Soybeans can be planted at varying seeding rates because growers know that different rates within an acceptable range can be used without affecting yield potential. Seed of today's biotech varieties often cost more than $30 per 50 pounds. Thus, the seeding rate decision now has significant economic implications.

Information in the accompanying table can be used to determine how much a particular seeding rate will cost, and how much a change in seeding rate will affect cost.

For instance, if seed cost is $30 per 50 pounds, increasing seeding rate of a 3,000-seeds-per-pound variety from 120,000 to 160,000 seeds per acre will increase cost $8 per acre when 50 pounds are planted.

If there is no agronomic reason to use the higher seeding rate, the extra seed cost will reduce net return.

On the other hand, producers may decide that the extra cost is worth the peace of mind gained from planting on the higher end of the range to ensure an acceptable stand in a planting environment that is less than ideal.

Planting the same number of seeds per acre of comparably performing varieties with a different number of seeds per pound will affect cost.

For instance, planting 140,000 seeds of a variety with 3,000 seeds per pound will cost over $4.50 per acre more than planting the same number of seeds of a variety with 3,600 seeds per pound. If the two varieties are comparable in performance, then this higher cost will reduce net income.

Producers should use their prior seeding rate experience to make an economical seeding rate decision.

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Larry G. Heatherly is a retired USDA-ARS research agronomist and current crop consultant. e-mail larryheatherly@bellsouth.net

Number of seeds per foot of row and cost per acre for soybean seed of varied size and cost planted at different seeding rates in five row spacings.

			Row spacing — inches					Cost/50 lb. of seed
Seed size	Seeding rate		7	15	20	30	40	$15	$20	$25	$30
No./lb.	seeds/acre	lb./acre	No. seed/ft. of row					$/acre
2800	100,000	35.7	1.3	2.9	3.8	5.7	7.7	10.71	14.29	17.86	21.43
	120,000	42.8	1.6	3.4	4.6	6.9	9.2	12.86	17.14	21.43	25.72
	140,000	50.0	1.9	4.0	5.4	8.0	10.7	15.00	20.00	25.00	30.00
	160,000	57.1	2.1	4.6	6.1	9.2	12.2	17.14	22.86	28.57	34.28
	180,000	64.3	2.4	5.2	6.9	10.3	13.8	19.29	25.71	32.14	38.57
	200,000	71.4	2.7	5.7	7.6	11.5	15.3	21.43	28.57	35.71	42.85
3000	100,000	33.3	1.3	2.9	3.8	5.7	7.7	10.00	13.33	16.67	20.00
	120,000	40.0	1.6	3.4	4.6	6.9	9.2	12.00	16.00	20.00	24.00
	140,000	46.7	1.9	4.0	5.4	8.0	10.7	14.00	18.67	23.33	28.00
	160,000	53.3	2.1	4.6	6.1	9.2	12.2	16.00	21.33	26.67	32.00
	180,000	60.0	2.4	5.2	6.9	10.3	13.8	18.00	24.00	30.00	36.00
	200,000	66.7	2.7	5.7	7.6	11.5	15.3	20.00	26.67	33.33	40.00
3200	100,000	31.2	1.3	2.9	3.8	5.7	7.7	9.38	12.50	15.63	18.76
	120,000	37.5	1.6	3.4	4.6	6.9	9.2	11.25	15.00	18.75	22.50
	140,000	43.8	1.9	4.0	5.4	8.0	10.7	13.13	17.50	21.88	26.25
	160,000	50.0	2.1	4.6	6.1	9.2	12.2	15.00	20.00	25.00	30.00
	180,000	56.2	2.4	5.2	6.9	10.3	13.8	16.88	22.50	28.13	33.76
	200,000	62.5	2.7	5.7	7.6	11.5	15.3	18.75	25.00	31.25	37.50
3400	100,000	29.4	1.3	2.9	3.8	5.7	7.7	8.82	11.76	14.71	17.66
	120,000	35.3	1.6	3.4	4.6	6.9	9.2	10.59	14.12	17.65	21.18
	140,000	41.2	1.9	4.0	5.4	8.0	10.7	12.35	16.47	20.59	24.71
	160,000	47.0	2.1	4.6	6.1	9.2	12.2	14.12	18.82	23.53	28.24
	180,000	52.9	2.4	5.2	6.9	10.3	13.8	15.88	21.18	26.47	31.77
	200,000	58.8	2.7	5.7	7.6	11.5	15.3	17.65	23.53	29.41	35.28
3600	100,000	27.8	1.3	2.9	3.8	5.7	7.7	8.33	11.11	13.89	16.66
	120,000	33.3	1.6	3.4	4.6	6.9	9.2	10.00	13.33	16.67	20.00
	140,000	38.9	1.9	4.0	5.4	8.0	10.7	11.67	15.56	19.44	23.33
	160,000	44.4	2.1	4.6	6.1	9.2	12.2	13.33	17.78	22.22	26.67
	180,000	50.0	2.4	5.2	6.9	10.3	13.8	15.00	20.00	25.00	30.00
	200,000	55.6	2.7	5.7	7.6	11.5	15.3	16.67	22.22	27.78	33.33