Fertilizer International 505 Nov-Dec 2021
30 November 2021
Potato nutrition re-imagined
POTATO CROP NUTRITION
Potato nutrition re-imagined
Yield, quality and profitability are the primary focus for the modern potato grower. But these objectives need to be balanced against the need to reduce the environmental impacts that result from cultivating the world’s fourth-biggest food crop. Fertilizer International talks to David Marks of Levity Crop Science about how its unique approach to product development is helping farmers adopt more sustainable agricultural practices.
Delivering more from less
“Everything we do at Levity has one singular objective: identifying ways in which crop production can be made more sustainable. Of course, that demands better and more efficient use of resources, as well as a reduced environmental impact.”
“But it also means maximising yield and production – we have to get more from less.”
That’s Dr David Marks, founder of UK-based Levity Crop Science. This innovative, R&D-led business develops and markets so-called ‘smart’ or ‘functional’ fertilizers. Levity’s crop nutrient products are, in fact, difficult to categorise, as they combine the attributes of both biostimulants and conventional fertilizers.
Their benefits are, however, more easily understood. Compositionally, the company’s products are designed to boost farm production and profitability, while reducing wasted resources – often the root cause of subsequent environmental problems. These are also the problems for which farming, and farmers, generally take the blame.
“Take nitrogen, for example,” says Dr Marks. “Every potato grower knows how vital nitrogen management is for the growing potato crop. They’ll tweak their N regimes to reflect different end uses, and time their applications to optimise yield and quality.
“Yet many growers would probably be surprised to find out that the crop in their fields is making use of only 25-35 percent of the applied nitrogen fertilizer.”
“Leaching, microbial action and mineralisation can see up to three-quarters of that nitrogen become inaccessible to the crop.”
Dr Marks says the most commonly used forms of nitrogen in agriculture are often determined by availability: “They’re also based on what’s been easiest to secure in large quantities, not necessarily what’s best for the plant.”
It was this kind of supply-driven approach that led Dr Marks to consider how to make better use of nitrogen in the field. By understanding how plants absorb and use different types of nitrogen, Levity has successfully brought to market products that offer much greater nitrogen use efficiency (NUE).
Nitrogen – available in three different forms
Nitrogen is commonly supplied to crops in ammonium form (e.g. urea) or as nitrates (e.g. potassium nitrate, NOP) or as combination of these two forms (e.g. ammonium nitrate, AN). Nitrates can deliver superior yields and quality in arable, fruit and vegetable crops (Fertilizer International 506, p28) – including potatoes (Fertilizer International 506, p56). They generally have a much lower environmental impact relative to urea-based fertilizers as well, due to their ability to avoid volatilisation losses. Their production can also have a lower environmental impact.Nitrates are, however, prone to leaching and have a lower nitrogen content than urea.
There is, however, a third form of plant-available nitrogen – amine urea. This, in stabilised form, is the nitrogen fertilization option favoured by Levity Crop Science.
“Plants can absorb three different types of nitrogen,” explains Dr Marks. “Nitrate, ammonium and amine all result in different responses, and the plant expends different amounts of energy to absorb, transport and utilise each one of them.
“Soil-applied ammonium is quickly converted to nitrate by soil microbes. Yes, the plant can turn it back into ammonium – but it’s an energy-intensive process.”
Plants process nitrates within leaf cell structures called chloroplasts. Transporting it to the chloroplasts uses energy though, as does the generation of the enzymes needed to convert nitrates into amino acids, the building blocks of proteins. In fact, says Dr Marks, it can take 12 times more energy (carbon) to turn nitrate into plant protein than for the same unit of nitrogen absorbed as an amine.
“For protein synthesis, the plant can use both amine and ammonium forms immediately,” notes Dr Marks. “That allows the plant to use its captured and converted solar energy for growth instead, immediately, without any kind of a processing lag. Carbon instead becomes biomass – i.e. yield.”
Because amine and ammonium are both processed in the roots, there’s no energy expended in transport or enzyme generation. The added attraction is that amine in the roots has a positive effect on the production of cytokinin, a plant hormone that triggers reproductive growth: another plus for tuber production.
“Yet many growers would probably be surprised to find out that the crop in their fields is making use of only 25-35 per cent of the applied nitrogen.
Stabilised amine urea (SAN) technology
Levity has focused its efforts on finding a means of delivering amine directly to the plant. It settled on a stabilised form of amine urea. Rather than using polymer coatings, or the urease and bacterial inhibitors preferred by other manufacturers, the company instead developed its own unique approach.
“The problem with inhibitors is that they can affect the mineralisation process. Sometimes that’s favourable, but not always.
“Our stabilised amine urea (SAN) technology – LimiN – relies on forming a cross-linkage between the NH2 amine and a monovalent or divalent cation. This has the effect of making the NH2 form of nitrogen invisible to soil bacteria.
“And by supplying nitrogen as SAN, we give the plant access to a more efficient form of nitrogen. Not only can we apply less nitrogen and achieve the same amount of plant growth, but the nitrogen usage itself is more energy-efficient within the plant.
“Crucially, the amine form also encourages more reproductive growth – the tubers – because it has an effect on the plant’s hormone balance.”
Yield improvements and more
Early field trials of the technology showed that SAN not only increases yield, but, in creating shorter plants with more roots, the crop also demonstrated greater resilience to drought-induced stress and lodging. Greenhouse trials revealed that leaf chlorophyll content increased in the presence of SAN, thus improving the plant’s photosynthetic activity.
Lono, a Levity product that incorporates LimiN technology, has demonstrated yield increases for potato growers around the world. “Exports account for more than 70 percent of Levity’s sales,” reports Dr Marks, “which means we get to prove our products in numerous soils, climates, varieties and marketplaces.
“Lono generally averages around five percent more yield over the control, but some varieties respond particularly well. For example, there’s a chipping variety common in the United States, FL1867, where we’ve seen a 28 percent boost when LimiN technology was incorporated into the standard nutrition programme.”
Of course, the increase in marketable yield is a clear benefit, as is the avoidance – admittedly more difficult to quantify – of losses associated with the field applications of nitrogen, such as leached nitrates and ammonia and nitrous oxide emissions.
Size matters
Further field trials with SAN also revealed another interesting property.
“By revising the fertilizer schedule while using SAN, we’ve shown that farmers can accurately manipulate tuber size distribution in the field, to meet the requirements of their end market: salad potatoes, chipping, crisping and so on.
“We discovered that early pre-tuberisation SAN applications increased the percentage of smaller 40-60mm tubers. Conversely, excluding that early application and concentrating on a bulking-stage timing increased the proportion of large tubers at the 60-80mm size.”
Trials carried out in New Zealand in 2020 ably demonstrate this. Lono was applied to a crop being grown for seed potatoes – an extremely high-value end-use, where correctly sized tubers can be up to three times as valuable as those outside the optimum specification.
The trials with Lono delivered a per-hectare benefit of more than NZD4,000. “That’s quite an extreme example, because of the relatively high value of seed potatoes,” notes Dr Marks, “and a terrific demonstration of the manipulative effect of SAN.
“It’s easy to see why it’s becoming a routine treatment, especially in Europe, because of that dual effect of increased yield and consistent tuber size.
“But it’s also a great vindication of Levity’s approach to problem-solving,” sums up David. “We all need to offer growers more responsible options for nutrition and crop protection, whether it’s nitrogen in this case, or the other smart technologies we’ve pioneered, such as those for crucial trace elements like boron and molybdenum.
“Consumers increasingly expect their food to leave a smaller footprint. Delivering that challenge begins with us in the supply industry; farmers can’t do it otherwise,” he concludes.
