Fertiliser and Plant Nutrition: Prices and Practice

Reading a fertilizer label: what 29-0-10 means

The three numbers on a fertilizer bag are its grade, the percentage by weight of nitrogen (N), phosphate (P₂O₅) and potash (K₂O), always in that order. A 29-0-10 fertilizer is 29% nitrogen, no phosphate and 10% potash. A 50-pound bag therefore holds 14.5 pounds of nitrogen and 5 pounds of K₂O. The rest is the other part of each compound, plus any filler or coating. Blends like this are common for lawns and for fields where soil tests show enough phosphorus. Our article on 30-0-10 and 29-0-10 fertilizers compares them with similar grades.

One detail trips people up: phosphorus and potassium are labeled as oxides, not as the elements. To convert, multiply P₂O₅ by 0.44 to get elemental phosphorus and K₂O by 0.83 to get elemental potassium. That matters when you compare a fertilizer price with a lab price for phosphorus per gram, which is usually for a pure chemical, a different product altogether.

Main types of fertilizer for farms

Organic sources release nutrients more slowly and vary from batch to batch, so a manure analysis is worth getting before you count it in the plan. Our guide to the 17 essential plant nutrients covers the secondary nutrients and micronutrients as well.

Comparing fertilizer prices: cost per unit of nutrient

Price per ton or per bag says little on its own, because products carry very different amounts of nutrient. The fair comparison is price per pound (or kilogram) of the nutrient you need:

• Price per pound of N from urea = price per short ton ÷ (2,000 × 0.46), which is price per ton ÷ 920.
• For a metric tonne and price per kilogram, divide by 1,000 × the nutrient fraction, for example 460 for urea.
• For a mixed grade such as 10-20-20, work out the value of each nutrient at straight-product prices and compare the total with the blend’s price.

That last check shows whether a premium for a blend is worth paying. Sometimes it is, because of convenience or a crop’s need for a particular ratio. Our pages on 10-20-20 fertilizer prices and urea prices per ton have dated price examples.

Working out fertilizer cost per acre

Fertilizer cost per acre is the rate of each nutrient multiplied by its price per pound, summed across nutrients, plus application cost. The rate is the part you can control. It should come from a soil test, the crop’s removal at your expected yield and the nutrients already supplied by manure or the previous crop, such as nitrogen credits after soybeans. Agronomists summarize good practice as the 4Rs, meaning the right source, rate, timing and placement.

Rates also vary inside a field. Our satellite crop monitoring gives a fertilizer dose in kilograms for five nutrients for each field, including “apply nothing” when the crop doesn’t need any. On one 190-acre farm in Algeria, the reports showed that 3 of its 4 fields needed no fertilizer.

Timing, placement and nutrient losses

A pound of nutrient that never reaches the crop is the most expensive pound you buy. Nitrogen is lost in three main ways. Urea left on the soil surface can lose ammonia to the air, especially on warm, moist, high-pH soils, so it’s usually worked in, watered in or treated with a urease inhibitor. Nitrate washes below the root zone on sandy soils after heavy rain, which is why split applications help there. On waterlogged soils, bacteria turn nitrate into gas. Phosphorus moves little in soil but binds to it, so banding it near the seed often works better than broadcasting. Matching timing to the crop’s uptake curve does more for cost per bushel than shaving a few dollars off the price per ton.

What moves fertilizer prices

Nitrogen fertilizers are made from ammonia, and most ammonia is made from natural gas, so nitrogen prices follow gas prices closely. Phosphate depends on phosphate rock and sulfur for the acid used to process it. Potash is mined in only a few countries, with Canada, Russia and Belarus the largest suppliers, so sanctions and transport problems can move its price quickly. On top of that come freight, export restrictions and the planting season, when demand peaks.

For dated NPK fertilizer price trends, the World Bank’s monthly commodity price data includes urea, DAP, triple superphosphate and potassium chloride going back decades, and USDA market reports track US retail prices. Our summary of fertilizer prices per ton and the DTN index pulls recent figures together.