# Agronomic Services

## Crop Fertilization Based on North Carolina Soil Tests

Table 2.4Equations for calculating rates of P2O5 and K2O *Equation Reference No. Equation 1 0.0467 I² – 13.0 I + 900 = lb/acre 2 0.0202 I² – 6.37 I + 500 = lb/acre 3 0.0100 I² – 3.50 I + 300 = lb/acre 4 0.0175 I² – 4.46 I + 300 = lb/acre 5 0.0193 I² – 4.90 I + 300 = lb/acre 6 0.0272 I² – 6.08 I + 300 = lb/acre 7 0.0100 I² – 3.25 I + 250 = lb/acre 8 0.0173 I² – 4.64 I + 250 = lb/acre 9 0.0102 I² – 3.00 I + 220 = lb/acre 10 0.0103 I² – 2.90 I + 200 = lb/acre 11 0.0190 I² – 4.20 I + 200 = lb/acre 12 0.0053 I² – 2.00 I + 180 = lb/acre 13 0.0120 I² – 2.90 I + 165 = lb/acre 14 0.0116 I² – 2.75 I + 150 = lb/acre 15 0.0140 I² – 3.20 I + 150 = lb/acre 16 0.0227 I² – 4.42 I + 150 = lb/acre 17 0.0084 I² – 2.19 I + 140 = lb/acre 18 0.0120 I² – 3.00 I + 120 = lb/acre 19 0.0044 I² – 1.60 I + 100 = lb/acre 20 0.0120 I² – 2.40 I + 80 = lb/acre 21 0.0012 I² – 0.315 I + 20 = lb/1000 ft² 22 0.0005 I² – 0.418 I + 11 = lb/1000 ft² 23 0.0005 I² – 0.135 I + 9 = lb/1000 ft² 24 0.0007 I² – 0.160 I + 8 = lb/1000 ft² 25 0.0005 I² – 0.130 I + 6.5 = lb/1000 ft² *Refer to Table 2.3 to match the appropriate equation with the desired crop. Insert the current soil test index value (I) into the equation and solve for the suggested fertilizer rates. The rate of fertilizer suggested ranges 10 lb above and below the calculated value. The results of the above equations for specific soil test indexes are shown in Table 2.5.

Last Update
January 10, 2014