Agronomic Services

Crop Fertilization Based on North Carolina Soil Tests

Table 1.4  Multiplication factors for converting soil test index values to a quantitative equivalent*
Soil Test Index Value	mg/dm³	kg/ha	lb/acre	meq/100 cm³	meq/dm³
P-I	1.2	2.40	2.138	N/A	N/A
K-I	1.955	3.91	3.484	0.005	0.05
Ca% × CEC	200.0	400.0	356.40	1.0	10.0
Mg% × CEC	121.6	243.2	216.69	1.0	10.0
Na	230.0	460.0	409.86	1.0	10.0
Mn-I	0.16	0.32	0.285	N/A	N/A
Zn-I	0.04	0.08	0.071	N/A	N/A
Cu-I	0.02	0.04	0.036	N/A	N/A
S-I	0.48	0.96	0.857	N/A	N/A
* Soil tests in North Carolina are made on a volume of soil. Conversion to an area equivalent is based on a depth of 20 cm (7.9 inches). To convert phosphorus and potassium from the elemental forms to lb/acre, use these multipliers: 2.29 × P gives lb of P2O5 per acre; and 1.2 × K gives lb of K2O per acre. The Volume Rationale: The area of a hectare (ha) is 10,000 m² or 1,000,000 dm². The volume per hectare to a depth of 20 cm or 2 dm equals 2,000,000 dm³. The following conversion factors apply: mg/dm³ = parts per million (ppm); mg/dm³ × 2 = kg/ha; kg/ha × 0.893 = lb/acre; or mg/dm³ × 1.78 = lb/acre. Refer to Part IV of this manual for other conversion factors.
Hardy DH, Tucker MR, Stokes CE. 2013. Crop fertilization based on North Carolina soil tests. Raleigh (NC): North Carolina Department of Agriculture and Consumer Services, Agronomic Division. Circular No. 1.