To say this season so far has been difficult for some is an understatement. When faced with so much variation in crops it is important to use nutrition to manipulate the crops as best you can in order to get the most from what you have.
To say this season so far has been difficult for some is an understatement. With so much variation in crops out there, managing nitrogen applications this spring could be challenging.
A lot of nitrogen and other nutrients that were in the soil will have been lost
Cold, wet or waterlogged soils mean the levels of mineralisation are likely to be very low this season. When there is excess water in soil pores that is usually filled with air conditions turn anaerobic. When there is no oxygen available in the soil nitrogen is lost through denitrification. When you team this with the amount of excess rain we’ve had, a lot of nitrogen and other nutrients that were in the soil will have been lost as well.
Phosphate will be particularly important this spring
Another nutrient affected by cold soil temperatures is phosphate. Crops start to grow with soils at 5°C however phosphate is still unavailable at these kinds of temperatures therefore the crop can soon start to struggle. We want to keep the crop’s growth momentum going as soon as it starts to grow therefore an application of fresh P, even at the higher indices, will be beneficial when it is unavailable from the soil. Due to the conditions we’ve had, the root system of crops is likely to be sub-optimal at best, damaged at worst, therefore phosphate is particularly important this spring. We want to make sure the seminal roots start to grow well. Waterlogging will have encouraged the growth of adventitious roots. These are usually shallow and therefore limited in nutrient uptake. We now need to spur on the roots to grow deeper to access any nutrients available deeper in the soil.
In the meantime, we need to give the crop as much help with nutrition as possible while it might be struggling. An NPKS product would be ideal at this first timing to give the nitrogen and sulphur which go hand-in-hand in terms of uptake and utilisation, but in addition providing fresh P (and K) for the important root growth.
First nitrogen applications will need adjusting
What does this mean for first nitrogen applications this spring? This depends on when it was drilled, whether it is normal or backwards, or indeed if it is about to be drilled.
If we take a normal cereal crop, we recommend continuing as usual with 70-80kg N of an NPKS product at the first application in mid-end of February (so long as conditions are conducive). This gives the crop the best chance of building the foundation of biomass before the cut-off date in mid-March. Again, if you have a normal crop of rape then go ahead with around 80kg in mid-late February.
If we are looking at a late drilled, backwards cereal crop then the advice will differ. Split your first application to put 30-40 kg N on ASAP then follow up with another 30-40kg N at the end of February. This will help a struggling crop access immediately available nitrogen, if using ammonium nitrate. As mentioned, a compound NPKS product is best due to phosphate availability. The fresh P will help the potentially small, damaged root systems caused by waterlogged conditions. Often people ask about applying urea at this time, however this year in particular this could be risky. Urea won’t have the same effect as AN as it takes 10 days – 6 weeks to hydrolyse and convert into plant-available ammonium and nitrate. Therefore, if your crops are looking ‘sick’ then opt for immediately available ammonium nitrate.
For a backwards OSR crop then a similar approach can be taken, 40 kg N (again an NPKS product would be ideal) on ASAP and see how the crop reacts. If it starts to pick up and recover, then the remaining 40kgN can be applied at the end of February.
Phosphate will get crops off to a good start
In terms of foliar products at this time of year, then foliar phosphate is a great tool to get crops off to a good start. Foliar P is taken up into the crop a lot more efficiently than solid forms. Applying some foliar P now as soon as you’re able to will spark off the crop’s growth. This then needs to be backed up with your NPKS application very soon afterwards (i.e. same day or shortly after) so that the crop doesn’t run out of steam once you have started the momentum.
Once the crop is heading towards T0 then taking some tissue tests will show if there are any micronutrients that are starting to become low within the crop. If there are these can be rectified with foliar applications. This year in particular will be key for utilising micronutrients, due to lack of availability in the soil and to manipulate the crop at certain key timings.
This spring is going to be difficult, there’s no doubt about it. Be smart about nutrition, and manipulate the crops as best you can, to get the most from what you have.
The following fertilisers are recommended for all crops and supply a combination of either nitrogen and sulphur (N+S) or nitrogen, phosphate, potassium and sulphur depending on requirements in appropriate ratios to allow the ideal timing for application of all nutrients.