NPK Fertilizer Blend from Soil Test
Nutrient recommendation (max(0, crop demand - soil-test credit)) for N / P2O5 / K2O.
Example
You enter
- Crop corn
- Soil-test N credit (lb/acre) 20
- Soil-test P2O5 credit (lb/acre) 10
- Soil-test K2O credit (lb/acre) 15
- Field area (acres) 80
You get
- Nutrient recommendation 130
- Rec p lb per acre 50
- Rec k lb per acre 25
- Urea lb per acre 240.08
- Dap lb per acre 108.7
- Mop lb per acre 41.67
Checked against published worked examples from: USDA NRCS.
Details, formula, and sources
ScopeSolved into a three-straight blend (urea, DAP, potash) with delivered nutrients and over-application flags. Per USDA NRCS Agronomy Technical Note ranges; certified soil-test recommendation governs.
Formula or tableNutrient recommendation = max(0, crop demand - soil-test credit) for each of N, P2O5, K2O. Three-straight blend: potash (lb/acre) = K2O rec / 0.60; DAP = P2O5 rec / 0.46 (carrying N = DAP x 0.18); urea = max(0, N rec - N from DAP) / 0.46. Total product = rate x acres.
Source and editionUSDA NRCS Agronomy Technical Note ranges and the state Cooperative Extension Service published recommendations (state-keyed) by name.
Free accessFree at nrcs.usda.gov.
What governsEstimate. AHJ and licensed professional govern.
API field namescrop, soil_n_lb_per_acre, soil_p_lb_per_acre, soil_k_lb_per_acre, area_acres, rec_n_lb_per_acre, rec_p_lb_per_acre, rec_k_lb_per_acre, urea_lb_per_acre, dap_lb_per_acre, mop_lb_per_acre
- Default fertilizer grades urea 46-0-0, DAP 18-46-0, potash 0-0-60common straight fertilizers
- Representative crop demand corn 150-60-40, wheat 100-50-30, soybeans 0-45-80 lb/acre N-P2O5-K2ONRCS Agronomy Technical Note ranges
- Soil-test credit subtracted from crop demand, floored at zeroExtension nutrient-budget method