If we’re to maximize yields, against threats to food security and market uncertainty, growers must use every trick in the book to secure crops’ peak performance, says consultant agronomist Dean Konieczka of crop nutrition specialists OMEX® Agrifluids USA.
There was a time when we could afford not to worry about sulfur.
Arguably as vital a crop input as manganese, boron or zinc, sulfur is implicated in several crucial metabolic functions. The diverse processes range from nitrogen uptake to chlorophyll production, amino acid formation to vitamin synthesis, while boosting stress and pest resistance and contributing to perhaps the most important plant function of all: carbohydrate generation.
In fact, so important is sulfur that in many circles it’s elevated beyond “trace element” status: not for nothing it is commonly referred to as the “fourth macronutrient” — placing it on a par with the nutritional trinity of nitrogen, phosphorus, and potassium — because it’s instrumental in plant functions that affect yield, quality and marketability.
But why only in recent years has it come to the attention of growers and agronomists? The cynical might suggest that manufacturers and distributors are looking for new narratives to support the sale of additional crop inputs; after all, we’ve grown crops for years without applying sulfur. Yet the truth is nothing to do with opportunism and everything to do with how coal made the fourth macronutrient the invisible macronutrient.
Cleaner air, leaner crops?
Twenty-five years ago, more than half of America’s electricity was supplied by coal-fired power stations. Today, it’s less than a fifth, and 16 of the 50 states have no, or less than 10 percent, of their power production sourced from coal.
The connection? Burning coal produces sulfurous emissions. For years, these power-plant fumes carried so much sulfur that our crops never displayed deficiencies. Much like another vital input in crop production — sunlight — we never thought to supplement it because there was always enough.
But in a classic case of unintended consequences, now that we’ve recognized the effects of fossil fuels — particulates, carbon dioxide, heavy metals and the acid rain that sulfur emissions precipitated — farmers no longer receive the sulfur ‘bounty’ that had rendered top-up applications unnecessary. EPS statistics confirm that sulfur emissions dropped by 94 percent between 1990 and 2019.
As cropping has continued while background sulfur levels fall, many fields run a deficit: crops are genuinely ‘sulfur hungry’. Yet across all crops — including potatoes — sulfur deficiencies rarely produce visible symptoms. Wheat’s a great example: the gluten that’s important for breadmaking relies on sulfur-sulfur bonds. For our daily bread, wheat needs good sulfur — but its absence will only become apparent, too late, once that loaf’s been baked.
Advice for potato growers?
First, let’s look at how crops absorb sulfur. As with most elemental nutrients, plants can’t use a pure form; it must be in a compound. For sulfur, that means sulfate. And there’s a limited role for leaves: they can use small amounts of sulfur dioxide from the atmosphere (although, again, cleaner air means concentrations are lower).
Applied as a foliar spray, sulfur enters the plant tissue as needed. But this is where sulfur displays another interesting property: fungal pathogens have a natural aversion to sulfur, which is why sulfur-based products were some of the first “fungicides” available to farmers.
If growers can ensure a healthy presence of sulfur on the leaves of their potato crop, sulfur’s natural role as a disease suppressant will act in synergy with later, conventional fungicide programs. Crucially, this means the plant can stave off infections itself — which immediately reduces the selection pressure on modern fungicides, reducing the risk of fungicide resistance.
Research shows that the incidence of fungal diseases such as blight shows a close correlation with sulfur availability: the pathogen exploits even moderate deficiency. A program of foliar sulfur can also reduce scab: trials have shown a reduction of 12.5 percentage points over the control. Yet during the season, a crop’s sulfur requirements usually exceed the soil’s capacity.
Several sulfur products are suitable for use in potato crops, but each product’s effectiveness — and ultimately its return on investment — is dictated by its formulation. At OMEX®, our focus is on products that are immediately bioavailable, either because they’re unaffected by soil microbial activity or because they take advantage of specific plant characteristics.
OMEX® Cell Power® SulpHomex™ Ultra is our recommendation for potatoes. Although it contains multiple sulfur sources, it’s registered not as a fungicide, but as a fertilizer — reflecting the importance of sulfur we’ve described. Its sulphate/nitrate co-formulation allows immediate plant use in the form most readily absorbed by plant roots.
As for sulfur “philosophy”? Little and often. You’ll not only reduce leaching — environmentally unsound and an immediate loss to your bottom line — but also maintain sufficient levels of sulfur in the soil and on the leaf, making it always available to the potato crop during rapid growth. As such, lack of sulfur should never become a limiting factor in pursuing an optimized yield potential!
Consult your agronomist for the rate of OMEX® Cell Power® SulpHomex™ Ultra that’s right for your crop. Between 1 and 3-1/2 pints per acre, integrated into early-season insecticide and fungicide sprays, will not only build crops’ sulfur content, but also provide an additional mode of suppressive action that builds foundations for a healthy, high-yielding and disease-free crop.
This season, don’t just think NPK — think NPKS. Learn more at www.omexusa.com.
More from OMEX®