Sunflower will respond to fertilization. Nitrogen, phosphate, and potash are important. The tables that follow list appropriate recommendations.

## Nitrogen

We base nitrogen (N) fertilizer guidelines on the results of a soil NO_{3}^{-}-N test or the consideration of expected yield, previous crop, and soil organic matter content. The soil NO_{3}^{-}-N test is appropriate for western Minnesota (see Figure 1). With the soil nitrate test, we use the following calculation:

N_{rec} = (0.05) (EY) - STN_{(0-24 in.)} - N_{Pc}

Where:

EY = expected yield (lb./acre)

STN = nitrate-nitrogen (NO_{3}^{-}-N) measured to a depth of 24 in. (lb./acre)

Npc = amount of N supplied by the previous legume crop (lb./acre).

Table 1 summarizes these N credits.

Table 2 summarizes the N fertilizer guidelines for situations where the soil NO_{3}^{-}-N test is not used.

Table 1 lists legume crops that might precede sunflower in a crop rotation. Use these credits for the N_{pc} factor when you use the soil nitrate test.

* Add 20 lbs. of N per acre to the listed credits if the third or fourth cutting wasn’t harvested.

## Table 1: Nitrogen credits

Previous crop | First-year nitrogen credit |
---|---|

Soybean | 20 lbs. of N per acre |

Edible beans, field peas | 10 lbs. of N per acre |

Harvest sweetclover | 10 lbs. of N per acre |

Harvested alfalfa*: 4 to 5 plants per square foot | 75 lbs. of N per acre |

Harvested alfalfa*: 2 to 3 plants per square foot | 50 lbs. of N per acre |

Harvested alfalfa*: 1 or fewer plants per square foot | 0 lbs. of N per acre |

Harvested red clover per square foot | 35 lbs. of N per acre |

## Table 2: Nitrogen fertilizer guidelines

Crop grown last year | Organic matter level* | Expected yield: 1,400-1,900 lbs. per acre | Expected yield: 1,901-2,400 lbs. per acre | Expected yield: 2,401-2,900 lbs. per acre | Expected yield: 2,901-3,300 lbs. per acre | Expected yield: 3,300+ lbs. per acre |
---|---|---|---|---|---|---|

Alfalfa (4+ plants per square foot) | Low | 0 lbs. of N per acre | 0 lbs. of N per acre | 0 lbs. of N per acre | 0 lbs. of N per acre | 0 lbs. of N per acre |

Alfalfa (4+ plants per square foot) | Medium and high | 0 lbs. of N per acre | 0 lbs. of N per acre | 0 lbs. of N per acre | 0 lbs. of N per acre | 0 lbs. of N per acre |

Alfalfa (2 to 3 plants per square foot) | Low | 0 lbs. of N per acre | 20 lbs. of N per acre | 40 lbs. of N per acre | 60 lbs. of N per acre | 80 lbs. of N per acre |

Alfalfa (2 to 3 plants per square foot) | Medium and high | 0 lbs. of N per acre | 0 lbs. of N per acre | 10 lbs. of N per acre | 30 lbs. of N per acre | 50 lbs. of N per acre |

Soybeans | Low | 30 lbs. of N per acre | 50 lbs. of N per acre | 70 lbs. of N per acre | 90 lbs. of N per acre | 110 lbs. of N per acre |

Alfalfa (1 or fewer plants per square foot) | Medium and high | 0 lbs. of N per acre | 20 lbs. of N per acre | 40 lbs. of N per acre | 60 lbs. of N per acre | 80 lbs. of N per acre |

Group 1 crops (see below) | Low | 0 lbs. of N per acre | 15 lbs. of N per acre | 25 lbs. of N per acre | 45 lbs. of N per acre | 65 lbs. of N per acre |

Group 1 crops (see below) | Medium and high | 0 lbs. of N per acre | 0 lbs. of N per acre | 0 lbs. of N per acre | 25 lbs. of N per acre | 45 lbs. of N per acre |

Group 2 crops (see below) | Low | 70 lbs. of N per acre | 90 lbs. of N per acre | 110 lbs. of N per acre | 130 lbs. of N per acre | 150 lbs. of N per acre |

Group 2 crops (see below) | Medium and high | 40 lbs. of N per acre | 60 lbs. of N per acre | 80 lbs. of N per acre | 100 lbs. of N per acre | 120 lbs. of N per acre |

**Low = less than 3.0%; medium and high = 3.0% or more.*

Use these recommendations for sunflower production when the soil NO3--N test isn’t used.

