Two year survey highlights extent of sulphur deficiency
The results of a two year survey carried out by Hutchinsons and Cobb Agri has shown that sulphur levels are low in many soils, and appear to be decreasing year on year.
The survey which began in 2014 across farms in Herefordshire and Shropshire, showed that only 13% of all crops sampled had a result in the normal range, all the others were low or slightly low. The 2015 samples collected showed that 55% of crops had low sulphur levels triggering a high nitrogen: sulphur(N:S) ratio content of 16:1 or above.
“The correct N:S ratio in the plant is critical to efficient nitrogen use; a nitrogen to sulphur ratio of 12:1- 15:1 is the normal range, and indicates adequate sulphur levels. However if this goes up to 16:1 –or 17:1, this indicates lower levels of sulphur, whilst a reading of 18: 1 would mean a low sulphur status and the need for a sulphur treatment for the next crop,” says Andrew Goodinson of Hutchinsons.
“We felt that it was important to monitor levels on an annual basis as results can vary season to season, depending on factors such as rainfall how much sulphur has been applied and the amount of nitrogen taken up by the crop. By testing the grain we are able to say that the results are reliable as possible, as this is the most accurate way to access sulphur levels in the soil, as we have found tissue analysis not be as reliable.”
He notes that these results underline the extent to which soils are becoming depleted of sulphur, with detrimental effects on overall crop health. Sulphur is a major fundamental nutrient needed for plant establishment, development and even crop maturity. It also helps to increase yield and protein within wheat.
“I always refer to the analogy of nitrogen being the building blocks for protein and growth, whilst sulphur is the mortar.”
Continuous intensive arable crops with high-yield crop varieties have depleted sulphur in the ground and at the same time atmospheric deposition is not occurring to maintain the sulphur levels, causing a sulphur deficiency.
The lower levels in 2015 are most likely a result of the high yielding crops in the 2015 harvest which used up much of the nitrogen in the soil, upsetting the nitrogen to sulphur ratio.
“Given the close relationship between nitrogen and sulphur in plant nutrition, it’s crucial to address these low levels and to prevent underutilisation of any further nitrogen applications,” he says.
Addressing low sulphur levels
The good news is that it is a reasonably easy problem to rectify and not too costly, says Tim Kerr, national fertiliser manager for Hutchinsons.
“Start thinking about it now so you have time to address any low levels for this season. Annual applications of sulphur will be necessary to meet future crop demands and to utilise nitrogen to its full capacity, this is because sulphate levels are easily reduced from the soil through plant uptake and leaching as sulphur is water soluble.”
“Sulphur must be applied to the soil at the right growth stage, we recommend applying it at the first and second pass of nitrogen. We would generally recommend the addition of 75kgs/ha of sulphur to winter wheat, and a 100kgs/ha of sulphur to oilseed rape.”
“Results have shown that where farm yard manure is being used, sulphur levels are generally better.”
We cannot afford to compromise crop development in any way this seasons, he adds, and when growers are taking a very measured approached to how they are using their inputs, this is an important message.
