What’s the minimum Phosphorus rate if you are following a poor crop?

Many growers will be thinking about what to do with Phosphorus (P) fertiliser for their next winter crop. Soil tests are the best indicator of whether a paddock is going to be responsive to P fertiliser.

If your soil tests shows moderate to good levels of P, and yields were low in the previous season, you can usually reduce P fertiliser rates. P is a relatively immobile nutrient in the soil. If not removed in harvested product P tends to remain in the soil. Harvested grain removes 2.5 – 3.0 kg of P for each ton of grain. Around 1 kg of P is removed for each ton of dry matter cut for hay.

Whatever the background soil P situation having some P near the seed at sowing is a reliable way to get seedlings off to a good start. Young plants are less effective at scavenging P from the soil, even when nutrient reserves are present.

The minimum rate at which even distribution of fertiliser can be achieved is 3kg P per hectare. Dropping your P fertiliser rate below 3 kg P per hectare risks setback in the establishment of the crop with reduced early vigour.

This video was recorded in late 2014, but the advice remains current for western Victoria and the south east of South Australia that had a poor season in 2015. Regions that had a reasonable to good season in 2015 will not have the same potential to reduce P fertiliser rates.

Further Information

IPNI
Phosphorus after the dry – experience from the past
Phosphorus – how much can we reduce P
Phosphorus Best Management Practice

GRDC
Dry 2015 could reduce cropping input requirements in 2016
Determining soil nutrient levels a must after the dry of 2015

eXtensionAUS
Phosphorus – Australian Agronomy 2015
What happens to P from crop residues
Deep Phosphorus fertiliser trials in NSW

Acknowledgements
Rob Norton, IPNI, Charlie Walker, Incitec Pivot, Jeff Kraak, Fertilizer Australia

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