Potato advice blog

Increasing marketable potato yield with biostimulant

Biostimulant products trigger natural plant processes that enhance nutrient use efficiency. Improved plant growth and abiotic stress tolerance help the plants to remain vigorous in hostile growing conditions so the farmer can generate better yield and quality.

YaraVita BIOTRAC is a biostimulant that, when applied to crops in combination with mineral nutrients, triggers the processes that enhance nutrient uptake and efficiency, improve plant growth, boost tolerance to abiotic stress and increase yield beyond the effects of mineral nutrients. Their role in alleviating abiotic stress is seen as crucial in protecting crops from the full effects of drought and extreme temperatures.

Ghent University, Belgium, evaluated the effect of two different application rates of YaraVita Biotrac on the yield and quality of potatoes grown under field conditions in 2018. The applications were applied 50 days and 82 days post-planting and the harvest data was then compared to the untreated control.

YaraVita BIOTRAC increased the premium marketable grade (>50mm) by 8.5% and 11.8% for the 1 L/ha and 2 L/ha treatments respectively, compared to the untreated control. These results give us confidence that YaraVita BIOTRAC has an important role in growing premium quality potato crops profitably.

See the potato biostimulant trial results

Calcium crucial for good quality potatoes

Calcium is a crucial nutrient when growing potatoes as it plays an important role in quality parameters. Potatoes need calcium to strengthen tuber skin; providing better resistance to many diseases (black scurf, silver scurf and common and powdery scab) and also a better skin finish.  Therefore calcium (along with other nutrients) can make the difference between selling the crop pre-pack or as ware; that price differential, therefore, making up for the cost of the application.

Calcium deficiency also causes internal rust spot so it’s essential to apply calcium at the right time. That time is tuber initiation. This is when an application of calcium to the potato crop is essential to flush the developing tuber with soluble calcium.

However, it’s not only the timing of calcium that needs to be right but also the source of calcium that is being applied. There is a misconception sometimes that liming materials will contain and provide enough calcium for the crop, but many liming materials are Calcium Carbonate based. This means that they are not very water-soluble and, consequently, the calcium is not freely available to the potato crop through the growing season.

For example Lime is calcium carbonate – it requires 66,000 litres of water to dissolve 1kg of calcium carbonate; which means it would take a long time to become plant-available and definitely not within the season where it’s required. YaraLiva Tropicote only requires 1 litre of water to dissolve 1kg calcium nitrate; which means it has high calcium solubility and therefore is available to the plant when it’s needed.

Calcium is a very important nutrient when growing potatoes and it is key to get the correct timing and correct product to see the best results.

Benefits of potato fertiliser placement at planting

With planting about to start in the next few weeks this is maybe a good time to reflect on the benefits of fertiliser placement.

There are yield benefits from placing fertiliser at planting rather than broadcasting and from using compounds rather than straights as well as from optimising calcium, phosphate and zinc nutrition; here are some of the highlights from recent trials

Consistent yield benefit from placement of fertiliser at planting

Over the years Yara has carried out a large number of trials on the application of fertilizer to the potato crop, focusing on placement at planting. This has consistently given yield benefits, averaging 10.8% over 18 years of work. With continued legislation driving more efficient use of fertilizers such practices will become even more important. Applying fertilizer to the planted areas and not broadcast all over must be more acceptable from an environmental risk point of view. 

Application accuracy is a key focus for Yara, particularly in the potato sector. YaraMila compounds can bring benefits over straights for the delivery of nutrients to the crop, with a 7.8% yield increase over straights in a long-term trial at Hanninghof Research Centre. 

Maintain a green leaf canopy for longer to increase tuber size and yield

Recently Yara has also looked at the benefits of supplementing the basal nitrogen applications with foliar treatments. Additional nitrogen can be supplied using dilute applications of Chafer Nufol to help maintain a green leaf canopy and increase tuber size and yield . When compared with soil applied top-dressings significant improvements in nitrogen utilisation can be achieved, as we saw from this year results with an 8.3% yield increase. 

