ARCHIVE: Fertiliser Manual (RB209)

Potatoes – Nitrogen


The recommendations below provide general guidance only. Because of the very wide range of varietal characteristics and quality requirements for different market outlets, guidance from a FACTS Qualified Adviser should be used when making decisions for specific crops.

The SNS Index below should be used together with the anticipated length of growing season and variety group to determine the appropriate range of nitrogen rates.

  SNS Index
Length of growing seasona and variety groupb 0 and 1 2, 3 and 4 5 and 6
  kg N/ha
<60 days – Variety group 1 100-140 70-110 40-60
  – Variety group 2 80-120 50-80 0-40
  – Variety group 3 60-100 40-70 0-40
  – Variety group 4 N/A N/A N/A
60-90 days – Variety group 1 160-210 130-160 90-120
  – Variety group 2 100-160 60-120 40-80
  – Variety group 3 60-140 40-100 0-60
  – Variety group 4 40-80 20-40 0-40
90-120 days – Variety group 1 220-270 190-120 150-180
  – Variety group 2 150-220 110-160 80-120
  – Variety group 3 110-180 80-100 40-60
  – Variety group 4 80-140 40-60 0-40
>120 days – Variety group 1 N/A N/A N/A
  – Variety group 2 190-250 150-180 120-150
  – Variety group 3 150-210 120-140 80-100
  – Variety group 4 100-180 60-80 20-40

 

N/A= Not Applicable
a. 50% emergence to haulm death
b. Examples of varieties to in each variety group are as follows:

 

Group 1 Short haulm longevity
(Determinate varieties)

Accord, Estima, Maris Bard, Rocket and Premiere.

Group 2 Medium haulm longevity
(Partially determinate varieties)
Atlantic, Lady Rosetta, Marfona, Maris Peer, Nadine, Saxon, Shepody and Wilja.
Group 3 Long haulm longevity
(Indeterminate varieties)
Maincrop varieties such as Desiree, Fianna, Hermes, King Edward, Maris Piper, Rooster, Russet Burbank, Pentland Dell, Pentland Squire and Saturna.
Group 4 Very long haulm longevity Cara and Markies.

 

Nitrogen increases yield by prolonging haulm life. It has no effect on tuber numbers and consequently, where it gives an increase in yield, the mean tuber size will be greater.

Factors that may influence the nitrogen rate

The recommendations assume that loss of ground cover should begin close to the time of defoliation and harvest. If crops are planted later than intended and the defoliation date remains unaltered, this will reduce the length of the growing season which will justify a reduction in the nitrogen application rate.

Excess applications of nitrogen can:

  • Increase haulm size, delay natural senescence and create difficulties with desiccation.
  • Delay achievement of skin set.
  • Affect achievement of target dry matter levels.

Timing of nitrogen application

If top dressing is planned for management reasons or to reduce the risk of leaching for crops grown on light sand and shallow soils, apply about two-thirds of the nitrogen recommendation in the seedbed and the remainder shortly after emergence.

For other crops, apply all of the nitrogen recommendation in the seedbed.

The effect of irrigation

There is no difference in the nitrogen recommendation between irrigated crops and those which are not irrigated

Placement of nitrogen in bed systems

The same recommendations should be used for bed as well as ridge and furrow systems, and where nitrogen fertiliser is placed.

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

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