Handling Corn in an "Emergency" Forage Season: Agronomic and Economic Considerations

July 1, 2004  11(17):116-117

Joe Lauer, Corn Agronomist  

An "emergency" forage situation occurs when farmers have abandoned hope for grain production and use a crop only for its stover (leaves and stalks). Grain yield is usually not possible or minimal due to late planting and the amount of growing season remaining. In Wisconsin corn grain production is minimal after June 20. After June 20, corn should only be considered if it is a forage "emergency." This article will discuss some of the agronomic and economic factors that should be considered for farmers choosing corn for forage.

How late can corn planting occur?

Corn at the V12 stage is similar in height to small grains. To achieve the V12 stage of growth 815 GDUs are required. At Arlington GDU accumulation between August 1 and the average killing frost date of October 7 is 1000 GDUs. Corn at V12 can yield 20% of a normal crop or about 1.5 to 2 T dry matter/A (Ritchie et al., 1993) with 15% of the dry matter in leaves. 

Soil Fertility

This year the N loss processes that occur with wet conditions have reduced inherent soil N levels and the soil's ability to contribute N for plant needs. In an emergency situation, using starter fertilizer (10-20-20) will help corn plants grow faster. Since corn forage yield will be reduced, N rates can be reduced, but corn is a N-responsive plant, so some N will be required. At least 40 to 50 lbs N/A should be applied when producing corn as emergency forage (Bundy, personal communication). No N may be needed for corn following alfalfa.

Plant density

Corn forage yield increases with increasing plant density, but the trade-off is that corn forage quality decreases. In an emergency situation where only stover is produced, quality is most influenced by hybrid maturity and frost-kill date, so one need not be overly concerned about the trade-off between plant density and quality. Plant densities of 40 000 to 50 000 plants/A would be recommended for emergency corn forage.

Row spacing

Little data exists for corn response to row spacing when late-planted. Using typical planting dates, corn forage yield increases 7 to 9 % as row spacing decreases from 30 to 15 inches. A slightly smaller yield response would be expected with emergency conditions since no grain yield would be produced.

Since corn forage responds to higher plant density and to further reduce production costs, a grain drill might be considered. Applying starter fertilizer will be difficult and correct calibration of the drill will be important, as small changes in the seed meter will result in large plant density changes.

Pest Control

It is usually easier to control weeds in late corn plantings than in early plantings.  Late tillage kills many germinated weeds and corn seedlings are more competitive due to warmer temperatures. 

Insects normally are a greater threat to late plantings than weeds.  Use a seed treatment for seed corn maggot since 4 to 5 generations can hatch over the growing season. No soil rootworm insecticide will need to be applied, since the corn rootworm hatch is usually complete by mid-June and the larvae die within 48 hours if no corn roots are present (Jensen, personal communication). Scout for cutworm and second-generation European corn borers.

Cost of Production

Acre cost of production for emergency corn forage would be lower than normal corn forage, but more expensive on a per unit yield basis. Corn forage planted on July 1 could reasonably be expected to yield 4 T dry matter/A.

Cost savings could occur with soil fertility, pest control, and equipment (if a grain drill is used). Seed costs would increase slightly if higher plant density was used. Lower yields would in turn reduce chopping and hauling costs. Input savings for emergency corn forage production of $20 to $60 might be reasonably expected.

Average cost of production for corn grain in the PEPS Cash and Livestock program is $277 to $225 per A (1994-2003). Budget estimates for corn forage production of 6 T dry matter/A are slightly higher ranging from $287 to $361 per A or $48 to $60 per T dry matter.

With projected savings of $40 per A and a yield level of 4 T dry matter/A, emergency corn forage would cost $62 to $80 per T dry matter, which is about $14 to $20 per T dry matter higher than normal corn forage.  Forage quality of emergency forage would be only slightly lower than normal corn forage quality.

Literature Cited

Ritchie, S. W., J. J. Hanway, and G. O. Benson. 1993.  How a corn plant develops. Iowa State University CES Special Report No. 48.  21 pp.

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