Ammonium sulfate is the only common fertilizer that delivers both nitrogen and sulphur in a single product. In East Africa, where sulphur deficiency affects over 60 % of cropland, this dual benefit makes ammonium sulfate a smart choice — if you apply it correctly for your specific crop.
Sulphur is the fourth most important nutrient after N, P, and K. It is essential for protein synthesis, oil formation, and chlorophyll production. Sulphur-deficient crops produce lower yields and poorer quality grain — wheat has lower protein content, coffee has reduced flavour complexity, and maize has weaker stalks.
Kenya's sulphur deficiency has worsened as farmers switched from single superphosphate (which contained 12 % S) to DAP (which contains no sulphur). Ammonium sulfate fills this gap.
For maize, ammonium sulfate works best as a partial replacement for urea at the first top-dressing. A practical blend: 70 kg/ha of urea + 100 kg/ha of ammonium sulfate. This delivers approximately 53 kg N per hectare plus 24 kg S — addressing both nitrogen and sulphur needs in one application.
The ammonium form of nitrogen in AS is less prone to volatilization than urea, making it a safer choice in hot, dry conditions. However, it is more acidifying — on already acidic soils (pH below 5.5), monitor pH and apply lime as needed.
Wheat quality is directly linked to grain protein content, which depends on adequate nitrogen and sulphur supply. Research in Kenya's Narok and Nakuru wheat-growing areas shows that ammonium sulfate application increases grain protein by 1-2 percentage points compared to urea alone.
Recommended rate: 150-200 kg/ha of ammonium sulfate applied in two splits — half at planting and half at tillering (4-6 weeks after emergence).
Coffee is a heavy feeder of both nitrogen and sulphur. Sulphur contributes to the development of flavour precursors in the bean. Kenyan coffee research recommends 200-300 kg/ha of ammonium sulfate per year, split into 2-3 applications aligned with the rainy seasons.
Apply around the drip line of the tree and lightly incorporate. On acidic coffee soils (common in the Central Highlands), monitor pH annually and lime as needed.
Crop | AS Rate (kg/ha) | Timing | N Delivered | S Delivered |
Maize (with urea) | 100 | Knee-height top-dress | 21 kg | 24 kg |
Wheat | 150-200 | Split: planting + tillering | 31-42 kg | 36-48 kg |
Coffee | 200-300/year | 2-3 applications per year | 42-63 kg | 48-72 kg |
Tea | 150-200/year | 3-4 applications per year | 31-42 kg | 36-48 kg |
Ammonium sulfate (21-0-0-24S) is uniquely valuable in East Africa because it addresses the widespread sulphur deficiency alongside nitrogen needs. For maize, blend with urea. For wheat, use full-rate AS for protein quality. For coffee, apply in split doses aligned with growth flushes.
Q: Is ammonium sulfate acidic? Will it harm my soil?
A: Ammonium sulfate is acidifying — it lowers soil pH over time. On neutral or alkaline soils, this is actually beneficial. On already acidic soils (pH below 5.5), monitor pH and apply lime (calcium carbonate) every 2-3 years to maintain balance.
Q: Can I use ammonium sulfate for top-dressing in dry conditions?
A: Yes, and it is actually safer than urea in dry conditions. Ammonium nitrogen is less prone to volatilization losses than urea nitrogen. However, for best results, apply before rain or irrigate after application.
Q: How does ammonium sulfate compare to urea on cost per unit of nitrogen?
A: Urea delivers 46 % N; ammonium sulfate delivers 21 % N. Per unit of nitrogen, urea is usually cheaper. However, ammonium sulfate provides 'free' sulphur — when you factor in the cost of separate sulphur application, AS can be more cost-effective on sulphur-deficient soils.
Maxing supplies ammonium sulfate (21-0-0-24S) in bulk and 50 kg bags for East African markets. Contact ops@qdmaxing.com for specifications and FOB pricing.
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