Plants can absorb three different types of nitrogen: nitrate, ammonium and amine. They exhibit different responses to these three forms, and expend varying amounts of energy in using them
Every grower’s playbook will also emphasize the importance of nitrogen to the growing potato crop, recognizing the varying regimes required by stock heading for different markets, and underlining how optimum yield and quality are affected by timing of nitrogen applications.
But what a lot of playbooks don’t mention is how the crop in your field is making use of only 25 to 35 percent of the nitrogen fertilizer you’re applying.
“Just let that sink in for a moment,” says Francisco. “Every time you apply nitrogen to the crop, it’s unable to access as much as three-quarters of it, thanks to leaching, microbial action and mineralization before the plant’s able to absorb it.
“That’s because the most used forms of nitrogen are those recommended by chemists, rather than biologists,” he explains, “and are based on what’s been easiest to source in large quantities.”
Every plant demands nitrogen. It’s an essential component of chlorophyll, the light-capturing photosynthetic compound that helps plants transform sunlight into carbohydrates. Proteins and their building blocks, amino acids, are built around nitrogen too.
“Many growers might be aware by now that different types of nitrogen appear to behave differently in the field,” points out Francisco, “and the science is bearing this out, raising exciting possibilities to influence crop growth and final yield, while improving efficiency of nitrogen applications.
“Plants can absorb three different types of nitrogen,” notes Francisco, “nitrate, ammonium and amine. They exhibit different responses to these three forms, and expend varying amounts of energy in using them.”
For example, nitrates will stimulate leafy growth and ‘apical dominance’, with leggy crops and poor lateral root production the result. But while ammonium will produce a plant with the same biomass for a given amount of nitrogen, more of it will be found in the roots and tubers.
However, most soil-applied nitrogen is quickly converted from ammonium to nitrate by soil microbes; when the plant absorbs it, it must convert it back to ammonium. Conversion is an energy-intensive process.
“We talk about plant energy usage in terms of ‘carbon’,” says Francisco. “Carbon compounds are how the plant captures solar energy for its own use. When the plant turns its absorbed nitrate back into ammonium, it takes 12 times more carbon to turn that nitrate into plant protein than for the same unit of nitrogen absorbed as an amine.
“Whereas amine or ammonium can be used immediately in protein synthesis, and the plant can instead put its captured photosynthetic energy into growth.”
All very well in theory, but there’s a problem. Ammonium applied to the soil doesn’t stay ammonium for very long; soil bacteria turn it into carbon dioxide and ammonia, both of which are lost to the atmosphere, and nitrate – with all its energy-use disadvantages.
OMEX® has been working for several years with a British agri-tech firm, Levity Crop Science, that has successfully ‘rethought’ this nitrogen dilemma. Coming at the problem from a biological point of view, it’s applied its understanding of plant physiology and nitrogen uptake to formulate and produce a fertilizer technology that can dramatically improve nitrogen fertilizer use efficiency (NFUE), using a stabilized form of amine urea.
The concept of stabilizing urea isn’t new; polymer coatings that inhibit urea decomposition have featured in crop production for some time. But Levity has eschewed physical barriers for a more comprehensive – and more effective – chemical approach. While the chemistry’s complicated, the result is far from: the amine effectively becomes invisible to the soil bacteria that usually target it. Levity’s technology, LimiN, now features within OMEX®’s Cell Power® SizeN® formulations.
“By applying SizeN®, the crop has more nitrogen, in a more energy-efficient form,” says Francisco. “We don’t have to apply as much for the same response in plant growth. And because the nitrogen’s in amine form, we get a better response below ground too, in tuber numbers, size and uniformity.”
Trials around the world, on many different varieties, have demonstrated how SAN-treated potato crops deliver much greater marketable yields, averaging around five per cent over the control. Further trials have also shown how revising the fertilizer schedule while using SAN can help manipulate tuber size distribution in the field, improving mean marketable yield by around 44-53 cwt/acre.
“European growers, especially those in Ireland, Netherlands and the U.K., have been using SAN-based products for a few years now,” reports Francisco, “and many are already seeing it as a routine treatment, thanks to its combined offering of improving yields and a more consistent tuber size.
“As we focus more on efficiencies within agriculture, particularly where environmental aspects are concerned, products like SizeN® also provide growers with a more responsible approach to nitrogen management. Processors and buyers are also becoming more aware that consumers are expecting their food to leave a smaller footprint.”
Learn more about potatoes absorb N
