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)