Maximum Yield Australia/New Zealand July/August 2020 | Page 48

“
PEven if your soil
has high levels of
phosphorus, compacted
soil, herbicide damage,
and root-feeding insects
can decrease root
growth and dramatically
reduce a plant’s ability
to uptake phosphorus.”
Preventing and Treating Deficiencies
Phosphorus content in Australian soil varies considerably, with
the entire continent having naturally low phosphorus content
due to weathering. The amount of phosphorus in the soil is
influenced by many factors, including the material the soil was
derived from, climatic conditions, amount of weathering and
erosion, as well as crop removal and fertilisation.
The best way to prevent a phosphorus deficiency is to test
your soil at a reputable lab and amend it if necessary. Sources
of phosphorus for your garden include manure, bone meal,
rock phosphate, and phosphate fertilisers. Chicken manure is
particularly high in phosphorus.
Phosphorus availability is another important factor to
consider. Just because phosphorus shows up on a soil test
doesn’t mean it is available to your plants. Soil pH, temperature,
moisture, and compaction will affect absorption rates.
Ideal soil pH should be between 6.0-7.0 for maximum
availability. Adding lime will raise the pH of your soil over
time, if needed. Low soil temperature, excessive soil moisture,
and soil compaction will decrease availability.
Root growth can have a major impact on phosphorus uptake.
Because phosphorus is very immobile in soil, it is important
that the plant’s roots can grow through the soil to find the
phosphorus it needs. It is important to consider all factors that
affect root growth if you don’t want to end up with a deficiency.
Even if your soil has high levels of phosphorus, compacted
soil, herbicide damage, and root-feeding insects can decrease
root growth and dramatically reduce a plant’s ability to uptake
phosphorus. The soil environment in early spring, with its
cold temperatures and water-logged soil, can cause roots to
grow slowly. For this reason, many gardeners find that young
seedlings can benefit from extra starter fertilisation when
planting even if phosphorus levels in the soil are high.
Increase Phosphorus Availability
with Beneficial Microbes
Microorganisms are key to making sure your plants
get enough phosphorus. Soil that contains a healthy
population of beneficial bacteria and fungi will promote
strong root growth so there is more surface area for nutrient
uptake. These microbes also break down unavailable
forms of phosphorus into plant available forms.
Phosphate solubilising bacteria (PSB) have been
introduced to the agricultural community as phosphate
biofertiliser and have been proven to improve nutrient
uptake and reduce the use of synthetic fertilisers and
pesticides. Three bacteria strains in particular have
proven beneficial: Pantoea agglomerans, Microbacterium
laevaniformans and Pseudomonas putida. Researchers
at Colorado State University have shown that multiple
strains of bacteria solubilise phosphorus more effectively
than any one strain alone.
You can apply PSB by inoculating seeds before
planting, through fertilisation, and in hydroponic
nutrient solutions. Compost and compost tea are
additional ways to increase microbial communities in
your soil, although if you want the PSB strains, you’ll
need to buy a mycorrhizal inoculant with those specific
strains included.
Phosphorus is essential to healthy, vibrant plants,
and maximum yields. It drives energy production and
storage, which is the foundation of just about all the
chemical reactions and processes throughout a plant’s
lifetime. With these basic techniques, you can guarantee
your garden will always have an available source of
phosphorus and thrive.
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Maximum Yield