After physiological maturity, grain must dry to a harvestable moisture. Rate of drying is affected by weather patterns, cultivar traits, and management practices. The objective of this study was to determine drying rate and test weight changes of late-developing corn, with emphasis on hybrid and planting date influences. Between 1992 and 1994, field experiments were conducted on a Plano silt loam near Arlington, WI. Five hybrids, differing in relative maturity, were planted on seven planting dates between 21 April and 22 June. After harvest, remnant field-standing plants were sampled monthly until the following spring. Test weight tended to increase with later sample dates. Hybrid differences for kernel moisture were observed on every sample date, with some hybrids drying at a greater rate than others. Early planted corn had less grain moisture than late planted corn in mid-October. The rate of kernel drydown was greater for late planted corn, with most of the drying occurring by mid-December. By mid-March, no differences were observed between early and late planted corn for kernel moisture. When corn is immature or late planted, it is best to harvest immediately in a livestock feeding situation. Under drying and storage situations, grower return of immature corn increases by letting it stand in the field.

Low grain moisture at harvest is important for profitable corn production systems. If grain moisture is high, shelling efficiency and grain quality are reduced and drying costs and shrinkage penalties increase. Corn with low grain moisture may be harvested earlier resulting in less field loss from lodging due to stalk rot and severe storms, less chance of water logged fields, and less ear drop.

The best time to harvest depends on the harvest and storage system available to the producer. Grain typically matures at 30 to 32 percent moisture (Aldrich et al., 1986). After physiological maturity, grain must dry to a harvestable moisture level. Harvesting shelled grain at 20 to 25 percent moisture is often cited as a reasonable compromise between drying costs and harvest loss (Olson and Sander, 1988). Long term storage of shelled corn should be at 13 percent moisture.

Weather characteristics influencing the rate of grain drying include vapor-pressure deficit, hours of sunshine, rate of evaporation and wind (Dodds and Pelton, 1967). Hybrid traits involving husk, ear, cob and kernel characteristics affect drying rate of corn (Sweeney et al., 1994). In addition, management practices such planting date, N fertilizer rate, hybrid maturity selection and harvest timing can affect grain moisture and test weight (Olson and Sander, 1988).

Fall weather conditions sometimes do not favor grain drying. Often corn producers cannot immediately harvest corn and large areas are sometimes left standing unharvested over winter. Producers wonder about the economic "trade-offs" of harvesting corn in spring, even though snow may melt and fields freeze enough to allow equipment traffic earlier during winter and late fall. The objective of this study was to determine the drying rate and test weight changes of late-developing corn standing over winter, with emphasis on hybrid and planting date influences.

MATERIALS AND METHODS

The study was conducted between 1992 and 1994 at the University of Wisconsin Agricultural Research Station located near Arlington, WI. The soil, a Plano silt loam (fine-silty, mixed, mesic; Typic Argiudoll), was fertilized for a yield goal of 150 bushels per acre. Plot management was similar to production practices of producers in the area. The experimental design was a randomized complete block in a split-split-plot arrangement with three replications. Main plots were seven planting dates: 21 April, 1 May, 10 May, 20 May, 1 June, 10 June, and 22 June. Split-plots were three corn hybrids: Pioneer 3417 (108 d RM), Pioneer 3578 (104 d RM), and Pioneer 3751 (97 d RM). On the planting dates of 10 and 22 June, Pioneer 3417 was switched to Pioneer 3921 (86 d RM), and Pioneer 3578 was switched to Northrup King PX9060 (80 d RM). Split-split-plots were measurements over time where ears were harvested mid-month in December, January, February, March and April. Plots in the study area were combine harvested during early November. On subsequent harvest dates, five ears were harvested from remnant field-standing plants.

Economic models were developed for three typical corn production situations involving livestock farming, on-farm drying and storage, and commercial elevator drying and storage. Grower returns were calculated using corn cash prices of $2.00 and $3.00 per bushel. Production costs and adjustments to grower return are described in Table 1. The yield loss rate of standing corn between December and April was assumed to be at 1% per week or 20% for the 20 week study period (Aldrich et al., 1986; Olson and Sander, 1988.).

Table 1. Production costs used to adjust grower return for three corn production systems.
Factor	Rate	Livestock	On-Farm	Elevator
		dollars
Handling costs	Bu	0.17	0.017	0.017
Hauling costs	Bu	0.04	0.04	0.04
Drying	Point bu	0.00	0.015	0.03
Storage	Bu month	0.00	0.02	0.04
Trucking	Bu	0.00	0.112	0.112
Test weight (discount < 54)	Lb/bu	0.00	0.005	0.005

Which Hybrids and Planting Dates Resulted in Immature Corn (>35% Moisture) at Harvest in November?

