Potato Review

22 POTATO REVIEW JANUARY 2022 SOIL PREPARATION 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.” Where organic manures are used, he recommends getting a good analysis, as its 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. Knowing the pests in your soil 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. Cover crops before potatoes 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 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. Keeping cultivations to a minimum 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.” 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 “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.” A bee on phacelia.