Navigating nitrogen: Crop considerations

Fertiliser prices are on the rise, once again. Bek Hirstman, AHDB Agronomy and Environment Manager, discusses some of our products, tools and services to navigate nutrient needs for cereals and oilseeds.

Renewed geopolitical tensions and volatility in global energy markets have pushed up nitrogen costs. This is adding pressure to margins that are already tight.

It’s only natural that growers are asking: ‘Do I really need to spend this much on nitrogen?’.

Nitrogen is important for its role in crop growth, yield formation and grain quality. However, when costs escalate, it becomes even clearer that maximum rates don’t always deliver maximum returns.

The most profitable strategy is usually about using nitrogen more efficiently, rather than applying more of it.

The last time fertiliser prices spiked in 2022, we developed a nitrogen adjustment calculator. This tool is based on the nitrogen recommendations for cereals and oilseeds in Section 4 of the AHDB Nutrient Management Guide (RB209).

Accounting for fertiliser costs and grain prices, the tool calculates the economic optimum nitrogen rate.

At higher fertiliser prices, the tool often suggests lowering the farm’s typical rate (and vice versa).

Last month, we started publishing weekly fertiliser price updates (instead of monthly data) to aid decision-making.

At the end of March, the price of imported ammonium nitrate (34.5% N) was £522/t with new crop wheat at £182/t.

In this scenario, RB209 and the calculator could suggest reducing nitrogen rates by around 35 kg/ha.

With fertiliser prices high and milling wheat premiums pressured, farmers are also asking: ‘Does it pay to chase protein?’.

Certainly, the economics of late nitrogen are far from guaranteed.

RB209 guidance is clear that protein response is highly variable, influenced by the yield potential, season (including the weather during grain fill) and premiums.

Where milling contracts are secure and realistic protein targets are achievable, late nitrogen may be justified.

Without that certainty, many crops may be better managed for yield and margin, rather than risking additional spend for an uncertain return.

Understanding and maximising nitrogen use efficiency (NUE) is a key focus at our Strategic Cereal Farms. It can offset yield losses associated with reduced fertiliser rates.

For example, Strategic Cereal Farm East is using data on economic optimum nitrogen rates.

So far, the work shows that overall field yields align with historical performance.

However, the economic optimum varied substantially within fields, which were split into smaller nutrient management zones (as mapped by technologies, including an N-sensor).

This is where the story takes an interesting twist.

For instance, a relatively poor-performing area saw no yield benefit in applying nitrogen above 150 kg/ha. A more productive area in the same field showed yield increases up to 275 kg/ha.

Of course, the economic optimum would be below these two rates.

In fact, an application of 110 kg N/ha yielded only 0.25 t/ha less than the 150 kg/ha rate in the poorly performing zone, but rates could be cut by around 100 kg N/ha in the higher-performing zone, while still only sacrificing a similar yield (0.25 t/ha). 

This clearly shows the benefit of understanding how crops respond to nitrogen across and within fields.

It can take a lot of graft to get to grips with NUE across fields, but it will count for little if soil health is neglected.

The right physical, chemical and biological conditions are essential for crops to take up all nutrients (macro and micro) effectively.

Focusing solely on nitrogen is a bit like trying to cook chips by adding more oil to the pan but never turning on the heat. The input is there, but the conditions needed for it to work are not.

A deficiency in any nutrient will often restrict overall nutrient uptake and utilisation.

Earlier this year, we ran Smart Nutrition Roadshow events to explore the various factors behind successful crop nutrition.

Compaction, poor drainage, low organic matter or nutrient imbalances can all restrict root growth and limit nutrient uptake.

The events also highlighted the critical role of soil pH, which influences the availability of all nutrients.

When fertiliser prices are high, it’s tempting to concentrate spend on the nutrient known to have the biggest influence on yield and cut back elsewhere.

But balanced nutrition is king (and RB209 is queen) to ensure that every ounce of costly input is put to good use.