
begin to react and become insoluble or
locked up.

Rhonda Daly, founder and owner of YLAD Living Soils said that the other option for phosphorus fertilisers is soft rock phosphate, which is a slow release, colloidal form. This means that phosphorus won’t saturate the soil solution, but is able to replenish soluble phosphorus as it is taken up by the plants. This is the key to long term phosphorus nutrition because the phosphorus won’t lock up.

Typically phosphorus nutrition is thought of as a chemical process, through the mechanisms described above. However, one of the most important considerations for phosphorus nutrition of the plant is the biological aspect. Although phosphorus is taken up directly from solution, there are a number of important biological processes which will increase the amount of phosphorus the plant can access.

Firstly, plants need to be able to explore large areas of soil in order to access more phosphorus in a given time. Therefore it is important to consider the tilth and structure of the soil to allow healthy root growth.

Many plants are also able to form symbiotic relationships with microorganisms to increase phosphorus nutrition. The most important of these in broadacre crops and pastures are the Vesicular-Arbuscular Mycorrhizal (VAM) fungi. This group of organisms colonise inside the plants roots and spread hyphae into the soil. In effect this forms an extension of the plant’s roots and means the plant is able to access phosphorus in a greater area of soil, often several cm out from the root. This also applies to a number of other nutrients such as Zinc and Copper. In return the VAM are fed with sugars from the plant.

Since VAM are dependent on the relationship with the plant for survival this can lead to poor VAM populations in soils which are over fertilised. This is exacerbated by the often toxic effect of soluble phosphorus on VAM, as well as other farm operations such as cultivation.

Long fallows and crops which do not form relationships with VAM (eg. Canola) can also reduce VAM populations in agricultural soils.

Because of the negative effect industrial farming practices have on VAM populations it can often be beneficial to inoculate with VAM fungi. The inoculum can be applied as a seed dressing prior to sowing to ensure it is present near the growing roots. This is an economical way to improve the phosphorus efficiency of your farming system and promote healthy plant growth.

For more information on incorporating Soft Rock Phosphorus and VAM into your farming system speak to the team at YLAD Living Soils on 1300 811 681

Glenice Buck
Glenice Buck

PH: 0417077386

Glenice is a landscape designer, horticulturist, garden writer and consulting arborist based in Young but she also works on projects throughout country NSW including Sydney. Whenever the opportunity presents itself, Glenice enjoys visiting famous gardens, parks and nurseries around Australia and throughout the world. She is the principal of Glenice Buck Designs.

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