Other trial work carried out by Yara includes the benefits of calcium for tuber quality, foliar phosphate applications to improve tuber numbers and tuber size and just recently, the impact of zinc, where in 2014 a 1l/ha application of YaraVita Zintrac 700 lead to a 5% yield increase.

Boost boron and calcium levels in late season brassicas

Late season vegetable brassica crops are susceptible to several quality issues which can reduce marketable yield. Boosting levels of calcium and boron in these crops via nutrition will prevent many of these quality issues and so can increase profitability.

Boron has several key roles in plants which include cell wall biosynthesis, carbohydrate and protein metabolism, cell division/elongation and also root and shoot growing points. Boron is the only nutrient which, when in short supply, can accelerate physiological processes instead of reducing them and therefore abnormal growth can occur.

Calcium deficiency is often seen in late season brassica including tip burn on cabbage or glassiness of cauliflower where sections of the curd may be brown or discoloured. This is directly related to a lack of calcium within the cell walls, meaning that they aren’t strong enough and when cell expansion takes place they collapse and necrosis occurs.

Once calcium is incorporated into cell walls it can’t be redistributed therefore it is important to have sufficient supply as new cells develop. As mentioned already, calcium is integral to cell walls and give the cells, particularly the skin, strength. Therefore a sufficient supply will help ensure the crop has a good appearance as well as helping against both biotic and abiotic damage.

Yara brassica trials have also highlighted the synergy between calcium and boron, improving the uptake of each nutrient and improving the control of associated disorders, not only in brassicas but also in other crops showing a response to calcium and boron such as potatoes.

Boosting levels of calcium and boron in brassica vegetable nutrition will prevent many of the quality issues, increasing marketable yield and so increasing profitability. Boron and calcium work together to improve plant strength by reinforcing cell walls so reducing the effects of nutritional disorders such as tip burn in cauliflower, hollow stems or internal browning.

YaraLiva NITRABOR contains a balanced combination of soluble nitrate nitrogen, calcium and boron that can be safely applied to green crops right up to harvest without fear of scorch to enhance both the quality and marketable yield of vegetable brassicas. There is also a synergistic effect whereby the uptake of nitrate, unlike ammonium forms of nitrogen, can increase the uptake of calcium.

Although we are now in the closed period for NVZs, applications to brassicas are still permitted. Applications of manufactured nitrogen fertilisers are allowed on vegetable brassica crops under NVZ regulations during closed periods up to a maximum of 100kgN (with 50kg max every 4 weeks).

Yara recommendations, to comply with NVZ regulations are to apply YaraLiva NITRABOR at up to 320kg/ha every four weeks up to harvest.

Why a healthy canopy is essential for quality potatoes

A healthy potato canopy is important in ensuring we maximise the plant’s ability to fill the ‘tuber sink’ thus producing as many marketable potatoes as possible, and improving profitability. Removing both biotic and abiotic stress will help to ensure a healthy, well-functioning potato canopy.

The ideal potato crop uses very limited amounts of the sugars to maintain its canopy, thus partitioning the majority into the tubers. When considering how to minimise the energy that is required to maintain a canopy, we need to focus on how we reduce the plant’s respiration to a minimum. A plant’s respiration rate will increase when it comes under stress,which reduces the amount of sugar produced during photosynthesis that is available for tuber bulking. It is essential to manage these stresses out of the production system and for abiotic stress such as temperature or drought relief can be aided by the use of biostimulants.

Nutrient deficiencies can be monitored through plant leaf analysis. Data from Yara Analytical laboratories reveals some of the key nutrient deficiencies found in potatoes to be phosphate, potassium and magnesium. Phosphate is of particular importance due to its role in the transport of the sugars from the leaf down to the ‘bulking’ tubers. The transport mechanism is an energy demanding process and the chemical energy is stored by the plant in the phosphate based molecule ‘ATP’. Magnesium, the central component of chlorophyll (leaf greenness), clearly has an important role in keeping the leaf canopy greener for longer. Potassium helps the plant regulate water and nutrient movement from roots, through the plant, to the leaves. Water movement itself is also a necessity in the transport of sucrose down to the ‘bulking’ tubers.

