ARCHIVE: Fertiliser Manual (RB209)

Wheat, Autumn and Early Winter sown – Nitrogen


  SNS Index
  0 1 2 3 4 5 6
  kg N/ha
Light sand soils 160 130 100 70 40 0-40 0-40
Shallow soils 280 240 210 180 140 80 0-40
Medium soils 250 220 190 160 120 60 0-40
Deep Clay soils 250 220 190 160 120 60 0-40
Deep Silty soils 220 190 160 130 100 40 0-40
Organic soils       120 80 40-80 0-40
Peat           0-60

Nitrogen

There is no requirement for seedbed nitrogen.

Depending on the total nitrogen requirement and crop development, it will often be appropriate to apply nitrogen at the following timings.

  • Less than 120 kg N/ha:
    Apply all the recommended amount as a single dressing by early stem extension but not before early April.
  • Over 120 kg N/ha:
    Apply about 40 kg N/ha between mid-February and mid-March except where
    • There is a low risk of take-all and
    • Shoot numbers are very high. Well-tillered crops do not need nitrogen at this stage.
      Crops with too many tillers will be prone to lodging and higher disease levels.

The balance of the application should be applied in one or two dressings during early stem extension. Where more than 120 kg N/ha remains to be applied, half should be applied at the start of stem extension (not before April), and half at least 2 weeks later (not after early May).

Yield variation and use of grain nitrogen concentration

Research has shown that the main causes of yield variation between fields (soil type, rotational position, sowing date or variety) are not associated with variations in the economic rate of nitrogen fertiliser.

Farm nitrogen strategies for wheat should be assessed periodically using information on grain nitrogen concentration. This is a better guide than yield to indicate whether nitrogen fertiliser use is correct. Where there is a consistent trend of low grain %N over several years then nitrogen rates should be increased. On the other hand, when yields are consistently small, it is difficult to justify the amounts of nitrogen shown in the table without good supporting evidence (e.g. from grain %N). Grain %N at the economic optimum rate of nitrogen is about 1.9% N (100% dry matter basis) for feed wheat and 2.1% nitrogen for breadmaking wheat. Where concentrations in yields from a number of adjacent fields are consistently above or below these values during several years, nitrogen fertiliser application rates should be adjusted down or up by 30 kg N/ha per 0.1% difference in grain %N.

To convert grain %protein to grain %N, divide by 5.7. Both N and protein are both reported on a 100% dry matter basis.

The effect of economic changes on nitrogen rates

The recommendations in the tables for wheat and barley are based on a breakeven ratio of 5.0 (cost of fertiliser nitrogen as £/kg N divided by value of grain as £/kg) (see page 32). If the price of nitrogen or the price of grain changes, use the table below to decide on an amount to add to or subtract from the fertiliser nitrogen application.

 

Fertiliser N
content (%)

Fertiliser Cost (£/tonne PRODUCT)
Ammonium Nitrate 34.5% £138 £207 £276 £345 £414 £483
Ureaa 46.0% £184 £276 £368 £460 £552 £644
Urea-Ammonium Nitrate liquida 28.0% £112 £168 £224 £280 £336 £392
Cost of Fertiliser Nitrogen £/kg N £0.40 £0.60 £0.80 £1.00 £1.20 £1.40
Change to recommended N for all Cereals (kg N/ha)
Grain sale price (£/tonne) 50 -30 -60 -80 -100 -110 -130
  75 0 -30 -50 -70 -80 -90
  100 10 -10 -30 -40 -60 -70
  125 20 0 -10 -30 -40 -50
  150 30 10 0 -20 -30 -40
  175 40 20 0 -10 -20 -30
  200 40 30 10 0 -10 -20
  225 40 30 20 10 0 -10
  250 50 30 20 10 0 -10
  275 50 40 30 20 10 0

a. See notes on efficiency of use of different kinds of applied nitrogen page 48

Crops grown for breadmaking

In some circumstances, an application of nitrogen in addition to that recommended above may be economically worthwhile to boost the grain protein concentration. Typically an application of an extra 60 kg N/ha will increase grain protein by 1.1%. Application of soil-applied additional nitrogen during stem extension may give a small yield increase as well as an increase in grain protein. Application as a foliar urea spray during, but no later than, milky ripe stage will result in a larger increase in grain protein content but cannot be expected to increase yield.

Don’t forget to deduct nutrients applied as organic manures (see Section 2)

 

ADLib logo Content provided by the Agricultural Document Library
© University of Hertfordshire, 2011