Soil Phosporous Tips

Soil Tips on Phosphorous

I receive a regular enewsletter from the lab I send soil tests to. It’s my regular fix of technical stuff to do with soils, testing, fertilisers and all things horticultural.

Here is some info on Phosphorous I thought the more technically hungry gardener may be interested in...

Phosphorus (P) compounds are highly reactive and tend to bind to other chemicals. Although your soil might have lots of P present, no more than 1% is in a soluble form that plant roots can take up.

To make P available to your plants, plan for warm. moist soils with plenty of organic matter. The pH needs to be pH 5.5-7.2 (remember 6.4 is ideal). See the guys at right doing a simple soil test for pH?

Encourage lots of beneficial microbes. Some forms of highly soluble P fertiliser like monoammonium phosphate [MAP], undergo chemical reactions with the soil minerals and other chemicals, and are easily absorbed by microorganisms.

Microorganisms: When you add a lot of organic matter low in nitrogen, soil microorganisms (including bacteria and fungi) take up all the available N as they multiply on the new source of carbon. They also take up all the available P but release it back to the soil for easy plant uptake as they die. This process is called mineralisation.

Mycorrhizae: Plant roots are assisted in their uptake of P by miccorhizae “fungal plant roots”. Particular types of fungi invade plant roots, but also grow out into the soil. The fungi benefit from carbohydrates supplied by the plants, and the plants benefit from the superior foraging ability of the fungi. The fungi use enzymes to extract P that the roots can’t get at.

Image from: http://gardenofeaden.blogspot.com /2009/05/what-are-mycorrhizal-fungi.html

(Linda: You see how improving the organic matter component and the life in your soil can improve the available phosphorous too.)

This is an abridged and adapted version of the Fertile Minds enewsletter from Sydney Environmental and Soil Laboratory

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