#### Crops in Group 1

Alsike clover, birdsfoot trefoil, grass/legume hay, grass legume pasture, fallow and red clover.

#### Crops in Group 2

Barley, buckwheat, canola, corn, grass hay, grass pasture, oat, potato, rye, sorghum-sudan, sugar beet, sunflower, sweet corn, triticale and wheat.

## Phosphate, potash and other nutrients

Table 3 summarizes phosphate recommendations for sunflower production in Minnesota. Use one of the following equations if you want a phosphate guideline for a specific soil test and a specific expected yield:

- P
_{2}O_{5}rec = [0.0225 - (0.0011) (Bray P in ppm)] (Expected yield) - P
_{2}O_{5}rec = [0.0225 - (0.0014) (Olsen P in ppm)] (Expected yield)

## Table 3: Phosphate fertilizer suggestions

Expected yield | P soil test: 0-5 parts per million (ppm) Bray and 0-3 ppm Olsen | P soil test: 6-10 ppm Bray and 4-7 ppm Olsen | P soil test: 11-15 ppm Bray and 8-11 ppm Olsen | P soil test: 16-20 ppm Bray and 12-15 ppm Olsen | P soil test: 21+ ppm Bray and 16+ ppm Olsen |
---|---|---|---|---|---|

1,400-1,900 lbs. per acre | 55 lbs. of P2O5 per acre | 35 lbs. of P2O5 per acre | 15 lbs. of P2O5 per acre | 0 lbs. of P2O5 per acre | 0 lbs. of P2O5 per acre |

1,901-2,400 lbs. per acre | 65 lbs. of P2O5 per acre | 45 lbs. of P2O5 per acre | 20 lbs. of P2O5 per acre | 0 lbs. of P2O5 per acre | 0 lbs. of P2O5 per acre |

2,401-2,900 lbs. per acre | 75 lbs. of P2O5 per acre | 55 lbs. of P2O5 per acre | 25 lbs. of P2O5 per acre | 0 lbs. of P2O5 per acre | 0 lbs. of P2O5 per acre |

2,901-3,300 lbs. per acre | 85 lbs. of P2O5 per acre | 65 lbs. of P2O5 per acre | 25 lbs. of P2O5 per acre | 10 lbs. of P2O5 per acre | 0 lbs. of P2O5 per acre |

3,300+ lbs. per acre | 90 lbs. of P2O5 per acre | 70 lbs. of P2O5 per acre | 30 lbs. of P2O5 per acre | 10 lbs. of P2O5 per acre | 0 lbs. of P2O5 per acre |

Use the following equation if you want a potash guideline for a specific soil test and a specific expected yield:

K_{2}O rec = [0.0410 - (0.00027) (Soil test K in ppm)] (Expected yield)

## Table 4: Potash fertilizer suggestions for sunflower production in Minnesota

Expected yield | K soil test: 0-40 ppm | K soil test: 41-80 ppm | K soil test: 81-120 ppm | K soil test: 121-160 ppm | K soil test: 161+ ppm |
---|---|---|---|---|---|

1,400-1,900 lbs. per acre | 55 lbs. of K2O per acre | 40 lbs. of K2O per acre | 20 lbs. of K2O per acre | 15 lbs. of K2O per acre | 0 lbs. of K2O per acre |

1,901-2,400 lbs. per acre | 75 lbs. of K2O per acre | 50 lbs. of K2O per acre | 30 lbs. of K2O per acre | 15 lbs. of K2O per acre | 0 lbs. of K2O per acre |

2,401-2,900 lbs. per acre | 90 lbs. of K2O per acre | 65 lbs. of K2O per acre | 35 lbs. of K2O per acre | 20 lbs. of K2O per acre | 0 lbs. of K2O per acre |

2,901-3,300 lbs. per acre | 110 lbs. of K2O per acre | 75 lbs. of K2O per acre | 40 lbs. of K2O per acre | 25 lbs. of K2O per acre | 0 lbs. of K2O per acre |

3,300+ lbs. per acre | 115 lbs. of K2O per acre | 80 lbs. of K2O per acre | 45 lbs. of K2O per acre | 25 lbs. of K2O per acre | 0 lbs. of K2O per acre |

Research trials conducted in Minnesota have shown that other nutrients are not needed in a fertilizer program for sunflower production.

**CAUTION!** Do not apply more than 10 lb N + K_{2}O per acre in contact with the seed. Do not place ammonium thiosulfate (12-0-0-26) in direct contact with the seed. Do not place fertilizers containing boron in direct contact with the seed.

Reviewed in 2018