Nitrogen is important in fuelling growth and providing high yields. It is largely needed during leaf formation and then for tuber growth and yield, when it ensures optimal photosynthate production in the leaves.
Nitrogen fed at an early stage of crop development will help build the overall size of the leaf canopy. At later stages of growth, nitrogen use helps maintain the greenness of the canopy and maximize yield.
In temperate climates, an excess supply of nitrogen at later stages of growth will keep the crop growing, preventing it from reaching maturity. It may also reduce starch content, reducing processing potato crop quality.
An excess supply of nitrogen at later stages of growth may also reduce dry matter content, affecting quality.
Where high levels of nitrogen are needed, advantages can be obtained from splitting N applications. Trials with a three way split increased yields by 12% compared to where all the nitrogen was applied in one go.
As around 60 % of the total N is taken up before tuberization, a standard dry applied program may use 2/3 of the total N at planting and the remaining 1/3 at around tuber initiation or as several foliar sprays with the blight treatments.
The total amount of nitrogen supplied will vary according to the length of time the canopy needs to be maintained and any potential losses such as leaching. Optimum total N rates vary with soil type and previous cropping history.
Where there are apparent yield responses to very high applications (>300 kg/ha), checks should be made for losses due to leaching.
Potatoes are very responsive to NPK at planting. Balancing nutrition in such a manner – often with magnesium and sulfur applied at the same time - ensures a good start for the potato crop.
Over-use of early N can lead to excessive vegetative growth at the expense of tuber formation.
|Nitrogen at potato growth stages|
|Planting||Early growth and dry matter|
|Post planting||Split applications to reduce losses|
|Ridging and hilling||Second split application|
|Bulking||Maintain tuber growth|