AHDB guidance to find optimal fertiliser rate as prices soar

The AHDB has issued new guidance to help growers plan for this season’s nitrogen fertiliser applications, following a sharp increase in fertiliser price.

The current energy crisis has led to unprecedentedly high fertiliser prices well in excess of £600/t, with potential for this to rise further before spring 2022.

The price spike means growers must factor in a new “economic optimum” to their nutrient management plans, as the point at which the value of extra grain produced is not worth the cost of the extra N applied has shifted considerably.

Below, we highlight the latest fertiliser advice for arable crops, according to the current prices and trends for both fertiliser input and cereals and oilseeds output prices.

See also: Four farmers’ plans to cope with soaring fertiliser costs

Economic optimum

Georgina Key, AHDB cereals and oilseeds crop nutrition specialist, says a fall in global fertiliser production has led to dramatic nitrogen fertiliser price hikes.

“Over the past few months, the price rise of fertiliser has outpaced prices for grain and, as such, it is absolutely essential that farmers consider adjusting nitrogen fertiliser applications in the spring to ensure they are still at an economically optimum level.”

Dr Key says the optimum amount of fertiliser a farmer should apply decreases as the price ratio between grain and fertiliser increases.

Current RB209 recommendations were devised for a ratio of 5kg cereal grain to 1kg N and RB209 tables for adjustments extend to an ammonium nitrate price of £483/t.

But with prices of ammonium nitrate reaching £700/t, a two-stage study run by the AHDB and Adas was carried out to identify this new optimum level.

The project aimed to answer the following questions:

  • How much should growers be applying?
  • How much should rates be cut back?
  • And what will the effect on yields be?

Price tables in the RB209 have since been extended to £863/t for ammonium nitrate (£2.50/kg).

Cereal grain and rapeseed prices have also been strong of late, so the tables have been expanded to demonstrate prices of £350/t and £700/t, respectively.

New data

The first stage of the study looked at the three major UK crops: wheat, barley and oilseed rape, which are listed below.

The new data indicates that at a grain price of £200/t, a rise in the ammonium nitrate fertiliser price from £345/t to £690/t would see a reduction in N application of 50kg N/ha.

Similarly, at a rapeseed price of £400/t, the same price rise for N would see a reduction in fertiliser application of 70kg N/ha.

The resulting changes in yield would be -0.36t/ha and – 0.25t/ha, respectively. However, recent increases in oilseed prices to about £500/t have mitigated this oilseed adjustment to -50kg/ha N.

The second part of the study, reporting in January 2022, will consider further arable crops, as well as other aspects of crop nutrition management affected by price increases.

Extended version of table 4.22 in RB209 to embrace current prices and trends for cereals

Source of N

Fertiliser N content

Fertiliser cost

 

(%)

(£/t product)

Ammonium nitrate

34.5%

£173

£259

£345

£431

£518

£604

£690

£776

£863

Urea

46.0%

£230

£345

£460

£575

£690

£805

£920

£1,035

£1,150

Urea-ammonium nitrate liquid

28.0%

£140

£210

£280

£350

£420

£490

£560

£630

£700

Cost of fertiliser nitrogen

£/kg N

£0.50

£0.75

£1.00

£1.25

£1.50

£1.75

£2.00

£2.25

£2.50

Grain sale price

Change to recommendation for all cereals   

 

(£/t)

(kg/ha N)

 

50

-50

-85

-115

-135

-155

-170

-185

-195

-205

 

75

-20

-50

-75

-95

-115

-130

-140

-155

-165

 

100

0

-30

-50

-70

-85

-100

-115

-125

-135

 

125

15

-10

-35

-50

-65

-80

-90

-105

-115

 

150

25

0

-20

-35

-50

-65

-75

-85

-95

 

175

30

10

-10

-25

-40

-50

-60

-70

-80

 

200

35

15

0

-15

-30

-40

-50

-60

-70

 

225

40

25

5

-5

-20

-30

-40

-50

-60

 

250

45

30

15

0

-10

-25

-35

-40

-50

 

275

50

35

20

5

-5

-15

-25

-35

-45

 

300

55

35

25

10

0

-10

-20

-30

-35

 

Extended version of table 4.28 in RB209 to embrace current prices and trends for oilseeds

Source of N

Fertiliser N content

 Fertiliser cost

 

(%)

(£/t product)

Ammonium nitrate

34.5%

£173

£259

£345

£431

£518

£604

£690

£776

£863

Urea

46.0%

£230

£345

£460

£575

£690

£805

£920

£1,035

£1,150

Urea-ammonium nitrate liquid

28.0%

£140

£210

£280

£350

£420

£490

£560

£630

£700

Cost of fertiliser nitrogen

£/kg N

£0.50

£0.75

£1.00

£1.25

£1.50

£1.75

£2.00

£2.25

£2.50

Rapeseed sale price

Change to recommendation for ALL OILSEEDS

 

(£/t)

(kg/ha N)

 

200

0

-40

-70

-90

-110

-120

-130

-150

-160

 

250

20

-20

-50

-70

-80

-100

-110

-120

-130

 

300

40

0

-30

-50

-70

-80

-90

-110

-120

 

350

50

10

-10

-30

-50

-70

-80

-90

-100

 

400

70

30

0

-20

-40

-50

-70

-80

-90

 

450

80

40

10

-10

-30

-40

-60

-70

-80

 

500

90

50

20

0

-20

-30

-50

-60

-70

 

550

90

60

30

10

-10

-20

-40

-50

-60

 

600

100

70

40

20

0

-10

-30

-40

-50

 

650

110

70

50

20

10

-10

-20

-30

-40

 

700

120

80

50

30

10

0

-10

-20

-30

 

Effect on grain yield of adjusting N applied from the optimum at a breakeven price ratio of 5kg grain/kg N for cereals or 2.5kg seed/kg N for oilseeds

 

Cereals

Oilseeds

Reduction in N applied (kg/ha)

Effect on yield (t/ha)

0

0.00

0.00

-10

-0.05

-0.03

-20

-0.12

-0.06

-30

-0.19

-0.09

-40

-0.27

-0.12

-50

-0.36

-0.16

-60

-0.47

-0.21

-70

-0.59

-0.25

-80

-0.72

-0.31

-90

-0.87

-0.37

-100

-1.04

-0.43

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