Buckwheat

Daniel E. Kaiser, Extension Soil Scientist; John A. Lamb, Extension Soil Scientist; and Roger Eliason, Director, University of Minnesota Soil Testing Laboratory

Revised 2011

Nitrogen

Figure 1. The fall soil nitrate test should be used for nitrogen recommendations in the counties that are shaded.

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 (see Figure 1). When the soil NO₃^--N test is used, the fertilizer N guidelines are calculated as follows:

N_rec = (0.0458) (EY) - STN_{(0-24 in.} - N_Pc

Where:

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).
These N credits are summarized in Table 1.

The N fertilizer guidelines for production situations where the soil NO₃^--N test is not used are listed in Table 2.

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.

Table 1. Nitrogen credits for various legume crops that might precede barley in a crop rotation. Use these credits for the "N_pc" factor in situations where the soil nitrate test is used.

Previous Crop	1st Year Nitrogen Credit
	lb. N/acre
Soybean	20
Edible beans, field peas	10
Harvest sweetclover	10
Harvested alfalfa*
4 to 5 plants/ft²	75
2 to 3 plants/ft²	50
1 or fewer plants/ft²	0
Harvested red clover	35

* Add 20 lb. N/acre to the credits listed if the 3rd or 4th cutting was not harvested.

Table 2. Nitrogen guidelines for buckwheat in situations when the soil NO₃^--N test is not used.

	Expected Yield (bu./acre)
Crop Grown Last Year	Organic Matter Level*	1200-1450	1451-1700	1701-1950	1951-2200
Alfalfa (4+ plants/ft²)	Low Med and high	0 0	0 0	0 0	0 0
Soybeans Alfalfa (1 or less plants/ft²)	Low Med and high	0 0	10 0	20 0	30 0
Edible beans, field peas	Low Med and high	20 0	30 10	40 20	50 30
Group 1 Crops	Low Med and high	0 0	0 0	0 0	0 0
Group 2 Crops	Low Med and high	40 20	50 30	60 40	70 50

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

Therefore, all sources of N are equal if properly applied.

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 and Potash

The guidelines for the use of phosphate and potash are summarized in Tables 3 and 4.

These fertilizers, when needed, should be broadcast and incorporated before planting. Special sources of phosphate and potash are not needed for buckwheat production. All commonly sold sources for each nutrient are equal.

There is no research which suggests 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.

Table 3. Phosphate fertilizer guidelines for buckwheat production.

		Phosphorus (P) Soil Test, ppm *
Expected Yield	Bray:	0-5	6-10	11-15	16-20	21 +
Expected Yield	Olsen:	0-3	4-7	8-11	12-15	16 +
1200-1450		35	20	15	0	0
1451-1700		40	25	15	0	0
1701-1950		45	30	20	0	0
1951-2200		50	35	20	0	0

* Use one of the following equations if a phosphate guideline for a specific soil test and a specific expected yield is desired.

P₂O_{5 rec} = [0.0275 – (0.0014) (Bray P, ppm)] (Expected Yield)
P₂O_{5 rec} = [0.0275 – (0.0017) (Olsen P, ppm)] (Expected Yield)

Table 4. Potash fertilizer guidelines for buckwheat production.

Expected Yield	Potassium (K) Soil Test, ppm *
Expected Yield	0-40	40-80	80-120	120-160	160 +
lb./acre	— K₂O to apply (lb.acre) —
1200-1450	45	35	20	0	0
1451-1700	55	40	25	0	0
1701-1950	60	45	25	10	0
1951-2200	70	50	30	10	0

* Use the following equation if a potash guideline for a specific expected yield.

K₂O rec = [0.0358 – (0.023) (Soil Test K, ppm)] (Expected Yield)

Fertilizer Recommendations for Agronomic Crops in Minnesota