Sulphur levels on the low side following extreme wet conditions
AS most potato growers will already know, some nutrients have higher mobility levels within soils than others, meaning they are at a greater risk of leaching out of soils (or at least down the soil profile where shallow, restricted or young roots are unable to access them). Sulphur is one of the higher profile culprits, alongside nitrogen.
Last year’s wet conditions showed very visibly in fields where nitrogen inputs were delayed because of ground conditions, or in trials where nitrogen was not applied. This stands to reason, owing to the aforementioned mobility, exacerbated by the sheer volume of rainfall.
With the overriding focus on nitrogen last year, sulphur hasn’t quite had the same focus, yet the outcome for this nutrient last year was just the same. Although the scale of response may not be the same as that of nitrogen, its impact is far reaching, affecting yield, quality and the optimisation of nitrogen.
Data from both NRM and Lancrop Laboratories over the past two years have shown the increase in crops with low sulphur levels. Signs of sulphur deficiency in potato plants can include upward curving of the leaves or the plant turning a lighter green to yellow color. Deficient sulphur levels can result in poor crop growth, delayed maturity and spindly plants.
Chlorosis can also result from severe sulphur deficiency, with plants showing pale green/yellow leaves that are reduced in size and growth may be stunted. Often seen on younger leaves first.
Although most potato growers have had some respite from the rain in recent weeks, the current season has continued where the last left off for most, and it is likely that once again sulphur levels will be on the low side.
Whilst slurries, manures and digestates all contain sulphur, the quantities and form of sulphur can vary considerably, depending on feeding and storage practices. Variations of between 5 and 55% availability have been identified in availability of sulphur from cattle slurry. Conversions of plant available inorganic sulphur to organic sulphur or reduced to sulphide may be part of the reason for this variation.
With high levels of uncertainty, it is difficult to rely on this source alone to meet a crop’s sulphur requirement, unless soils have had regular applications of manures over a long period of time. Therefore, in one form or another, it is very likely that sulphur will be required this year by most crops, and this should be planned in early when making nutrient management plans this season.
Source: PDA / Potassium+ / Yara Photo: Yara
