20-20-0-13 (Ammonium Phosphate Sulphate)

20-20-0-13, also known as ammonium phosphate sulphate (APS), is one of the most widely used Indian complex fertilisers. The grade supplies 20% nitrogen, 20% P2O5 and 13% sulphur in a single granule, with no potash. It occupies the slot between Dap and the 10-26-26 NPK grade in basal-fertiliser choice for paddy, oilseeds, pulses, onion, garlic, chilli, sugarcane and cotton on sulphur-deficient soils.

Composition

Grade: 20-20-0-13 (N-P2O5-K2O-S)
N forms: 18% ammoniacal + 2% amide
P solubility: approximately 85% of total P in water-soluble form
S form: sulphate, plant-available
Manufacturers: IFFCO (NP 20:20), GSFC, Coromandel (Gromor 20-20-0-13), Sakthi (Sardar 20:20:0:13)

Mode of action

The ammoniacal nitrogen is taken up directly or nitrified to nitrate, while the small amide fraction provides delayed release. The water-soluble phosphate is released into the immediate root zone, and the sulphate fraction supplies sulphur for amino-acid and oil synthesis in oilseeds, brassicas and alliums.

Target use and dose

APS is applied as a basal at sowing or transplanting at rates set by crop and soil test, typically 50-100 kg per acre for field crops. It is used as an alternative basal to Dap where soils are sulphur deficient and a separate sulphur application would otherwise be needed. In cotton it is used as an alternative basal to 14-35-14 (see Complex Npk Grades) and gives stronger branching than DAP at the cost of slightly lower phosphate concentration.

Subsidy and regulation

Notified under the FCO complex-fertiliser schedule, with retail price regulated under the Nutrient-Based Subsidy regime; per-nutrient subsidy is announced twice a year.

References

Ammonium Phosphate Sulphate 20:20:0:13. Gujarat State Fertilizers & Chemicals Limited.
NP-20:20 Ammonium Phosphate Sulphate. Indian Farmers Fertiliser Cooperative.