Nitrogen guidelines
Nitrogen (N) fertilization is an important management practice for optimum production of buckwheat. Nitrogen fertilizer guidelines can be based either on the results of the soil NO3--N test or the consideration of the combination of expected yield, previous crop, and soil organic matter content. The soil NO3--N test is appropriate for western Minnesota. When the soil NO3--N test is used, the fertilizer N guidelines are calculated as follows:
Nitrogen fertilizer formula
Suggested N in lb/acre = (0.0458) (EY) - STN(0-24 in.) - Npc
Nitrogen formula variables
- EY = expected yield (lb./acre)
- STN = nitrate-nitrogen (NO3--N) measured to a depth of 24 in. (lb./acre)
- Npc = amount of N supplied by the previous legume crop (lb./acre)
For most production situations, the N fertilizers should be broadcast and incorporated before planting. The N fertilizer can be applied in either dry or liquid form. There is no research to document that one form is superior to the other.
Nitrogen guidelines for buckwheat* in pounds per acre
| Crop grown last year | Organic matter level** | 1200-1450 lb/acre | 1451-1700 lb/acre | 1701-1950 lb/acre | 1951-2200 lb/acre |
|---|---|---|---|---|---|
| Alfalfa (4+ plants/ft2) | Low | 0 lb N/acre | 0 lb N/acre | 0 lb N/acre | 0 lb N/acre |
| Alfalfa (4+ plants/ft2) | Medium/High | 0 | 0 | 0 | 0 |
| Soybeans or alfalfa (1 or less plants/ft2) | Low | 0 | 10 | 20 | 30 |
| Soybeans or alfalfa (1 or less plants/ft2) | Medium/High | 0 | 0 | 0 | 0 |
| Edible beans, field peas | Low | 20 | 30 | 40 | 50 |
| Edible beans, field peas | Medium/High | 0 | 10 | 20 | 30 |
| Group 1 Crops | Low | 0 | 0 | 0 | 0 |
| Group 1 Crops | Medium/High | 0 | 0 | 0 | 0 |
| Group 2 Crops | Low | 40 | 50 | 60 | 70 |
| Group 2 Crops | Medium/High | 20 | 30 | 40 | 50 |
*in situations when the soil NO3--N test is not used based on expected yield of the crop.
**low = less than 3.0%; medium and high = 3.0% or more
- Crops in group 1: Alsike clover, birdsfoot trefoil, grass/legume hay, grass legume pasture, fallow, 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, wheat.
Suggested nitrogen credits for crops that might precede wheat in a crop rotation*
| Previous crop | First year N credit (lb N/acre) |
|---|---|
| Soybean | 20 |
| Edible beans, field peas | 10 |
| Harvested sweet clover | 10 |
| Harvested alfalfa** or non-harvested sweet clover | |
| 4-5 plants/ft2 | 75 |
| 2-3 plants/ft2 | 50 |
| 1-2 plants/ft2 | 25 |
| 1 or fewer plants/ft2 | 0 |
| Harvested red clover | 35 |
| Sugar beet | |
| Yellow leaves at harvest | 0 |
| Light-green leaves at harvest | 15-30 |
| Dark-green leaves at harvest | 60-80 |
*Use these credits when the soil nitrate test is used.
**If 3rd or 4th cutting was not harvested, add 20 lb. N/acre to the N credits listed.
Suggested nitrogen credits when wheat is grown 2 years after a legume crop
| Previous legume crop | Second year N credit (lb N/acre) |
|---|---|
| Alfalfa (4+ plants/ft2) | 35 |
| Non-harvested sweet clover | 35 |
| Alfalfa (2-3 plants/ft2) | 25 |
| Birdsfoot trefoil | 25 |
| Red clover | 20 |
Phosphate and potash guidelines
These fertilizers, when needed, should be broadcast and incorporated before planting. Special sources of phosphate and potash are not needed for buckwheat production. Phosphorus guidelines are given for the Bray-P1 and Olsen soil test methods. The Olsen soil test should be used in situations where soil pH is greater than 7.4.
Recommendations suggest pounds of actual nutrient needed to be applied and do not reflect pounds of product that should be applied.
Pounds of product to apply needs to be calculated based on the amount of nutrient suggested divided by the percentage of P2O5 or K2O per pound in the material to be applied.
All commonly sold sources for each nutrient are equal. There is no research suggesting that nutrients other than N, P and K are needed in a fertilizer program for buckwheat production in Minnesota.
CAUTION: Do not apply any fertilizer in contact with buckwheat seed at planting.
Phosphate fertilizer guidelines*
| Expected Yield Bray-P1 Expected Yield Olsen |
0-5 ppm 0-3 ppm |
6-10 ppm 4-7 ppm |
11-15 ppm 8-11 ppm |
16-20 ppm 12-15 ppm |
21+ ppm 16+ ppm |
|---|---|---|---|---|---|
| 1200-1450 lb/acre | 35 lb/acre | 20 lb/acre | 15 lb/acre | 0 lb/acre | 0 lb/acre |
| 1200-1450 lb/acre | 35 | 20 | 15 | 0 | 0 |
| 1451-1700 lb/acre | 40 | 25 | 15 | 0 | 0 |
| 1701-1950 lb/acre | 45 | 30 | 20 | 0 | 0 |
| 1951-2200 lb/acre | 50 | 35 | 20 | 0 | 0 |
*Pounds of P2O5 suggested to apply per acre for buckwheat production based on either the Bray-P1 or Olsen soil methods test reported in parts per million (ppm). Use one of the following equations if a phosphate guideline for a specific soil test and a specific expected yield is desired:
- P2O5 rec = [0.0275 - (0.0014) (Bray P, ppm)] (Expected Yield)
- P2O5 rec = [0.0275 - (0.0017) (Olsen P, ppm)] (Expected Yield)
Potash fertilizer guidelines*
| Expected Yield | 0-40 ppm | 40-80 ppm | 80-120 ppm | 120-160 ppm | 160+ ppm |
|---|---|---|---|---|---|
| 1200-1450 lb/acre | 45 lb/acre | 35 lb/acre | 20 lb/acre | 0 lb/acre | 0 lb/acre |
| 1451-1700 lb/acre | 55 | 40 | 25 | 0 | 0 |
| 1701-1950 lb/acre | 60 | 45 | 25 | 10 | 0 |
| 1951-2200 lb/acre | 70 | 50 | 30 | 10 | 0 |
*Pounds of K2O suggested to apply per acre for buckwheat production based on the ammonium acetate potassium test reported in parts per million (ppm). Use the following equation if a potash guideline for a specific soil test and a specific expected yield is desired.
- K2O rec = [0.0358 - (0.023) (Soil Test K, ppm)] (Expected Yield)
Reviewed in 2023