By removing both biotic and abiotic stress you will ensure a healthy, well-functioning potato canopy. This will give the best chance of maximising the important ‘tuber bulking’ period, and result in high, marketable potato yields.

Recommended action: During full canopy cover, two applications of YaraVita Magphos K @ 5 l/ha + YaraVita Biotrac @ 3 l/ha, with 14 days between applications.

Are your potatoes getting enough calcium?

Calcium is a vital nutrient for potatoes and most aspects of tuber quality can be improved by having a sufficient supply of calcium during growth. It is required in the crop for the maintenance of cell walls, healthy leaf and tuber development.

Calcium deficiency is widely known as internal rust spot - a physiological internal defect in which small brown spots, due to cell death, appear in the tuber. This is directly related to a lack of calcium within the cell walls, meaning that they aren’t strong enough and when cell expansion takes place they collapse and necrosis occurs. 

Once calcium is incorporated into cell walls it can’t be redistributed therefore it is important to have a sufficient supply as new cells develop. As mentioned already, calcium is integral to cell walls and give the cells, particularly the skin, strength. Therefore a sufficient supply will help ensure the skin has a good finish as well as helping against physical damage which can occur during harvesting and handling. 

However it’s not only the timing of calcium that needs to be right but also the source of calcium that is being applied.There is a misconception sometimes that liming materials will contain and provide enough calcium for the crop but many liming materials are calcium carbonate based. This means that they aren’t very water soluble and consequently not freely available to the potato crop through the growing season.

As previously mentioned the timing of application to the potato crop is essential to flush the developing tuber with soluble calcium therefore the optimum application period is at tuber initiation. The ideal source of fully soulble calcium is YaraLiva Tropicote which should be applied at tuber innitiation.

Is there a better way of applying phosphate to potatoes?

Following tradition many potato growers continue to apply phosphate using straights such as DAP or MAP but this might not be the best practice.

Phosphate is particularly important for potato establishment and has an important role in the development of shoots and in particular roots and this is why a sufficient supply is key in the early stages of potato crop.   The problem here is that phosphate is relatively immobile in the soil and relies on the roots being able to grow towards it rather than the phosphate moving through the soil towards the roots.  Couple this with the fact that potatoes are a particularly poor rooted crop and in the early stages often struggle to establish an effective root network capable of accessing water and other nutrients and you can see why this is an issue.

There are several ways to improve management of phosphate in potatoes by using YaraMila compound fertilisers rather than more traditional 'straight fertilisers'.

Better timing of P and K applications ensures that the phosphate is applied close to when the plant requires, so limiting the amount that becomes locked up by the soil.  This is favoured by applying P and K as compound fertiliser at or just after planting rather than as separate 'straight' applications prior to planting.

Better distribution of phosphate through the soil profile also helps plant uptake.  The best way to achieve this is to increase the number of fertiliser particles. Traditionally phosphate has been applied as relatively concentrated DAP di-ammonium phosphate, containing 48% P₂O₅ so there are relatively few concentrated particles. Similarly if the phosphate is applied in a blended fertiliser using DAP or MAP there is still the same problem of the phosphate being contained in relatively few particles resulting in a an uneven distribution of nutrient through the soil. 

However, if phosphate is applied as a compound fertiliser such as YaraMila Actyva S instead then every single prill or granule contains all nutrients and at a concentration of 14%  P₂O₅  there will be approximately three times as many particles.  This leads to more even spreading and a more effective distribution of nutrients throughout the soil which inturn leads to more even crop growth and increased yield

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Potato nutrient requirements

The potato crop requires potassium in large quantities, 50% more, in fact, than nitrogen. A 38.5t/ha crop can remove more than 120kg/ha of nitrogen whereas it can remove over 200kg/ha of potassium. Both of these macronutrients are important throughout vegetative growth, tuber formation and bulking.

Nitrogen is important for leaf and tuber growth and is recycled from lead to the tuber during bulking, the same can be said for potassium. When thinking of potassium then as you can see from the removal values that it is key for high yields and maintaining tuber integrity.

