by Bill Crabtree, Agronomist
Nitrogen use efficiency is critical when supply is tight. Bill Crabtree outlines six practical strategies to help WA grain growers do more with less N this season.
Six Ways to Improve Nitrogen Use Efficiency This Season
With restricted nitrogen supply this year it is wise to consider how you can drop perhaps 30% of your program. Several ways to do this are:
- Grow more legume
- Cut back on canola (keep it for the real weedy paddocks)
- Band more nitrogen at seeding – keep it away from the inter-row
- Dissolve some of your urea in water to apply it foliar – like with UAN
- Cut back on how much you apply – the first dose is best dollar value
- Plant some early Mohawk in late March to scavenge for N
Grow more legume
A recent 4Farmers podcast with Mark Seymour gives good insight into which legumes will best suit your farm.
Some hot tips from Mark include – lupins are obviously best on sands, peas are the most adaptable to all soils and wind erosion concerns are less with no sheep and choppers on headers, faba beans are best when conditions are likely to be quite wet, vetches are adaptable as a brown manure, lentils work with better textured soils and no subsoil acidity. And don’t forget sub-clovers!
Cut back on canola
Canola is a high nitrogen user, so pulling this back 30% will leave more N for your cereals. Or try and grow the canola on a legume stubble.
Band more N at seeding
Many trials have shown that banding N is usually more efficient than topdressing it. Further, keeping the N away from the interrow means that there is less N that can be gobbled up by soil microbes near the organic matter. Keeping the N away from bacteria means that other bacteria will jump into the interrow that fix N out of the air and leave the applied N for the crop.
When these free-living N fixing bacteria die – a few weeks later – they release their bodies to the soil and let go of the N they fixed. By allowing N fixing bacteria to grow in the interrow (by not applying fertiliser N) you gain more N for your whole system than you applied.
Dissolve urea and apply it to the leaves
This is what many farmers on the Eyre Peninsula of South Australia do. They use some propane to help the dissolving process. You can only get 21 kg N to dissolve in 100 L of water. This way it can be used like UAN.
A good part of liquid urea that lands on the leaf goes straight into the plant. Further, the plant uses less energy to convert urea into amino acids in the leaf than it does to convert nitrate that comes from the roots to the leaf. This makes N more efficient. The urea applied to the leaf, in a canopy, also means less N gets tied up in the surface organic matter.
Cut back on applied N
The graph here illustrates a range of seasons you might get (and yield potential) or the range of N response curves.
In every season, the best bang for your buck is the first dose of N. This graph suggests that if you get 20-30 units of N on then you will capture a good part of the crop’s yield potential.
Plant early to scavenge more N
Early sown crops are very efficient at scavenging N before it slips through the soil profile on leaching rains. So, if you get a chance to plant in late March with a winter wheat variety like Mohawk consider giving it a go.
The addition of Aquifer will help achieve good even crop establishment which also helps with a healthy root system, water repellence and a dry start to the year.
Want to talk through your options before seeding? Call the 4Farmers team on 9356 5445.
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