Sulphur fertilization is essential for green, species-rich pasture. Ultimately, this forms the basis for healthy animals and contributes to optimum milk production. Does the grass next door seem greener? With the fertilization tips from this article, that will be a thing of the past!
Many dairy farmers currently recognize the importance of sulphur fertilization for first and second cut forage grasses. Grass takes up between 75 and 125 kg of sulphur (SO3) per hectare. Until about 1990, the high rate of sulphur deposition meant there was sufficient sulphur in the soil. Today, however, annual sulphur deposition has fallen to such an extent that fertilization with extra sulphur is required to prevent sulphur deficiency in grass.
Why sulphur deficiency is a problem
Sulphur is an essential element in the formation of various amino acids, including those that are the building blocks of proteins. Sulphur deficiency can lead to a lower dry matter yield of two tonnes/ha and lower feed quality. A sulphur deficiency in the ration results in reduced milk production and a lower milk protein content combined with higher urea levels. Sulphur deficiency also leads to poorer hair and hoof quality, and slower growth in young animals.
First and second cuts
Sulphur deficits mainly occur in the springtime. Grass can only take up sulphur in mineral form, and after the winter the mineral sulphur stock in the soil is very low. This is because low soil temperature retards mineralization of the organic substance in the soil. In all soils, even peat soils, after the winter too little sulphur has been mineralized before the first cut to meet the needs of the grass. Sandy soils often require mineral sulphur fertilization not only for the first cut but also for the second.
Many dairy farmers often apply both slurry and a fertilizer with nitrogen and sulphur before the first cut. The sulphur from the slurry must first be mineralized, however, and is therefore too late for the first cut. If application must be postponed due to wet conditions, the sulphur from the applied fertilizer often also becomes available too late. Earlier top dressing, at the beginning of February for example, is not recommended, because nitrogen and sulphur easily wash out. Fortunately, since the introduction of the sulphur fertilizer Polysulphate, early top dressing is now possible.
Prolonged release of sulphur
This is because the sulphur from Polysulphate is released very gradually. Polysulphate, applied in February, provides an optimum level of sulphur for both the first and second cuts. Trials have shown that higher dry matter, VEM and DVE yields were achieved with Polysulphate. Higher sugar levels were also often found, which increases grass palatability. Therefore, our recommendation is to apply Polysulphate in February and KAS, for example, in March.
Grass and clover mixed pasture
Many organic and conventional dairy farmers grow grass/clover pastures. Sulphur and calcium are essential elements for the formation of root nodules for nitrogen fixation. Sulphur and calcium deficiencies leads to fewer root nodules and thus less nitrogen fixation, which has a negative impact on the nitrogen supply available to the grass/clover pasture. Application of Polysulphate provides sufficient plant-available sulphur and calcium for formation of the root nodules. The recommended dose of Polysulphate is 100–200 kg/ha.
–also permitted for organic farming–
ICL has marketed the natural mineral polyhalite under the name Polysulphate since 2014. This mineral contains sulphur as well as potassium, calcium, and magnesium.
Polyhalite is found in various locations around the world. However, the polyhalite layer in the North Sea bed off the English coast is the only deposit of sufficient size and purity for commercial extraction. After extraction, the unprocessed mineral is crushed and screened to a fraction of 2–4 mm. This fraction finds its way to farmers and livestock keepers worldwide. Because no chemicals are required for the extraction and processing of Polysulphate, its use is permitted for organic farming. Tip: Take part in the online workshop ‘Sulphur supply for organic dairy farms’ during the BioKennisWeek at 13:00 on Tuesday 19 January 2021.
Composition of Polysulphate
% dissolved sulphur
Prolonged nutrient release rate
Days after application