December, 1998
Field Crops 28.31-21

The Wisconsin Comparative Relative Maturity (CRM) System for Corn

Joe Lauer, Corn Agronomist

Successful corn production requires the selection of the correct hybrids for the production environment. Farmers need to consider yield potential, maturity, pest resistance, and harvestability when selecting hybrids. Proper maturity is important so that the amount of drying necessary after harvest is minimized. High-yielding hybrids whose maturities take full advantage of the available growing season are generally the most energy-efficient choices. A hybrid which matures far in advance of anticipated harvest does not make full use of available solar radiation, and therefore does not realize the full yield potential of the growing season and the energy related inputs provided by the farmer. Conversely, a hybrid that is not mature at the time of frost can increase artificial drying costs, in addition to not achieving full yield potential because it was killed before grain filling was complete.

Field drying of corn is a little understood process that greatly influences production costs. Drying corn after harvest is expensive. Assuming LP gas costs $0.70 per gallon and electricity costs $0.05 per kilowatt hour, drying corn from 35 percent harvest moisture to 15 percent requires about 0.472 gallons LP gas per bushel and 0.066 kwh per bushel for a total cost of $0.334 per bushel (Eckert et al., 1987). Harvesting grain at 20 and 25 percent moisture is often cited as a reasonable compromise between drying costs and harvest loss (Olson and Sander, 1988). Drying corn from 20 to 25 percent harvest moisture to 15 percent requires 0.109 to 0.219 gallon of LP gas per bushel and 0.017 to 0.033 kwh per bushel for a total cost of $0.077 to $0.155 per bushel. If 350 million bushels of corn in Wisconsin were harvested between 20 and 25 percent moisture, drying costs would range between $27 to $54 million. A more likely scenario is one-third of the corn at 20 to 25 percent moisture, one-third at 25 to 30 percent moisture, and one-third at 30 to 35 percent moisture. Drying costs for Wisconsin producers under this scenario range between $55 and $85 million.

These costs do not consider yield and quality losses due to hybrids that do not take advantage of the available growing season. In addition, if the moisture content of corn taken to market is more than 15.5 percent (the maximum for No. 2 corn), then the price paid for that corn will be adjusted downward by the prevailing moisture discount which is usually around 2 percent of market price for each point above 15.5 percent.

Producers need to choose high-yielding hybrids that are dry as practical at harvest. Many shorter-season hybrids approach yields of full-season hybrids and may be several points lower in grain moisture at harvest. Some hybrids dry down more rapidly after maturity (black layer) than others of similar maturity due to loose husks, small cobs and/or thin seed coats.

The problem for farmers is accurately determining corn hybrid maturity and harvest moisture ratings between and within seed companies. The corn hybrid seed industry has no standard for maturity ratings, and will often market the same hybrid with different maturity ratings. The development of a method to determine corn hybrid maturity would allow producers to more precisely match hybrids to the length of the growing season in their production environment. In Wisconsin, there are no regulations concerning labeling of corn for maturity. The only state that regulates maturity labeling of corn hybrids is Minnesota Beginning in 1999 the Wisconsin Corn Hybrid Performance Trial program will report comparative relative maturity ratings (CRM). The approach that will be used is described in Figure 1. The grain moisture for each hybrid will be measured in three replications of a trial. The relationship between the company maturity rating and measured grain moisture is calculated using a quadratic regression model. The model uses the hybrid average moisture for "x" and solves for comparative relative maturity, "y". For example, a hybrid that was measured at 26% moisture would be rated at 109 CRM.

Two rating systems can be used for basing maturity. The industry standard for the northern tier of states in the U.S. is the Minnesota Relative Maturity rating system, which requires that all hybrids marketed in MN must be tested for maturity. Unfortunately, not all hybrids commercially available to farmers in other states are tested in the MN system. Table 1 shows some examples of hybrids tested over years in the Hybrid Trials using MN RM as the maturity basis.

In Wisconsin, company ratings will be used to calculate CRM each year. The result is an average relative maturity comparison among commercially available hybrids at the same grain moisture. Table 2 shows company RM, Minnesota RM, and Wisconsin CRM ratings for the 1998 Wisconsin Corn Hybrid Performance Trial program.

Figure 1. Method for determining Wisconsin comparative relative maturity (CRM) using company ratings.

Table 1. Examples of hybrid maturity ratings calculated in different years using WI Corn Hybrid Performance Trial data.
Brand Entry	Year	WI CRM
Dekalb DK493	1993	99
	1994	99
	1995	100
	1996	101
	1997	101
	1998	98
Golden Harvest H2441	1992	104
	1993	105
	1994	105
	1995	107
	1996	105
	1997	105
Jung 2496	1989	98
	1990	101
	1991	100
	1992	101
	1993	100
	1994	99
	1995	100
Nk Brand N4242	1991	99
	1992	101
	1993	99
	1994	99
	1995	101
	1996	99
	1998	99
Pioneer 3751	1989	97
	1990	97
	1991	99
	1992	100
	1993	99
	1998	97
CRM based on Minnesota Relative Maturity ratings.