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Plant population refers to the number of plants per acre; planting or seeding rate refers to the number of seeds planted per acre.The two should not be confused. Producers typically need to plant more seed than their intended plant population goal.
How much more will depend on the germination percentage of the seed being used, soil conditions, and anticipated pest problems.Tables 3 and 4 should be helpful in making planting rate and plant population measurements.
Average plant populations for the state of Iowa have shown a steady increase over the last decade. Plant populations have increased at a rate of 400 plants per acre since 1992. Much of this increase can be attributed to improved hybrids that are much more tolerant of high population stress than hybrids
used previously.
Optimum plant population depends on factors such as hybrid, moisture stress level, soil fertility, and yield goal. Each producer should adjust populations according to these factors.The optimum plant population will not only vary between regions of the state, but from season to season, and field to field on the
same farm. Data shows that optimum populations do vary across locations, but these variations are relatively small.When environmental conditions are favorable, soil fertility levels are optimized, and appropriate hybrids are selected, optimum
yields likely will occur when populations in the range of 28,000 to 32,000 plants per acre are used. Recommendations for silage production are 2,000 to 4,000 plants per acre higher than for grain production.
Table 3
Relationship between seeds planted, distance between seeds, and projected
final stand.
| |
Row spacing, inches |
|
Seeds planted |
15 |
20 |
30 |
36 |
38 |
Plant population |
(per acre) |
(inches between seeds) |
(per acre) |
24,000 |
17.4 |
13.1 |
8.7 |
7.3 |
6.9 |
20,400 |
26,000 |
16.1 |
12.1 |
8.0 |
6.7 |
6.3 |
22,100 |
28,000 |
14.9 |
11.2 |
7.5 |
6.2 |
5.9 |
23,800 |
30,000 |
13.9 |
10.5 |
7.0 |
5.8 |
5.5 |
25,500 |
32,000 |
13.1 |
9.8 |
6.5 |
5.4 |
5.2 |
27,200 |
34,000 |
12.3 |
9.2 |
6.1 |
5.1 |
4.9 |
28,900 |
36,000 |
11.9 |
8.7 |
5.8 |
4.8 |
4.6 |
30,600 |
38,000 |
11.0 |
8.3 |
5.5 |
4.6 |
4.3 |
32,300 |
40,000 |
10.5 |
7.8 |
5.2 |
4.4 |
4.1 |
34,000 |
44,000 |
9.5 |
7.1 |
4.8 |
4.0 |
3.8 |
37,400 |
*Assuming 15 percent mortality
Table 4
Method of estimating plant population.*
Row width |
Length of row |
(inches) |
(in feet equal to 1/1000th acre) |
15 |
34'10" |
20 |
26'2" |
30 |
17'5" |
36 |
14'6" |
38 |
13'9" |
*Count plants (not tillers) and multiply by 1,000 to estimate plants per acre.
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