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Sulphur deserves more attention that it gets. It is important for plants, cheap and can easily be incorporated into fertiliser applications.
Sulphur (S) is vital in any farm setting, but often lacking in New Zealand soils, especially in spring when most needed. Despite being relatively cheap and straightforward to apply with other nutrients, S can be easily overlooked.
Vital for plants and production
To grow, plants need S. Required for clover and pasture growth, it is part of many enzymes important for biochemical processes, some proteins and vitamins, and is vital for chlorophyll production. Clover in particular needs S; the Rhizobia bacteria in the root nodules require it for nitrogen (N) fixation. If plant growth suffers due to S deficiency, pastures appear pale green or yellow, with clover affected first. Insufficient S can also limit pasture response to N, particularly if S levels are low after a wet winter.
In fertiliser, S is either:
• sulphate S, the only form which plants can use, and which leaches readily
• elemental sulphur, which plants cannot use (until soil bacteria convert it into sulphate-S), and which does not leach
Applying early spring S
On ryegrass dominant pastures in early spring, if an immediate S deficiency (where sulphate levels are in single figures) is likely to limit pasture response to N, then sulphate-S may need to be added with N, as elemental and organic S release of S will be too slow. Consider products such as sulphate of ammonia (SOA), SustaiN Ammo (containing sulphate-S) or PhasedN Quick Start (containing sulphate and elemental S) to ensure early spring pasture.
Spring’s S shortage
Sulphate-S in soil is often in short supply in early spring. Winter is a double blow for sulphate-S.
Bacteria are less active and slower at converting organic and elemental S into sulphate-S, and sulphate-S leaches over wet winter conditions. Soil type and rainfall impact the degree of S leaching over winter; coarse soils such as sands and pumice suffer greater leaching than ash or sedimentary soils.
Elemental S, on the other hand, does not leach. As soil temperatures warm up in spring, bacteria become more active and gradually convert elemental S into sulphate-S.
Adequate levels of sulphate-S are needed for spring pasture to thrive. When sulphate-S is deficient, if N fertiliser is applied the response to N can be limited and spring clover growth patchy or poor.
To choose the right S product, consider timing of plant requirements and application, the leaching risk (taking into account the soil type and rainfall) and if it will be applied with other nutrients.
Annual maintenance S
As a general rule, sulphate-S can be applied in spring and elemental S in autumn. The exception is high rainfall areas (>1500 mm) where a mix of sulphate and elemental S should be applied in spring.
If superphosphate-based fertiliser (typically .SuperPlus or SurePhos) is applied annually to soils with low risk of leaching (<1500 mm) in spring, there is normally no need for additional S applications. If it is not applied, or if an alternative phosphate fertiliser without S is used, a separate application of S is needed, either in elemental or sulphate form.
If applying S or maintenance fertiliser in autumn, use a product containing some elemental S, as it sits in the soil over winter ready to meet spring pasture’s S requirements, and provides a slow release of S over the growing season.
For autumn application, products such as the Sulphurgain range (15S, 20S, 30S) are an effective way of applying elemental S along with maintenance phosphorus requirements. Where phosphate fertilisers are used that do not contain S, products such as Sulphurgain Pure containing 90 per cent S as elemental S, or PhaSedN containing elemental S and N (as SustaiN) are good options.