An obsession with timing and good nutrition has resulted in well grown, consistent, even potato crop canopies across a number of varieties, reports Heather Briggs, after crop walking with specialist potato agronomist Andy Alexander.
The tour included varieties destined for the processing and crisping sectors.
The soil typically varied between clay and sand, and some of the crops are irrigated (rain-gun or trickle irrigation). Andy’s fertiliser strategy is to apply 60 per cent at planting, with the remaining 40 per cent going on just before tuber initiation, so the plant uses the nutrients to develop tubers rather than over-develop canopies.
This year there are 47hectares (140 acres) of Shepody being grown for a major processor, and they are looking particularly well. Planted on an old airfield in mid-March in light soils using cut seed, they then got a little behind because soils were slow in warming up.
“This variety is usually sparse in tuber numbers, so I usually up the seed rate by 10 per cent to get a good return per hectare of planted area,” explains Andy, who sits on the NFU Potato Forum.
Despite a slow start, the crops have caught up and developed well and were in flower at the beginning of the second week of July. The area missed out on the heavy June downpours, so the dry soils are currently being irrigated.
A sample dig showed excellent tuber numbers of the right size per stem, although, as yet still a little immature. Although the aim is to start lifting at the end of the July, the proportion of dry matter will be a key factor on deciding the lifting date, he says.
Knowing your variety is key to getting the most from it, says Andy. “Some with great culinary properties are agronomically more challenging. For example, Innovator is an excellent processing variety which provides the customer with the right shape for processing and a flesh which comes out well after storage.”
Planted on 22nd March, this year’s crop of Innovator is developing a little ahead of the Shepody, the canopy is well developed and evenly grown, and it began losing its flowers in the first few days of July.
A sample provided lines of four uniform tubers per stem. “Lovely,” says Andy. “It is a good even crop with great potential. It is grown as a second early in this area of Norfolk. However, as the variety has shallow roots which tend to move laterally if they come across any compaction, it tends to do better in lighter soils. This is because it less able to penetrate downwards to scavenge for water and nutrients at lower levels than some other varieties.
“As a result, Innovator can often really benefit from a foliar feed rather than extra N applied in the seed-bed. It is a fickle variety, but it makes a very good product and this year’s crop can be expected to live up to its reputation.”
Earlier crisper Lady Claire was planted in May on land which previously had been grazed. This crop is not being irrigated, but thanks to the good soil structure helping hold on to moisture, it also had an even canopy, although this one had not yet closed.
“We may hold on for harvesting as this crop is destined for delivery in July 2020. Lady Claire is very good in storage because it can withstand lower temperatures than Saturna, thanks to its sugar stability. However, it does not provide record yields, although it fits in with niche market crispers.
“To get the best return, it needs to be stored until at least May or June the following year, when most other varieties are already out of store, and prices start to lift. The challenge, however, will be working with the customer to decide on a sprout suppressant strategy as CIPC is being withdrawn (see below).
Sitting pretty alongside Lady Claire was Lady Rosetta, and the sample showed it to be well on target with three stems with five tubers each. “We have good stems which is converting into a good population, which is in part due to the uniform canopies delivering uniform samples.”
Late-maturing Markies has received less nitrogen (N) this year, partly because the variety needs to develop higher dry matter (DM) but also because it is late maturing and needs six weeks to achieve skin-set.
“This variety generally needs little N, however, as we have cut it back still further, it may affect yield, but the real challenge this year is the loss of the desiccant Diquat, so we want the crop to stop growing earlier.”
A sample of the ever-popular Maris Piper produced three stems and tubers with consistently good conformation close to the stems. “This is important as it helps to reduce losses from greening,” adds Andy. This year’s crop of Piper is being grown on Grade 1 soil, with no PCN and the grower’s aim is to maintain the soil quality, he notes.
The variety still has a great deal going for it; growers understand how to grow it to get the most from it and it is also a good investment from a marketing point of view, he says. “We know it is a variety you have to irrigate and is susceptible to herbicide scorch from some of the residual herbicides. However, if you have a bumper yield and have more potatoes than contracted, it is easier to sell than some lesser-known varieties.”
The tall, even canopy of Russet Burbank stood out for its ability to take maximum benefit of the sun’s radiation. The sample showed beautifully consistent 90mm tubers growing on three stems.
“This crop is growing on good fertile soil with irrigation, and every care is taken to ensure that everything is done at the right time and in the right place, and this crop has not been stressed. As a result, we can expect both quality and yield,” said Andy.
Local Norfolk-grown seed potatoes
Growers are now able to source seed potatoes locally in Norfolk, as B&C Farming is now producing seed varieties for some of the large processors.
“This is very useful as it means it is easier to see them when they are growing, then inspect them for the number of eyes, which of course translates into stem number and potential tuber numbers. It also means we get delivery exactly when we want!”
More research on nutrition needed
“As an industry, we could still do better plant nutrition,” says Andy, noting that in some cases, potato crops may use as little as 10 per cent of applied phosphate, he reveals. “We may be missing a trick, so we need more research on some of the basics of nutrition, especially trace elements and how they can become locked up in the soils.”
Part of the problem is that soils interact differently, so results are not consistent. This could be partly due to the influence of the previous crop, he said. He advocates tissue testing to understand whether the plant is suffering from any particular deficiencies which could hit yield and/or quality.
“We have seen cases where crops had received sufficient levels of phosphate below the root but they still look anaemic. This can be because either the roots are shallow – such as with Innovator – or the phosphate is locked up. The best way to address this is to identify the problem with tissue testing, and then use a foliar feed accordingly.”
Nutrition can also help plants become more tolerant to some of the common pests found in soils, he adds. “If you were able to double the root hair length you could also significantly increase the nutrition and water they would be able to scavenge, making it possible for them to grow away from some of the pest damage.”
While a constant temperature remains key to good storage, crops for processing and crisping destined for long-term storage will be hit hard with the withdrawal of sprout suppressant CIPC, says Andy.
“One of the problems is that for processing we are not able to store at the low temperatures used for the fresh-pack sector. As a result, we have to look more carefully at the tools that we still have in the box, and those include ethylene and spearmint. We may be able to do more with ethylene than current thinking suggests, so we need to keep working on it.
“There are a lot of people who are concerned about any possible taint from using Spearmint, but as it is a volatile substance, after three or four weeks it is really difficult to detect any residual smell or taste,” he says.
He is also disappointed with recent regulations concerning maleic hydrazide, insisting that when properly used, there should be no issues at all. “It could be that there are some areas of registration which are missing and need to be addressed.”
The trick of effective trickle irrigation
We need to take steps to use water more effectively, says Andy. Last year he found trickle performed better than rain-guns on fields near the coast. He points out that one of the challenges of growing potatoes so close to the North Sea is the wind, which affects uniformity of irrigation from rain-guns. Nevertheless, he insists, trickle irrigation also needs to be done properly to be effective. “The trick with trickle is to start soon enough, before you get much of a water deficit, so that you can then maintain it with a low volume of water.
“There have been occasions where I have had to irrigate by another means to wet the soil first, and then use trickle to keep it moist.”
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