Recommended: 12,000-16,000 Plants per Acre, Based on UNL Research

March 8, 2012

Encouraged by good crop prices and rainfall in recent years, Panhandle farmers have been growing more dryland corn. While research-based, planting recommendations have long been available for eastern and central Nebraska, until recently they hadn't been updated for western Nebraska dryland conditions.

In the late 1990s, when corn acres were first starting to increase (see box), farmers wondered what population to plant. Work by UNL agronomy specialists Gail Wicks and Bob Klein in North Platte in the 1970s and ‘80s suggested 10,000 to 12,000 plants per acre for the Panhandle. However, work done in the 1990s in northeast Colorado suggested 16,000 plants per acre. To find the right answer, in 1999 we put out four studies: one each in Cheyenne, Kimball, Banner, and Box Butte counties. The Cheyenne County study was conducted at UNL’s High Plains Ag Lab north of Sidney.

Based on this research and computer modeling, my current recommendation is to plant between 12,000 and 16,000 plants per acre. This is based on several factors as described below.

Each of the 1999 studies consisted of five plant populations (7,000, 11,000, 15,000, 19,000, and 23,000 plants per acre) and five nitrogen fertility rates (0, 30, 60, 90, and 120 lb nitrogen per acre). Excellent summer rainfall in 1999 resulted in a linear increase in yield with increasing plant population. In other words, the highest yields were achieved at 23,000 plants per acre at all locations except Kimball County, where a shallow soil profile resulted in no increase in yield above 11,000 plants per acre.

To say the least, this was unexpected.

Ups and Downs —
Panhandle Dryland Corn Acreage

The number of dryland corn acres in western Nebraska has ranged from 10,000 in 1995 (prior to the 1996 Farm Bill), to a high of about 96,000 acres in 2000, the beginning of the eight-year drought. By 2005, dryland corn acreage had fallen to just 22,000 acres, but is now increasing and was at 93,000 acres in 2011.  This year, with continued strong corn prices, dryland corn acres in the Panhandle could exceed 100,000 for the first time.

We repeated the study in 2000 and got quite a different response. Unlike 1999, the summer of 2000 was very dry. Two of the four sites had a linear decrease in yield as plant population increased. The yield at these two sites (Kimball and Banner counties) was maximized at 7,000 plants per acre. Yield was maximized at 11,000 and 15,000 plants per acre at Box Butte and Cheyenne counties, respectively.

After two years of research the dilemma was what to recommend to growers: 23,000 or 7,000 plants per acre? We needed more research and more results.

Modeling Provides More Information and Leads to a Recommendation

The question was resolved following five months of work with the Agricultural Productions Systems Research Unit and the APSIM crop simulation model in Toowoomba, Queensland, Australia.  Like western Nebraska, the weather in Queensland is highly variable. The government invested in developing crop simulation models to help deal with the variation.

Using the 1999 and 2000 Nebraska data to calibrate and validate the model for Nebraska conditions, we used 48 years of historical weather data for Sidney to simulate corn yields at various plant populations.

Simulations compared results with three levels of available soil water at planting: 3.1, 6.3, or 9.4 inches in the top 5 feet of a loam soil, representing one-third, two-thirds, and full soil water profiles, respectively. Median yields (half of the yields are greater than the median and half are less) were maximized at 8,000, 12,000, and 16,000 established plants per acre for each of those three water levels. Median yields were greatest at the 9.4-inch level; however, perhaps the greater benefit of additional soil water at planting was a reduced risk of financial loss.

Factors Affecting Seeding Rate

Based on this research, my current recommendation for dryland corn in the Panhandle is to plant 12,000 to 16,000 plants per acre, depending on soil water at planting, the amount of crop residue, and a grower’s individual tolerance for risk.

Corn does best with at least 4,000 pounds of crop residue per acre. If crop residues are low, consider planting fewer plants per acre than the soil water would suggest. Historical weather records for the Nebraska Panhandle suggest that the years with good late-summer rainfall are outnumbered by years with low late-summer rainfall. So planting closer to 12,000 plants per acre may be the best option over the long run, but this rate won't provide top yields in years with good late-summer rainfall.

Final dryland corn yields are highly dependent on rainfall from flowering through the first six weeks of grain fill, but knowing the amount of soil water at planting and adjusting the plant population accordingly, will help growers manage the risk of growing this crop without irrigation.

Drew Lyon
Dryland Cropping Systems Specialist, Panhandle REC