Big N fertiliser savings in milling wheat with polysulphate

Producing nearly 9t/ha of wheat and hitting the Group 1 milling specification from just 164kg/ha of nitrogen fertiliser is possible, according to trials.

This was despite the crop being drilled in late October and enduring a challenging season.

Agrii’s Green Horizons team has been investigating how best to improve the nutrient use of milling wheat in a series of trials at Agrii’s Stow Long Technology Centre.

See also: Hybrid rye: The benefits of growing it and how to do it well

The 2020/21 trials involved a mixture of second, third, fourth, fifth and sixth crops of Skyfall in a continuous wheat block, following permanent grass and wildflower mixtures.

Crops were sown at 375 seeds/sq m in the late October and received identical crop protection and micro-nutrition programmes.

Liquid nitrogen rates and timing were varied, together with key early season macro-nutrient applications on the high pH, high calcium clay ground, indexing 2+ for both potassium and magnesium.

Wanting to really challenge the breadmaking system, trial co-ordinator David Felce deliberately set the standard nitrogen rate at 214 kg/ha, well below what would normally be applied.  

“Then we cut it to just 164kg/ha in some treatments,” he says.

The high calcium soil at Stow Longa is known for locking up potassium and magnesium, so he varied both nutrients while keeping sulphur rates the same.

Spring 2021

“The wet conditions meant very backward crops coming out of the winter and prevented us getting our first fertiliser on until early April, after which it turned cold and dry,” says Mr Felce.

To help the crop cope with this, he included 14kg/ha of foliar nitrogen ahead of the final pre-flag leaf N application.

Despite the challenging spring, crops across the 1ha block averaged 8.35t/ha at 12.1% protein. As expected, the second wheat performed best at over 8.5t/ha, while the fourth and fifth wheats were just under 8t/ha.

Across all the crops, the standard fertiliser programme involved an initial application of 100kg/ha of polysulphate followed by the 150kg/ha N at the first split and 50kg/ha pre-flag leaf.

It yielded an average 8.47t/ha at 12.0% protein for a gross margin of £803/ha.

Dropping the final 50kg/ha of N, while keeping the rest of the programme the same, reduced the average yield slightly to 8.29t/ha, while lifting the protein content to 12.4%.

The net result was a margin increase of just under £30/ha at 2021 costs and crop values.

The real value from reduced nitrogen usage, however, came from a more typical quality wheat approach with N applications back-loaded.

Putting on 60kg/ha at the first split and 90kg/ha on the final one lifted the average yield to 8.9t/ha, with a protein of 13.7% and gross margin of £1,030/ha.

“Given the state in which the crop came out of the winter it would have been a prime candidate for early N if we could have got on the ground,” Mr Felce says.

However, he adds that the unusually cold, dry April did them a big favour by holding back crop development. “This particularly helped our back-loaded nitrogen regime.”

Fertiliser efficiency

applying liquid nitrogen

Applying liquid nitrogen to winter wheat © Tim Scrivener

The end result was that crops performed well, despite receiving 100kg/ha less nitrogen than conventional wisdom suggests.

To have increased the yield by nearly 0.5t and boosted the protein content by over 1.5% while cutting N use by 50kg/ha is hugely encouraging, he says. Especially so, in margins at current nitrogen prices.

Also impressive is the nitrogen-use efficiency over 98% for the best-performing regime, against 67% in the standard programme.

While the timing of the N as well as the season was clearly important in this performance, the trial showed other elements of the fertiliser programme were equally, if not more, crucial here.

The difference in performance at the low nitrogen rate where no spring polysulphate was applied is especially revealing, says Mr Felce.

Compared with the almost identical reduced N with polysulphate regime, yields were down by almost 0.33t, protein content by 1.5%, nitrogen-use efficiency by 13% and gross margin by almost exactly £200/ha to just £643/ha.

“This underlines that improving nitrogen-use efficiency is as much about balancing the other major nutrients the crop needs as it is about manipulating N type or timing,” says Mr Felce.

High calcium soil

“Stow Longa soils may have good potassium and magnesium indexes, as well as decent organic matters, but our analyses show they also have well over 6,000 ppm of calcium, which seriously limits the availability of these nutrients.”

Under these circumstances, he says the 14kg/ha of potash and 6kg/ha of magnesium provided by the polysulphate made all the difference to the efficiency with which the crops were able to use the nitrogen.

“The importance of achieving a good balance between available calcium, potash and magnesium was clear where we replaced the polysulphate with an NKS fertiliser (treatment 5).

Despite providing much more potash than the equivalent back-loaded N programme and 50kg/ha more N, the average yield was noticeably lower at 8.65t/ha, as was the nitrogen-use efficiency at 78% and gross margin at £901/ha.

“These results really underline the opportunities we have for using significantly less nitrogen than most of us have become used to, even for the most demanding crops in the most difficult seasons,” concludes Mr Felce. 

“But for the greatest value, this clearly needs to be combined with the right balance of other important nutrients for the particular soil conditions.”

Stow Longa wheat nutrition trial 2020/21

Fertiliser treatments *







Nitrogen use efficiency (%)

Gross margin

1: Standard N/polysulphate






2: Reduced N/ polysulphate






3: Reduced N/back-loaded/ polysulphate






4: Reduced N/no polysulphate






5: Standard/back-loaded/NKS







1. Standard N: polysulphate (100kg/ha); liquid N (150kg/ha); foliar N (14kg/ha); liquid N (50kg/ha)

2. Reduced N; polysulphate (100kg/ha); liquid N (150kg/ha; foliar N (14kg/ha)

3. N/back-loaded: polysulphate (100kg/ha); liquid N (60kg/ha); foliar N (14kg/ha); liquid N (90kg/ha)

4. Reduced N/no polysulphate: Liquid N (150kg/ha) Foliar N (14kg/ha)

5. Standard N/back-loaded/NKS: NKS (343kg/ha); liquid N (60kg/ha): foliar N (14kg/ha); liquid N (80kg/ha)


Need a contractor?

Find one now