Quality Minimises Risk On-Farm

We see ever more extreme weather conditions, with dry springs being more common than wet ones. If we think of this in particular, dry weather in spring means that crops need to be even more resilient to cope with the lack of moisture. This requires the crop to have a root system that is large and deep enough down the soil profile to access water. Crops get this resilience by maintaining momentum once they start growing again in the spring, which can be at quite low temperatures, 5°C for cereals and oilseed. We can help this with our first fertiliser application, giving the crop the best chance of accessing the nutrients we apply, as it is likely they are growing before you’ve been able to travel on the fields. Fertiliser choice is important at this point because not all nitrogen-containing fertilisers are plant-available straight away.

Nitrates are the most available form for plants to take up immediately, without any conversions needing to occur, therefore ammonium nitrate (AN) products provide immediately available nitrogen to the crop. If we look at urea-based fertilisers they have to undergo a conversion in the soil before they become nitrates and therefore aren’t immediately available to the crop. Depending on soil conditions this can take 6-8 weeks in cold, wet soils and therefore we could really be slowing down the crop momentum; which we really don’t want to do at that key timing in the spring. So if you think that the weather could cause this delay on your land, AN fertilisers are the best choice and are quickest to be plant-available.

The timing is also very important, especially that first application. Yara has independently conducted, long-term trial work where nitrogen rate trials are carried out every year. This enables us to plot the response curve of the different rates of nitrogen. The best response, and therefore return on investment, comes from the first 40-50kg of nitrogen. This first chunk of nitrogen is most efficient and, from both the long-term data and this season’s trials, gives 32kg of grain per kg of nitrogen applied – this equated to 1.2-1.6t/ha increase in yield above the untreated plots. The next 50-60kg isn’t used as efficiently by the plant and gives 15-25kg grain per kilo of nitrogen. As we go further up the nitrogen rates (and the curve) the return on investment isn’t quite as good as you’re getting less kilos of grain per kilo of nitrogen applied. Therefore what this shows is that first 40-50kg of nitrogen is vital and certainly we don’t want to risk affecting this with poor quality, inefficient or delayed applications.

There are some other key factors to consider for the first application timing – P & K. We know that several factors affect the uptake of phosphate in the soil and temperature is quite a key one. As I mentioned before, we want the crop to start growing and not falter at all in the spring, to make sure it is putting on plenty of biomass; which will ultimately become yield. If the soils are cold and wet, which they mostly are coming out of winter, phosphate availability is very low from the soil (<10%). This means that, even if you applied some in the autumn, the crop isn’t able to take it up because it is not available to the crop until soils warm up beyond 8°C. Therefore if we want the crop to access P&K when it can’t access it from the soil, we need a fresh application in the spring, around 35-50kg, to ensure there are available nutrients when the crop requires them. Again, independent trials results show that, from fresh applications of P&K in the spring you can get a 0.3t/ha yield increase. Also we are increasing overall nutrient use efficiency of other nutrients by having P&K readily available.

Another consideration with all fertilisers is the spreader settings. If you are using a blend you have to set the spreader up for the nitrogen fraction because it is the most important nutrient. However this compromises whatever other nutrients are in the blend, as they would have different weights and densities to the nitrogen, and therefore this brings in variation of all the other elements. Another potential problem with blends is the number of landing sites of the nutrients. With a compound fertiliser, where all the nutrients are in the same granule/prill, the analysis that is on the bag is in every landing site. If we think of a blend, there is usually different amounts of each nutrient, if we think of 20-10-10 as an example, there is half as much P and K as there is nitrogen. This means the number of landing sites for the P&K are greatly reduced and quite variable. Some areas won’t get any P or K, and we know that P doesn’t move very far once it is in the soil, so we are adding in risk of deficiency there. This can’t happen with compounds as they contain all the nutrients and can’t segregate in the hopper either. This might sound like it is on a small scale and that the majority of the field will have some P and K, but actually there are up to 10 times less landing sites, when you think of that over a whole field it will soon cause large-scale variation to that growing crop, which will carry through to harvest.

Another consideration if thinking about using straight N, P, K and S currently is the cost of fuel; whilst applying straights might appear cheaper, when you add in the fuel costs of the extra passes it makes it more expensive than applying an NPKS compound fertiliser.

Another consideration in farming today are emissions. Urea has come under scrutiny in the fact that it emits ammonia in to the atmosphere; which is linked to environmental and human health issues. This is why the government released the Clean Air Strategy a few years ago and why they are bringing in policies to try and reduce ammonia emissions from urea-based fertilisers. The problem with urea is the fact that volatilisation occurs when urea hydrolyses, this is when ammonia is released into the atmosphere. It is made worse in warm, moist conditions, especially if there is also a drying wind. Urease inhibitors can be used to reduce emissions from urea but the levels are still higher than ammonium nitrate and CAN. Therefore the easiest way to reduce ammonia losses is to use an AN-based fertiliser.

In summary, think about potential issues you’ll have in the spring and buy products that can help minimise the risks. Remember small amount of fresh P&K in the spring, which is most easily and economically applied as an NPKS compound, are required at that first application timing. Make sure you set up the spreader correctly for accurate and efficient use of your fertiliser investment and finally think of the environmental impact of your fertiliser choice in terms of ammonia emissions.