Jeff Coulter, Extension Corn Agronomist
With narrow profit margins, it is critical for dairy producers to re-evaluate agronomic practices such as planting date, plant population, and row width for corn silage production. From 1997 to 2002, corn silage planting date trials were conducted by the University of Wisconsin near Lancaster, WI, which is at similar latitude as Rochester, MN. Averaged across years, silage quality (milk per ton) was within 1% of the maximum with planting dates between April 15 and May 17. Milk per acre, however, which is a function of both milk per ton and silage dry matter yield, was within 1% of the maximum in these trials with planting dates between April 21 and May 6.
These results support research on corn grain conducted by the University of Minnesota from 1988 to 2003 at Lamberton, MN. In these trials, corn grain yield was maximized with an April 28 planting date, but planting between April 21 and May 6 produced grain yields within 1% of the maximum on average (Figure 1). For corn silage producers in central Minnesota, optimum planting dates will likely be about 4 days later. Although corn silage responds to early planting just like corn grain, the advantage to an early planting date will be negated if corn is planted when soils are too wet. This can result in compacted soil around the seed and seed furrows that open up if dry conditions follow planting.
Another important agronomic factor is plant population, especially with the high cost of seed. In general, silage dry matter yield increases with increased plant population, but increases in dry matter yield are slowed when final population is increased above 35,000 plants per acre. Milk per ton, however, decreases at a constant rate with increasing plant population. Research conducted by the University of Wisconsin indicates that the economically optimum final population for corn silage is about 1,500 plants per acre higher than that for corn grain. Between 2004 and 2008, research conducted by the University of Minnesota at Lamberton and Waseca, MN indicates that the economic optimum final population for corn grain is between 32,000 and 34,000 plants per acre, depending upon the cost of seed and price of grain. Thus, a final population between 33,500 and 35,500 plants per acre would be sufficient for optimizing milk per acre from corn silage in Minnesota. Seeding rates will need to be higher, however, to account for less than perfect emergence. Final populations above 35,500 plants per acre will likely result in less milk per acre from corn silage, since forage quality decreases with increasing plant population.
Row width is another factor to consider, especially for producers that have the ability to harvest corn silage planted in rows narrower than 30 inches. From 1997 to 1999, row width trials for corn silage were conducted at 12 sites in south-central Wisconsin at latitudes similar to Rochester, MN. In these trials, the standard row width of 30 inches was compared with 15- or 20-inch rows, depending upon location. On average, corn silage yield (adjusted to 65% moisture) was 7% greater with narrow rows. These researchers also found that forage quality was not affected by row width, that optimum plant population was similar for both 30-inch and narrow rows, and that there was no advantage to final populations above 35,000 plants per acre. Results from at least 30 other row width comparisons conducted by universities in New York and Pennsylvania are similar.
In summary, dairy producers in southern Minnesota can get the greatest return from their corn silage by planting between April 21 and May 6, having a final stand of 33,500 to 35,500 plants per acre, and using row widths narrower than 30 inches. Equipment costs, however, should be taken into account when deciding whether to plant corn in narrow rows. In order to optimize corn silage production, producers should also attempt to minimize soil compaction during silage harvest and manure application, and rotate corn with other crops when possible.
Figure 1. Response of corn grain yield to planting date between 1988 and 2003 at Lamberton, MN