Soil & Fertilizer calculators

Start from the crop's recommended NPK dose (kg/ha of N, P₂O₅ and K₂O). Supply phosphorus first with DAP (which also adds some N), then top up the remaining nitrogen with urea (46% N), and supply potash with MOP (60% K₂O). The Fertilizer (NPK) Calculator does this back-calculation and converts to bags and cost. Example: a 120-60-40 dose ≈ 130 kg DAP + 215 kg urea + 67 kg MOP per hectare.

Lime need depends on how far below target the pH is, the soil's buffering (texture/CEC) and the lime's neutralising value. A light sandy soil may need 1–2 t/ha to move one pH unit; a heavy clay can need 4–6 t/ha. A buffer-pH test gives the most accurate rate. Use the Lime Requirement or Buffer pH Lime calculator.

Aim for a starting carbon-to-nitrogen ratio of about 25–35:1 by weight. Too much carbon (>40:1) composts slowly and can tie up soil nitrogen; too much nitrogen (<20:1) goes anaerobic and smells of ammonia. Finished, mature compost settles near 10–15:1. The Compost C:N and Compost Recipe calculators balance your greens and browns.

Saline soils have high soluble salts (ECe > 4 dS/m) but normal sodium; sodic soils have ESP > 15 (or SAR > 13) and poor structure even at low EC; saline-sodic soils have both. Saline soils are reclaimed by leaching, sodic soils by adding gypsum or sulphur first, then leaching. The Salt-Affected Soil Classification tool plots ECe × ESP/SAR and names the route.

Always compare cost per kg of nutrient, not per bag. A cheaper-looking bag can carry less N, P or K. Cost per kg N = bag price ÷ (bag weight × N fraction). The Fertilizer Cost per Nutrient calculator ranks products by the real price of each kg of N, P₂O₅ and K₂O.

Walk a zig-zag over a uniform area (ideally ≤ 1–2 ha per sample), take 10–20 cores to plough depth (0–15 cm), mix them in a clean bucket and submit about 500 g as one composite sample. Sample separate zones (different soil, slope or crop history) on their own. The Soil Sampling Plan calculator sizes cores and samples for your field.

Partly. Farmyard manure at ~0.5-0.2-0.5% N-P-K supplies roughly 5 kg N, 2 kg P₂O₅ and 5 kg K₂O per tonne, but only a fraction mineralises in year one. A 10 t/ha FYM dose might credit ~25–30 kg available N the first season, releasing more over years 2–3. Use the FYM Fertilizer Equivalent and Manure Mineralization calculators to credit it accurately.

Surface-applied urea hydrolyses to ammonia, which volatilises — losses of 10–40% are common on warm, moist, high-pH or residue-covered soils left unincorporated. Incorporating, irrigating in, deep placement, or using neem-coated urea / a urease inhibitor cuts this sharply. The Urea Volatilization Loss calculator estimates your loss.

Cation Exchange Capacity (CEC, in cmol(+)/kg or meq/100 g) is the soil's capacity to hold positively-charged nutrients — Ca, Mg, K, NH₄. Sandy soils sit near 3–8, clays and high-organic soils reach 20–40+. Low-CEC soils hold little nutrient and leach easily, so split applications pay. The CEC & Base Saturation tool reads it from your soil test.

Foliar sprays correct an in-season deficiency fast and use far less product (e.g. 0.5% zinc sulphate), but each spray delivers little and washes off. Soil application lasts longer for chronic deficiency. For high-pH soils where iron or zinc gets locked up, a chelate or foliar route often wins. The Foliar vs Soil Application tool compares cost per delivered kg.

Keep the injected solution dilute in-line (broadly under ~1–2 g/L of soluble fertilizer), inject after the system fills and flush with clean water before shutdown. Calculate the per-event dose, the stock-tank strength and the injection time so you never exceed safe concentration. The Fertigation, Stock Tank and Injection Time calculators handle each step.

The profit-maximising nitrogen rate (MRTN) is lower than the yield-maximising rate — it's where the last kg of N just pays for itself at today's N and grain prices. As N gets dearer relative to grain, the economic rate drops. The Economic N-Rate (MRTN) 4R calculator finds it and shows the profitable-rate band.