# Agronomic Services

##### Crop Fertilization Based on North Carolina Soil Tests

Table 2.4 Equations for calculating rates of P2O5 and K2O * |
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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. |
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Last Update
January 10, 2014