Sri Lanka Paddy Fertilizer Calculator — Urea, TSP & MOP per acre

The Department of Agriculture, through the Rice Research and Development Institute (RRDI), publishes rice fertilizer recommendations as fixed per-hectare quantities for four cases: your agro-ecological zone (Wet Zone, or Intermediate & Dry Zone) combined with your water regime (irrigated or rainfed). Each case gives a total of Urea, Triple Super Phosphate (TSP), Muriate of Potash (MOP) and zinc sulphate, plus how to split those totals across the season. This calculator applies those tables directly — it is a deterministic lookup and linear scaling, not a model or estimate.

1. Select the recommendation row. Your zone × water regime picks one of the four DOA tables. Your rice age class (3, 3½ or 4 months) sets the timing of the later top dressings.
2. Convert extent to hectares. Recommendations are per hectare, so the tool converts your area: hectares stay as-is, acres are divided by 2.47105, and perches are divided by 160 then by 2.47105 (160 perches = 1 acre).
3. Scale each nutrient. For every fertilizer,total kg = rate per hectare × hectares. Fertilizer recommendations scale linearly with area.
4. Scale each stage. The same scaling is applied to every stage of the schedule, so the basal and each top-dressing row show the kilograms to apply across your whole plot — not per hectare.
5. Round to bags. Each fertilizer is rounded up to whole 50 kg bags (the standard sale unit), with the loose kilograms in the final bag shown for context.

Two rules hold across every DOA rice table and are worth knowing: all TSP and all zinc sulphate go in at basal (they are soil-stable nutrients), and no Urea is applied at basal — nitrogen is held back and split across the top dressings so it is not lost to the standing water. As a credibility check, the per-stage amounts on this page are summed and compared with the DOA per-hectare totals; they reconcile to the kilogram for every zone and age class.

Cost is optional and never assumed. Fertilizer prices move with market and subsidy conditions and have no stable published feed, so you enter your own shop price per 50 kg bag; the tool then computes cost = (total kg ÷ 50) × price per bag for Urea, TSP and MOP and totals them.

• DOA / RRDI — Rice Fertilizer Recommendation index
• DOA / RRDI — Intermediate & Dry Zone, irrigated
• DOA / RRDI — Intermediate & Dry Zone, rainfed
• DOA / RRDI — Wet Zone, irrigated
• DOA / RRDI — Wet Zone, rainfed
• DOA — Fertilizer Recommendation portal (methodology)

Quantities were transcribed from the DOA/RRDI pages above and each zone's split stages were reconciled against its published per-hectare totals on 2026-07-05. Rice recommendations are research-based and stable across seasons; this page is reviewed whenever the DOA revises the recommendation.