Knowing your soil is key to getting the most out of it – Potato Review – Andrew Goodinson

“As the investment you are making by planting potatoes is huge, if the field is not right – for example there have been tight potato rotations and soils are tightly compacted – it may be better to say no.”

The more you know about your soil, the better, and Andrew points out that this is where new technology is a real help. For example, the mySoil app (from the British Geological Survey) and the ADAS soil app can give you some useful information about soil in the local area. “But we all know that you can’t sort a field out in one year – it takes many years of work to improve it; so revisiting the previous crops on the land can give good pointers.”

He points out that knowing what has gone before is easy when growing on your own land but because of land pressures, many growers have to rely on rented land – in which case it is well worth developing a good relationship with the landlord who can help with providing key information about the ground.

“For example, I pay particular attention if there has been maize or sugar beet in the rotation, because of the damage they may have done to the soil, it may need remedial action. If there has been a grass ley, you may well have an increased risk of wireworm, and if potato crops in the rotation have been tight, there may be PCN.”

Knowing where soils are heavier and wetter, can help make decisions on where to plant first and where to leave until later, he adds, noting that while this may be a given for those who have been farming the same land for years, it can be more of a challenge when renting new land.

Testing for organic matter and nutrient availability is a key factor for a successful yield, emphasises Andrew. For more in-depth information, he finds web-based systems such as SOYL and Omnia to be extremely useful. “This puts you in a better place to match the crop’s nutrition requirement and also to take preventive action against PCN if necessary.”

Because of its tendency to bind with other substances in the soil, understanding phosphate (P) availability and the all-important ration between calcium (Ca) and magnesium (Mg) necessary to its uptake, can help drive better decisions on fertiliser, he says .

“In the west we tend to see a lot of soils with high P but low potassium (K), so purchasing a 14:14:21 fertiliser may not be the best option – even if it is on sale at a good price.” In the east soils tend to be higher in K with a lower P, he adds.

Where organic manures are used, he recommends getting a good analysis, as it composition and nutrients can vary, and there are differences between stored and fresh manures.

Every farm storing FYM must have accurate and reliable manure management plans in place, and he recommends a web-based system such as Omnia which makes legislative compliance much easier, but also helps him match applications to soil requirements.

“Bear in mind that if you are using farmyard manure (FYM) from cattle, you need to be sure that they have not been fed stock potatoes, because powdery scab can pass into the manure; or if fed outside it can survive in the soil.”

While applications of FYM or composts help to maintain good soil structure and improve uptake of fertilisers and crop protection chemicals, Andrew prefers soil amendments to be doing elsewhere in the rotation rather than an attempt at a quick fix immediately before potatoes.

He also recommends soil testing for locations of hotspots for pests such as potato cyst nematodes (PCN) and free living nematodes (FLN). “Symptoms of rhizoctonia can easily be confused with FLN damage,” he warns.

Soil type can also impact on PCN activity; they tend to proliferate where water has stood on flooded soils, especially where there is compaction. To minimise risks he suggests looking at ways to ensure prompt runoff of surface water, such as checking field drainage to ensure it is working properly, and ensure a good standard of soil husbandry is kept to.

Andrew notes that potato growers with their own land are increasingly using cover crops to help maintain nutrients in the soil and reduce run-off, a practice which he supports. Cover crops or stubble turnips are being encouraged by some of the processors, too.

However, to get maximum benefits, he stresses the importance of knowing how to manage them, which to some extent also depends on soil type. “Cover crops on heavy soils need to be removed sooner than on lighter soils because of the risk of slugs.”

Nevertheless, he suggests that when destroying them, it is often a good idea to leave some biomass behind as it can help protect soils and make them more resilient.

“If you opt for stubble turnips or oilseed rape which is then grazed off, it is a good idea to remove the livestock before they eat right down to the bare earth, as their feet can cap the soil and seal in wet or dry.”

He cautions, however, that making such an investment in land rented for one year may not be an economically viable solution for growers.

Creating an environment with good tilth is the secret to successful planting, and Andrew emphasises that the secret is to keep the aggregates small enough for good seed to soil contact, but not too fine as heavy rain may cause the soil to slump. However, he finds there is often room for improvement when it comes to cultivations.

“Many farms have a blueprint they follow, for example, destoning, declodding – both of which burn carbon and destroy organic matter (OM) – but there can be an option to reduce the number of passes if soils are suitable. That said, there is no point in missing the destoning if you then have to do two passes with the bed-tiller.”

Many growers still try to cultivate too deeply, he remarks, noting that reducing depth can also reduce costs without affecting yields, recommending that growers seek advice for the particular varieties they grow.

“When, for any reason, seedbed preparation is inadequate, even the best soils will produce inferior crops as uniform sprout emergence and young plant vigour depends on a consistent, firm, porous, moist bed.”

The soil can still be wet and cold at depth when spring-planted crops such as potatoes go in, so he sometimes finds reducing the cultivating depth can be beneficial to reduce clodding.

“Turning the soil still has benefits, there are times that turning the soil can help it warm up more quickly and rain penetrate more easily, but it can also dry out. Remember that once you have planted it normally takes the soil ten days to settle, but if you have forced it, it can slump then the tuber has no room to grow, which may lead to ridge cracks and greening.

There are a number of factors which can cause compaction, he says, including soil type and the structure of soil working elements, water content of the soil, and the load of harvested material on machinery, putting pressure on the soil. Nevertheless, modern large machinery can make a seed bed when conditions are not ideal, he notes.

“It’s important to spend some time setting up your tractors, weight and ballast, as well as making sure you are using optimum tyre pressures.”

If fields are subsoiled, a lot of carbon is lost he points out, adding that subsoiling also reduces the food available for microbes, so when dealing with compaction there are lots of things need to be considered.

“The best tool is spade; so I would always go out and dig a hole and have a look. Good soil management is all about knowing the challenges you have to deal with on a particular soil, as well as being flexible and adapting timing according to the weather at the particular moment.

“Soils are particularly vulnerable in spring, so special care should be taken if possible and give the soil time to breathe before ripping it with steel. If the conditions are not right, then it is better to hold back.”

Top Tips

1. Know your soil type, crops in the rotation and wet/dry patches
2. Avoid over-cultivating or planting too deeply
3. Assess pest load and hotspots
4. Invest in cover crops where possible
5. Test soils for available nutrients and fertilise according to plant needs
6. Avoid travelling on the land when the going is not good