Due to recent rain and snow, only 2 percent of Minnesota’s corn had been planted by April 28, similar to 2018 but 15 days behind the 5-year average, according to the USDA National Ag Statistics Service. This article addresses the effects of delayed planting on corn yield potential and key considerations for growers.
Planting date and corn yieldPlanting date is only one of several factors influencing corn yield. Other factors, including stand establishment, weather conditions during the two weeks before and two weeks after tasseling, hybrid selection, crop nutrition, weed and pest control, and crop rotation, typically carry more weight. Field trials conducted by the University of Minnesota show that on average, corn yield is within 2 percent of the maximum when planting occurs between April 20 and May 10 or 15, within 5 percent of the maximum when planting occurs by May 15 to 20, and within 8 percent of the maximum when planting occurs by May 20 to 25. However, many would not consider this year’s spring weather to be representative of the average during the past few years.
Since mid-April of this year, growing degree day (GDD) accumulation has been negligible and suitable field conditions for planting have been limited in frequency and duration. University of Minnesota research indicates little to no loss in corn yield potential until around 115 GDDs have accumulated between the first feasible planting opportunity after mid-April and when a field is planted.
Plant when soil conditions are suitablePreplant tillage and planting when soil conditions are suitable is key for successful stand establishment. Potential advantages to an earlier planting date can be negated if preplant tillage and planting occur when soils are too wet.
A field is ready for seedbed preparation when soil in the depth of tillage crumbles when squeezed. Tillage in wet soil causes clods, which reduce seed-to-soil contact. Excellent seed-to-soil contact is essential for rapid imbibition (uptake) of moisture by seeds and uniform emergence. Tillage in wet soil also creates a compacted layer below the depth of tillage, which can restrict root development.
Sidewall compaction can occur when planter disc openers cut through wet fine-textured soil, resulting in compacted soil around the seed that is difficult for roots to penetrate. This can restrict root development, nutrient and water uptake, and crop growth. Seed furrows can also open after planting in such conditions, resulting in poor seed-to-soil contact.
Soil temperatureGermination of corn requires that seeds imbibe 30 percent of their weight in water and that soil temperature be 50°F or warmer. Risk of inadequate stand establishment is reduced if corn is planted when soil in the seed zone has reached or is near 50ᵒF and is expected to warm, since imbibition of water by seed is not influenced by soil temperature. However, when planting is delayed until May in the upper Midwest, planting should generally begin as soon as soil conditions are suitable, regardless of soil temperature.
Although infrequent, imbibitional chilling injury to corn can occur when soil temperature is near 40°F or lower within 24 to 48 hours of corn planting and seeds imbibe cold water to start the germination process. This is because cellular tissues of seeds are less flexible under cold conditions and can rupture when seeds swell due to imbibition of water. Beyond 48 hours after corn planting, the risk of imbibitional chilling injury is greatly reduced.
Hybrid maturityIf corn planting is delayed until after the first three weeks of May, switching full-season hybrids to earlier-maturity hybrids reduces the risk of corn freezing in the fall before it has reached maturity. In such instances, planting hybrids that are 5 to 7 or more relative maturity units earlier than those considered full-season reduces the risk of corn being froze in the fall prior to maturity.
Planting grain corn after May 31 carries high risk in Minnesota. However, decisions regarding the crop to plant can be influenced by factors such as fertilizer applied and seed availability. If grain corn is planted after May 31 in Minnesota, growers can reduce risk by planting hybrids that are 15 or more relative maturity units earlier than full-season hybrids.