Written by George Hepburn, Soil Fertility Consultant at Aiva Fertiliser
Nutrient use efficiency is a bugbear of mine. As an industry I think we do a pretty bad job of using so called ‘fertilisers’.
This is a table that I have seen many times, it might be a bit harsh on Nitrogen at 30% but even if we take the top end figure it still means that we are losing 50% of our applied N. Not only are we not utilising it, the other 50% is causing major damage to our soils and waterways.
This article is about Nitrogen but really it starts with Phosphate. If we thought we were doing a bad job with Nitrogen then look at the P figures – 15-20%. We have known for many years that TSP is poor form of phosphate for availability. It gets locked up very quickly with the dominant cat-ions within your soil, some say within hours. Yes it will build your soil reserves but you probably have plenty in that fraction what you really want is available P.
This come back to soil structure, another well used chart:
50% of your soil should be air and water, it is a farmers primary job (IMO) to manage this air and water. You can have very little effect on the mineral composition of your soil and maybe increase the OM by 1% over 10 years if you are farming really well. However, you can have a huge influence over the air and water in your soil.
Drainage is where it all starts, if you can get he water moving through the soil it allows the air in. Air is key to beneficial biology that we want to encourage. The phosphate solubilising bacteria are aerobic. Like me and you they need a house (structure), water (in the right amounts, anything can be poison just depends on the dose rate) warmth (10 C is where it really starts happening) and food (carbon). Give them these in the right balance and they will thrive, releasing phosphate to the plant in the form it wants.
The available Phosphate not only stimulates root growth but also gives the plant the energy it needs to do some fairly heavy lifting.
Soils are not always in the right state at this time of year to release P (cold, wet etc) so a foliar Phosphate is a nice option. We like to recommend a foliar P with some traces before we start to apply N, as with an active root system, the right trace elements and some metabolic energy in place, we stand to uptake and utilise more of the applied N as we have our house in order!
Onto applying Nitrogen, there is no point talking about the different forms of soil applied N as you will have what you have. But in general more splits are better. If you are looking to reduce fungicides then 180 kg/ha is the most you should be applying (alongside the requisite amount of S) ideally 150 kg/ha or less.
In the East where we are getting major drought issues, then the final 25% should be in the form of a balanced foliar N. Meaning we take the pressure of the soil when its processes are starting to shut down and get it directly into the plant with efficiency of 90% plus. It also means we can add Mg, K, traces, seaweed, aminos, fish hydrolysate and carbon with it.