Thin soybean stands can produce surprisingly high yields

Contact: Eric Anderson<eander32@msu.edu>, Michigan State University Extension - May 29, 2019

Updated from an original article written by Eric Anderson.

Consider this information when making soybean replant decisions.

Plant stands from 80,000 seeds per acre planting rate. See side-by-side comparison pictures below of 80,000 versus 160,000 seeds per acre panting rate. All photos by Mike Staton, MSU Extension.

When poor soybean emergence and thin stands occur, producers are compelled to make timely and informed replant decisions. Accurately, assessing your soybean stand and diagnosing the cause of the emergence problems are the first steps in the process. Once the existing stand has been determined, use the information provided in this article to help inform replant decisions.

The final plant stands and yields of the lowest and the highest planting rates from 39 planting rate trials conducted in Michigan in 2015, 2016, 2017 and 2018 are compared in Tables 1, 2, 3 and 4, respectively. The detailed information from all the planting rate trials conducted from 2015 to 2018 is available in the 2017 and 2018 SmaRT On-farm Research Reports. Information provided in the following tables clearly shows that thin soybean stands can produce surprisingly high yields.

However, there were exceptions as yields from the 80,000 planting rate were reduced by more than 4 bushels per acre at nine of the 39 sites (23 percent of the time). Four bushels per acre is the breakeven yield loss for the 80,000 planting rate given current seed and crop prices. At three of these sites, the yield loss was more than 7 bushels per acre. It should be noted that none of the varieties planted in the trials were thin or straight-line plant types.

Table 1. Effect of low soybean planting rates on final plant stand and yield in 2015.
Location	Row width	Planting date	Target planting rate (seeds/ac)
			80,000		160,000
			Stand (plants per acre)	Yield (bushels per acre)	Stand (plants per acre)	Yield (bushels per acre)
Cass 1	15”	13-May	79,100	48.9	133,100	54.5
St. Joseph	Twin 8”	29-Apr	69,800	63.8	138,100	64.7
Tuscola	15”	21-May	54,500	60.1	126,600	59.1
Sanilac 1	30”	21-May	63,200	52.7	138,400	53
Sanilac 2	15”	5-May	71,600	63.2	136,200	57.9
Berrien	30”	22-May	78,500	72.1	150,600	75.9
Cass 2	15”	14-May	78,300	72	150,000	72.4
Monroe	15”	9-May	51,500	38.9	105,800	49.8
Ingham	Twin 7”	13-May	79,900	46.5	180,000	47.6
Fairgrove	28”	19-May	73,300	65.8	151,300	66.6
Average			70,000	58.4	141,300	60.2

Table 2. Effect of low soybean planting rates on final plant stands and yield in 2016.
Location	Row width	Planting date	Target planting rate (seeds per acre)
			80,000		160,000
			Stand (plants per acre)	Yield (bushels per acre)	Stand (plants per acre)	Yield (bushels per acre)
Tuscola 1	15”	19-May	66,000	67.2	128,200	71.7
Sanilac 1	22”	21-May	77,100	80.3	149,100	79
Sanilac 2	20”	7-May	59,200	75	124,900	79.3
Tuscola 2	15”	9-May	66,600	78	118,300	80.7
Tuscola 3	15”	9-May	65,000	71.9	122,600	77.7
Sanilac 3	24”	20-May	59,800	61.6	150,900	69.2
Cass	15”	23-May	75,300	75.6	142,300	74.5
Calhoun	30”	16-May	57,300	62	115,800	64.8
Barry	30”	2-Jun	59,000	55	130,000	56.8
Ionia	15”	19-May	69,900	77	128,200	80.1
Ingham	Twin 7”	25-May	79,400	53	138,200	51.4
Average			66,800	68.7	131,700	71.4

Table 3. Effect of low soybean planting rates on final plant stand and yield in 2017.
Location	Row width	Planting date	Target planting rate (seeds/ac)
			80,000		160,000
			Stand (plants per acre)	Yield (bushels per acre)	Stand (plants per acre)	Yield (bushels per acre)
Sanilac 1	22”	19-May	71,200	61	123,100	62.2
Sanilac 2	20”	15-May	66,900	69	124,400	67.6
Tuscola 1	15”	23-May	65,000	50.8	117,600	52.5
Sanilac 3	30”	24-May	72,400	54.3	131,800	57.3
Sanilac 4	30”	31-May	73,000	36.8	155,400	42.9
Saginaw 1	15”	7-Jun	50,500	41.9	89,200	42.2
Saginaw 2	15”	7-Jun	44,000	43.0	92,500	47.2
Shiawassee	15”	15-May	61,600	42.5	131,300	45.8
Tuscola 2	15”	15-May	73,900	56.4	132,900	63.6
Calhoun	30”	8-May	59,600	44	109,300	46.4
Berrien	30”	22-May	69,800	64.2	126,500	65.2
Average			64,400	51.3	121,300	53.8

Table 4. Effect of low soybean planting rates on final plant stand and yield in 2018
Location	Row width	Planting date	Target planting rate (seeds per acre)
			80,000		160,000
			Stand (plants per acre)	Yield (bushels per acre)	Stand (plants per acre)	Yield (bushels per acre)
Tuscola	15”	May 14	64,700	66.0 b	124,200	68.5
Sanilac 1	30”	May 18	74,700	59.5	130,200	63.5
Barry 1	30”	May 8	62,800	65.3	97,900	62.5
Sanilac 2	22”	May 25	54,500	79.2	121,000	81.4
Barry 2	30”	May 8	51,500	53.9	92,300	57.7
Saginaw	30”	June 7	57,400	66.2 a	105,100	61.2
Eaton	15”	June 14	66,900	57.9 b	122,800	60.7
Average			61,800	64.0	113,400	65.1

Soybean agronomists have identified 100,000 plants per acre in narrow rows and 80,000 plants per acre in 28- and 30-inch rows as the minimum plant stands required to produce optimum yields. However, the information presented in the preceding tables shows that fields having plant stands of less than 80,000 plants per acre have the potential to produce high yields. I urge producers to consider this information when making soybean replant decisions. Producers should also consider the fact that soybean yields have been shown to decrease by 0.3 to 0.4 of a bushel per acre per day that planting is delayed after the first week of May when making replant decisions.

80,000 seeds per acre 160,000 seeds per acre

Plant stands from the 80,000 seeds per acre planting rate (left/top) and the 160,000 seeds per acre planting rate (right/bottom) from the 2017 Sanilac 2 planting rate trial.

The case for keeping reduced stands becomes even stronger for fields having a history of white mold. The lower plant stands may actually produce higher yields than higher plant stands when conditions favoring the development of white mold occur (see the Sanilac 2 site in Table 1 and the Saginaw site in Table 4). The lowest planting rate increased soybean yields by 5 bushels per acre and income by $80 per acre over the highest planting rate at these locations.

MSU Extension offers additional educational resources and programs to help farmers as they deal with delayed planting seasons at https://www.canr.msu.edu/agriculture/delayed-planting-resources.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).