Plant Populations

Pawel Wiatrak

Plant population is correlated with corn yields and should be based on soil type. Heavier soils have higher water and nutrient holding capacity than sandy soils, and have higher yield potential. Recommended populations range from 19,000 to 24,000 for sandy soils with low rainfall, 24,000 to 28,000 for heavier soils, and 28,000 to 32,000 for irrigated corn. The seeding rate should be about 10 - 15% higher than desired harvest population (Table 1).

Seeding rates will also depend on the tillage, hybrid tolerance, and standability.  It is important to remember that extremely high plant populations will lead to increased lodging, smaller ears, lower number of kernels per ear, and lower yields. Usually high-yielding grain corn hybrids produce high biomass yields. Also, there are corn hybrids developed specifically for silage.

The plant population for growing corn for silage should be 2,000 to 3,000 plants higher compared to planting a hybrid for grain. The elevated plant population increases the biomass yields and total digestable nutrient production without the risk of lodging due to earlier harvest of corn for silage. Table 2 can assist with calculating the plant stand per acre after counting the number of plants within a specific row width and length and multiplying this number by 1,000.

Table 1. Kernel spacing within the row for different planting rates and row spacings.

Seeding rate/acre Stand/acre (10% loss) Row spacing (inches)
15 20 22 28 30 36 38 40
Space between kernels (inches)
19,000 17,100 22.0 16.5 15.0 11.8 11.0 9.2 8.7 8.3
20,000 18,000 20.9 15.7 14.3 11.2 10.5 8.7 8.3 7.8
21,000 18,900 19.9 14.9 13.6 10.7 10.0 8.3 7.9 7.5
22,000 19,800 19.0 14.3 13.0 10.2 9.5 7.9 7.5 7.1
23,000 20,700 18.2 13.6 12.4 9.7 9.1 7.6 7.2 6.8
24,000 21,600 17.4 13.1 11.9 9.3 8.7 7.3 6.9 6.5
25,000 22,500 16.7 12.5 11.4 9.0 8.4 7.0 6.6 6.3
26,000 23,400 16.1 12.1 11.0 8.6 8.0 6.7 6.3 6.0
27,000 24,300 15.5 11.6 10.6 8.3 7.7 6.5 6.1 5.8
28,000 25,200 14.9 11.2 10.2 8.0 7.5 6.2 5.9 5.6
29,000 26,100 14.4 10.8 9.8 7.7 7.2 6.0 5.7 5.4
30,000 27,000 13.9 10.5 9.5 7.5 7.0 5.8 5.5 5.2
31,000 27,900 13.5 10.1 9.2 7.2 6.7 5.6 5.3 5.1
32,000 28,800 13.1 9.8 8.9 7.0 6.5 5.4 5.2 4.9
33,000 29,700 12.7 9.5 8.6 6.8 6.3 5.3 5.0 4.8
34,000 30,600 12.3 9.2 8.4 6.6 6.1 5.1 4.9 4.6
35,000 31,500 11.9 9.0 8.1 6.4 6.0 5.0 4.7 4.5
36,000 32,400 11.6 8.7 7.9 6.2 5.8 4.8 4.6 4.4

Table 2. Row spacing and row length for 1/1,000 acre.

Row spacing (inches) Row length (1/1,000 acre)
15 34 ft. 10 inches
20 26 ft. 2 inches
22 23 ft. 9 inches
28 18 ft. 8 inches
30 17 ft. 5 inches
36 14 ft. 6 inches
38 13 ft. 9 inches
40 13 ft. 1 inch