Phosphate is also required in relatively large quantities during early growth due to its importance in root and shoot development and tuber set but also later on in the season for bulking.

Calcium is a crucial nutrient  as it plays a role in important quality parameters. Potatoes need calcium to strengthen the skins of the tubers; providing better resistance to many diseases (black scurf, silver scurf and common and powdery scab) and also a better skin finish.   Calcium deficiency also causes internal rust spot so it’s essential to apply calcium at the right time but also ensure the correct source of calcium is used. For example, liming materials won’t supply plant-available calcium to the crop therefore it won’t supply sufficient supply to meet the demand.

Magnesium is important during tuber bulking where it plays a major role in maintaining tuber quality and is therefore a key nutrient.

Micronutrients are also important to ensure the crop has all it needs to produce a good, quality yield. Zinc and manganese are key to help the crop’s defence against powdery and common scab as well as maintaining skin finish.

Why is sulphur so important for potatoes? Yield or common scab control

It is well-known that sulphur deposition has decreased to almost nothing meaning no more sulphur is deposited on the land – sulphur applications are therefore a must.

When thinking about sulphur on potatoes there is, of course, the important relationship between sulphur and nitrogen. Nitrogen can’t be taken up by the plant or utilised as efficiently if there is a deficiency in sulphur. The N:S of uptake per tonne of yield in potatoes is 8.5 which is similar to cereal crops and trials have shown up to 15% yield increases from 40-75kg SO₃ sulphur applications to potatoes.

However, does sulphur have another important part to play in the potato crop?

Quality is very important when growing potatoes, especially their skin finish, therefore common scab can be a real issue. Common scab is more prevalent on high pH soils (alkaline) therefore the theory is that acidifying the area around the tuber will help control common scab. Sulphur helps to acidify the soil therefore applications of sulphur should help with control.

Sounds simple then – apply sulphur and you won’t get common scab…unfortunately it’s not as easy as that. Trials work Yara did showed that there was no consistent effect of applying sulphur for common scab control at the usual 40-75 kg SO₃. Further work on higher rates, 150kg SO₃ +, showed more promise, but even at these very high rates there was only a marginal effect on the scab.

So, when thinking of sulphur on potatoes it should be to increase yields and nitrogen use efficiency and not common scab control. The most effective method of controlling common scab is therefore still irrigation, ensuring the moisture reaches the depth of the tubers.

Boron deficiency in brassicas

All brassicas have a high requirement for boron and deficiency can cause poor crop establishment together with increased plant losses and ultimately reduced yield.

Boron has several key roles in plants which include cell wall biosynthesis, carbohydrate and protein metabolism, cell division/elongation and also root and shoot growing points. 

Root and shoot development are obviously key to establishing the plant early on to ensure that it gets off to the best start to help combat pests and diseases. Also during this period the plant is growing very rapidly and therefore having a sufficient amount of boron present is essential to keep the root and shoot development rate optimum. 

Boron is the only nutrient which, when in short supply, can accelerate physiological processes instead of reduce them and therefore abnormal growth can occur. Symptoms of boron deficiency often start on the younger leaves of the plant and they appear crinkled, deformed and brittle. Necrotic patches may appear at the leaf margins and the plants may appear stunted. Stems can also be affected with hollow lesions occurring and splitting of the stems. Some of these symptoms can be made worse by sandy, alkaline soils low in organic matter as well as high levels of calcium present. 

Vegetable Brassicas require boron in quite large amounts where it helps control nutritional disorders such as tip burn and hollow heart. Find further information on the symptoms and causes of Boron Deficiency in Vegetable Brassicas

Yara brassica trials have also highlighted the synergy between calcium and boron, improving the uptake of each nutrient and improving the control of associated disorders, not only in brassicas but also in other crops showing a response to calcium and boron such as potatoes. 

YaraLiva NITRABOR contains a balanced combination of soluble nitrate nitrogen, calcium and boron that can be safely applied to green crops right up to harvest without fear of scorch to enhance both the quality and marketable yield of vegetable brassicas.