Illinois Farmer Today
A cold and wet March in many areas gave us time to think about issues related to planting and early-season management.
Should we start planting soybeans or corn first?
The forecast is for warmer and a little drier conditions moving into April. If that holds, it makes little difference which crop gets planted first — the decision can simply be based on which fields are ready first.
If it stays warm without heavy rainfall after planting, both crops will get off to a good start and benefit equally. Prolonged cool temperatures following very early planting of both corn and soybeans can limit yield potential, although this is rare. If the forecast changes to cooler and wetter, neither crop will have much advantage: Corn emerges a little better than soybeans under such conditions, but this is offset by the need to have a higher percentage of corn seeds emerge.
Planting date responses measured as percentage of maximum yield are similar for both crops, and as we have seen in recent years, even late-planted crops can yield well if the growing season is favorable.
Even though planting early helps crops get off to a good start if the weather cooperates, planting date has less influence on yields than the weather during the warm months of the growing season.
Does automated depth or down-pressure adjustment improve stands and yields?
For fields that have produced excellent stands and high yields without these features, probably not. In Illinois, it is rare that loam-textured or heavier soils are dry enough at planting to limit germination of corn or soybean seed planted at normal depths (1.25 to 2 inches).
Planting deep enough to place seeds into sensed moisture — a feature of some systems — sounds promising, but the advantage of doing this compared to uniform depth placement is not clear, especially if the topsoil has moisture, which is often the case. Most planting depth studies show that planting 3 inches deep lowers yield, and if an automated system can and does place seed that deep, it could cause harm.
Down-pressure adjustment capability assists in getting proper planting depth, and also in controlling how much “row compaction” there is. It may have value for no-till planting into dry soils, but perhaps less value for planting into tilled seedbeds.
The most important planting objectives include getting seeds placed at proper depth, reasonable spacing uniformity, and good seed-soil contact to help water move into the seed for germination. Most modern, well-maintained planters do this very well in most soils, without add-ons.
Have optimum seeding rates changed?
Corn plant populations have not continued to increase as much as many of us once thought they would. In large part that’s because hybrids have added more yield per plant, without needing more plants.
In studies, 34,000 to 38,000 plants per acre often maximizes yield. Planting 42,000 to 45,000 seeds usually does not lower yields compared to planting 36,000 to 40,000, but the added cost of seed is not covered by the average increase in yield.