A guide to getting the most from fertiliser

Yes, in principle, growers would be well advised to apply fertilisers early as the mineralisation in the soil is likely to be lower if they’ve been waterlogged for much of the winter. This is because there will be a nutrient availability lag as the microbial activity gradually increases more slowly than it otherwise would do. This is caveated by the condition of the soil. If further heavy rainfall is expected, though tempting, applications made on frosts is not advisable.

Q2: How much early fertiliser should go on at this time? Same as in normal years, or more or less? Assuming with such high winter rainfall there is little or no residual N in the soil but what about P and K levels?

In terms of nitrogen, the only way to determine an accurate recommendation is to do an N-Min Test (typical cost £50-70) before any nitrogen applications. The high rainfall may mean that there is less available than you might expect since less will have been mineralised by microorganisms and more may have leached out of the soil than usual. In terms of phosphorus (P) and potassium (K), things become a little more complex – it’s all down to CEC (cation exchange capacity).

K is strongly held so less likely to leach but it does leach a little. In previous wet winters (2019 being the notable example), we saw a 6% reduction in the available K in soil samples tested across the UK. Phosphate is more tightly held than potash so logic suggests that it won’t leach, and it doesn’t. What it does do is wash off. Where you’ve seen heavy soil erosion after rainfall you will have lost considerable amounts of P. My advice is to focus on P levels – it will aid rooting where it has been compromised and should be placed below the seed (spring drilling) to encourage further rooting.

To get the best nutrient use efficiency on farm, you need to be putting fertiliser on the right place, at the right time and at the right rate. The interim excess winter rainfall (EWR) data is now available which covers the rainfall from October 2023 to January 2024. EWR reflects the amount of rainfall the land receives after the soil profile becomes fully wetted in the autumn (field capacity) and before the end of drainage in the spring. It has an important influence on the amount of nitrate leached and, thus, the nitrogen availability to a crop. This shows that the whole of Scotland is already in the highest EWC categoryfor bare soil, winter oilseed rape, winter barley and winter wheat.

This data needs to be considered when planning nitrogen applications and reviewing your nutrient management plan based on the Scottish technical notes. Timing of your first nitrogen dose this year is going to be critical and a bigger dose of early nitrogen can help to increase tillering. But be aware that this can increase disease pressure e.g. septoria. This needs to be considered when planning your fungicide programme.

Rooting can be severely compromised following periods of heavy rain and waterlogging, and this will impact on nutrient uptake. Therefore, if conditions allow, get a product on to stimulate rooting before your T0 spray can be beneficial. Peak P demand for cereals is at tillering so it needs to be available to the crop for the peak demand. K peak demand comes later at grain fill. A better root system will also help to improve yields.

Sulphate and nitrate are similar in terms of soil behaviour so sulphur could be added as a foliar treatment with the T0 spray for example. Those who have applied polysulphate or elemental sulphur as opposed to ammonium sulphate will be especially vulnerable this spring so should certainly be considering a foliar feed.

To get the best nutrient use efficiency on farm, you need to be putting on fertiliser on the right place, at the right time and at the right rate

Q3: If farmers have access to liquid fertilisers should they use solid or liquid fertilisers for this early dressing and, if so, why?

I don’t think which you use matters. Both liquid and solid forms of nitrogen are absorbed by the plants’ roots and so the process is the same for each. Growers planning to use granular urea though (protected or not) may see a lag in availability compared to other years as the microbial action to convert this to ammonium and nitrate nitrogen will be slower.

Q4: What is the point at which winter sown crops should be ripped up and resown?

This is going to have to be considered on a farm and individual field basis. If you are concerned about your winter sown crops, please consult with your agronomist/ adviser to review each field to make a decision on whether to rip up and resow.

Each farm will be different in terms of expectations. If the patches are confined solely to headlands, then one might consider bringing the cropped area down and reducing the variable costs. But where fields are patchy generally, consideration must be made to the lower grain prices and lower margins. Adding further variable costs could be a non-starter but this must be the grower’s decision.

Q5: What about trace elements – will they also be low and should early applications be considered?

Proactive measuring of trace elements will be important this spring due to the wet conditions and poor crop rooting. Tissue testing can be used to measure what the plant has already up taken. Laboratories typically analyse plant tissue for nutrients by measuring their concentrations in the dry matter and your results will show which nutrients are low, at target, or high. It is important to tissue test before nutrition deficiency is seen so the nutrition can be applied before the plant is deficient. Balanced nutrition can also help with plants’ natural defences and yield so can have added benefits.

Boron OSR and manganese can be put on cereal crops. Mn is normally manganese sulphate (15% manganese) so will help with the S requirement too.