How early N fertiliser reduces the cost of summer drought

Many cereal growers will be looking to front-load their nitrogen fertiliser applications this spring after last summer’s heatwave was blamed for limited uptate of the nutrient, which hit yields.

Earlier nitrogen is key to promote leaf production and growth rates as well as influencing tillering and final ear numbers – something that is fixed by the time crops reach GS31, which generally occurs in April.

Mark Tucker, agronomy manager at fertiliser group Yara, says growers can’t predict the weather, but can plan to encourage early growth and ensure they get enough crop biomass even though last year’s cold, wet spring led to a late start to fertiliser applications.

“Applying a bigger proportion of the total nitrogen amount earlier in the programme is a management consideration if drought conditions are expected, as well as if urea is the primary source of nitrogen fertiliser,” he says.

See also: Light land cereal grower always plans for summer drought

Early nitrogen

Importantly, the first 100kg/ha of nitrogen applied to any crop gives a 12:1 return on investment, which compares very favourably to the marginal 2:1 return from the last 50kg, so it really pays to get the start of the fertiliser regime correct.

“It’s interesting to note that in Germany they always use 100kg/ha as the first dressing,” Mr Tucker says.

He believes 70kg/ha of nitrogen is a better figure for the first application to UK wheat crops, which he accepts is higher than the standard practice of 40-50kg/ha, with a target timing of late February.

“There were many who wished they had put more on early last year. That was tricky to do – it’s worth remembering that the cold, wet spring of 2018 delayed the start of applications on many farms,” he adds. 

Swanton Morley Farms

Simon Brock

Simon Brock

Dereham monitor farmer Simon Brock of Swanton Morley Farms starts his nitrogen planning by doing a soil nitrogen supply (SNS) calculation, letting his Gatekeeper software take care of the maths.

Using field-specific information on previous cropping, manure use, soil type and rainfall, the program tells him how much nitrogen is already going to be supplied to the crop – so he can then make the necessary adjustments to his fertiliser strategy according to yield expectations.

In most years, he aims for about 220kg/ha of nitrogen for his winter wheat, but as he also makes good use of Nutri-Bio on the farm’s oilseed rape stubbles, he has to adjust the total applied in line with the analysed nutrient content of the biosolid.

“It’s all recorded, as we farm in a nitrate vulnerable zone. As well as the Nutri-Bio, we also apply pig muck ahead of sugar beet, so we keep track of everything on spreadsheets,” he says.

As a rule of thumb, he applies 100kg/ha of nitrogen in the first two splits, but is wondering whether he may need to adjust that in 2019 to take account of dry conditions.

“The unknown at this stage is whether to put more on early, to avoid a repeat of 2018, when the lack of rain meant some nitrogen fertiliser sat on the soil surface and wasn’t taken up by the plant,” he adds.

Both solid and liquid fertiliser are used by the business, with liquids preferred for their greater spreading accuracy and solids having a role on the contract-run farms and for later nitrogen applications, as well as to take some of the pressure off the sprayer.

Sulphur is included with most nitrogen applications, with the aim of supplying 45kg/ha of  sulfur trioxide to the wheats.

On oilseed rape, Mr Brock uses a green area index (GAI) calculation based on measuring the crop’s canopy in early spring.

“We know that for each unit of index, 50kg/ha of nitrogen is required. So it is a good way of measuring how much the crop has already taken up, as well as how much more it is likely to need,” he says.

He works on applying 180kg/ha of nitrogen to his rapeseed crops, which gives average yields of 3.9t/ha. The optimum canopy size has a GAI of 3.5, which works out at 175kg/ha of nitrogen.

Danger of overapplication

Only farms that are confident that their nitrogen use efficiency is consistent should use yield to determine the crops’ nitrogen requirement, or else there is a danger they will overapply. 

“It’s how RB209 works now, but we think seasonal conditions have a huge influence and it’s better to err on the side of caution,” he says.

Mr Tucker recommends aiming for a total of 180kg/ha of nitrogen on wheat, with 70kg/ha going on at the start, with leaf testing and crop monitoring then helping to refine the next two splits.

“With more farms adopting practices such as cover crops now, they should be reducing their reliance on bagged fertiliser and coming down from the 220kg/ha average,” he says.

Applying liquid nitrogen to field

© Tim Scrivener

Organic matter

A longer-term view to nutrient planning can be helpful if greater consistency and resilience is needed in the system, says independent soil expert Neil Fuller, who stresses that influencing the organic matter content of soil can shift the availability of nutrients.

“Organic matter does more than improve a soil’s water-holding capacity. It can help with nutrient management too,” he says.

A number of measures can be employed to build soil organic matter, including the use of manures, composts and digestate, growing cover crops, incorporating residues and using techniques such as undersowing.

“Some 70% of arable soils have an organic matter content of below 3.4% and we’re seeing a decline in soil organic carbon every year. So these measures can really help,” he says.

A black oats cover crop, for example, has been shown to supply 20-40kg of nitrogen for the following crop and has given a 0.45-0.85t/ha yield uplift in the next spring barley crop.

“There’s no quick fix for soils and every year is different. On top of that, there’s more interest in biological products that help keep soil microbes active, which can be useful, and nitrification inhibition is potentially going to make a comeback with the government’s Clear Air Strategy,” he says.

New versions of N Tester launched

Yara is launching two new versions of its hand-held leaf nitrogen measurement tool, the N Tester, this month.

Developed for use with the company’s Irix nitrogen management app, the testers can be used to take quick and easy readings in a growing crop to establish its nitrogen status, before giving an instant nitrogen fertiliser recommendation.

A Bluetooth version and a clip-on tester are available, with the former considered to have slightly greater accuracy because of the latter’s reliance on a phone camera.

As such, they can be used for on-the-spot recommendations, as well as for tracking the crop’s nitrogen status and responding to seasonal variation, explains Yara’s Mark Tucker.

“The Irix app can be downloaded for free and put into immediate use on oilseed rape crops. For wheat, we are looking for a group of interested farmers to test the system this year, before we decide on payments terms,” he says.

Existing N Tester users will see subtle differences in the new gadgets, such as a smaller shape, he adds, but otherwise they are identical in terms of measuring the chlorophyll content of selected leaves in order to come up with a fertiliser recommendation. 

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