A NEW protocol for estimating the determinacy – how crops utilise fertilisers – of potato varieties will be released in the next few months and will be added to the AHDB’s Nutrient Management Guide (RB209).

This should help breeders and those involved in variety development, save time and money when producing nitrogen recommendations for new varieties.

From this, growers and agronomists will gain more accurate nitrogen/determinacy groupings for both new and existing cultivars, and thus fine-tune the N rates applied to crops.

A key component of nitrogen fertiliser recommendations, as used in the AHDB Nutrient Management Guide, is the nitrogen (determinacy) group. These are based on four groups: Group 1 (very determinate) through to Group 4 (very indeterminate).

Potato varieties such as Accord, Estima and Innovator are part of Group 1 as they cease leaf production after the first (or indeed second or third flowers) but when compared with indeterminate varieties, they will produce fewer leaves.

In contrast, varieties classified as group 4 determinacy, for example Cara, Markies and Royal, continue to produce leaves and flowers until they are curtailed by shorter days and frost.

“It is essential to know the grouping of your variety, in order to calculate the correct nitrogen recommendations,” pointed out Alice Sin, an AHDB resource management scientist.

Research conducted by AHDB and NIAB, with help from Greenvale AP and Cygnet PB, has resulted in the new protocols.

The determinacy of potato varieties was studied using four methods – plant ground cover, main axis nodes and harvest index measure - both fresh and dry weight.

The accepted approach was to count main-axis nodes on the potato plant – a robust, quick, cheap and non-destructive method – but by combining the four criteria much more robust data was obtained.

Other methods of determining N rates for different varieties groups relied on carrying out several costly nitrogen response experiments. As a result, many varieties could have been mis-allocated, resulting in applying more or less N than needed.

Ms Sin continued: “Some of the previous N rates groupings were based on opinion and casual field observation, so we are delighted to now publish a protocol which is evidence-based as it will offer a great help to the whole industry.

“These updated groupings, including newer varieties from the top 50 varieties grown in GB, will be incorporated in the 2021 revision of the AHDB Nutrient Management Guide, Section 5.”

The protocol is currently being trialled by Meijer Seed Potato, the results of which will be published on the AHDB website in the coming months. Max Tärneberg, Meijer sales rep for the east of the UK, said it was a good fit for his company, as it already has multiple trial sites across the UK.

“This year, we are going to include the node counting methodology alongside our normal assessments in line with the new protocol. We already have a good understanding of the N groupings of all but our very newest varieties, which will help us in calibrating this new system.

“If we find it to be accurate against our current understanding, then this could have huge implications for how we successfully market newer varieties. We could have an N grouping for a variety before it even gets a name.”

Mr Tärneberg recognised the need for a new protocol: “In a broader industry sense, this could bring the N groupings of many varieties right up to date. If more accurate N recommendations are more readily available for our industry, then we could be looking at significant savings”.

The new protocol will be included in the training courses provided by technical training company, Artis, and will also be discussed during workshops which will be organised at AHDB’s Strategic Potato Farms (SPot) including Scotland’s new SPot farm, seed potato supplier, Milton of Mathers Farm, situated in St Cyrus, Montrose.