Immature corn was observed for the 108 and 104 day hybrids planted on 1 June, and for the 97, 86 and 80 day hybrids planted on 22 June (Table 2).

Table 2. Grain moisture in November for corn hybrids planted on different dates.
Planting	Hybrid relative maturity (days)
Date	108	104	97	86	80
	percent moisture
21 April	27	26	22	--	--
1 May	27	27	22	--	--
10 May	34	29	23	--	--
1 June	42	34	26	--	--
10 June	--	--	31	26	21
22 June	--	--	54	39	35
LSD(0.05)	1	2	3	2	3

Grain moisture of every hybrid increased with later planting date. Grain moisture increased from an average of 25 percent on 1 May to 34 percent on 1 June. Grain moisture further increased to an average of 43 percent on 22 June.

Earlier planting resulted in less grain moisture difference between hybrids in November. For example, the grain moisture difference between 108 and 97 day corn hybrids planted on 21 April was 5 percent. When the same hybrids were planted 1 June, the grain moisture difference was 16 percent.

Immature corn was observed for the 108 and 104 day hybrids planted on 1 June, and for the 97, 86 and 80 day hybrids planted on 22 June.

How Long Does it Take for Immature Corn to Dry to 20 to 25% Moisture?

Drying progressed at a rapid rate between November and December harvests, particularly for grain in the earliest four planting dates (Table 3). Grain moisture was still excessive in November for the three later planting dates.

Table 3. Corn grain moisture response of hybrids to harvest date for two planting dates.
	1 June			22 June
Harvest	P3417	P3578	P3751	P3751	P3921	N9060
date	Percent moisture
Nov	42	34	26	54	39	35
Dec	27	28	23	37	27	26
Jan	26	23	21	32	23	22
Feb	23	21	19	23	22	21
Mar	19	18	18	19	18	18
Apr	15	15	15	17	15	15
LSD(0.05)	3	4	4	4	4	5

Hybrid differences were observed at every harvest, except April. The largest moisture loss period was between November and December harvest dates when grain moisture changed from an average of 38 to 28 percent. For each planting date, longer season hybrids had greater moisture loss between November and December harvests than shorter season hybrids.

After December, grain moisture continued to decrease at the rate of 2 to 4 percent moisture each month. By April there were no differences among hybrids and planting dates, and grain had dried to below 20% for all treatments.

What Happens to Corn Test Weight During Late Fall, Winter and Early Spring?

Test weight for all hybrids and planting dates remained relatively constant between November and December harvest dates (Table 4). Between December and February harvest dates test weight declined and then increased slightly with March and April harvest dates. Every hybrid had its greatest test weight on the April harvest date. Since test weight was measured after oven-drying, we did not expect values to change once black layer formation occurred. Reasons for the slight response in test weight are not clear, but these results indicate that producers should not expect significant test weight improvements when delaying harvest from autumn to spring.

Table 4. Corn test weight response to hybrid and harvest date.
Harvest	Hybrid relative maturity
Date	108	104	97	86	80
	Pounds per bushel
Nov	53	53	52	50	50
Dec	53	52	51	51	49
Jan	52	52	51	50	49
Feb	54	53	52	48	49
Mar	54	54	52	51	51
Apr	56	56	52	51	51
LSD(0.05)	2

Test weight differences were observed between hybrids. For the 108 and 104 day hybrids test weight decreased when planted after 10 May, the 97 day hybrid test weight decreased after 20 May, and the 86 and 80 day hybrids were affected when planted after 10 June.

What Are the Economic Tradeoffs of Harvesting Wet Corn in November Versus Field Dried Standing Corn in April?

Fig. 1 shows the relationship between grower return and harvest for a 97-day hybrid. Three corn production situations are described for two corn cash prices and three planting dates (Table 1). The 97 day hybrid planted on 1 June returned as much in a livestock situation as on-farm and elevator storage and drying situations planted on 1 May (Fig. 1a). Planting date differences between the three corn production situations ranged from $240 to $260 per acre in November versus $200 to $220 per acre in April.

For early planting dates or $3.00 corn cash price, grower return decreased as harvest was delayed (Fig. 1b). For later planting dates or $2.00 cash price, grower returned remained the same or increased slightly with later harvest, even though grain yield was decreasing at one percent per week.

The largest difference between the three corn production situations was observed in November (Fig. 1c). Usually the livestock situation returned the most to the producer, while on-farm drying and storage was intermediate to elevator drying and storage. As harvests occurred further along into the winter, grower return differences became smaller between production situations. The difference between production situations in November was $120 per acre regardless of the cash corn price. By April, the grower return differences had narrowed to $20 per acre.

When corn is immature or late planted, it is best to harvest immediately in a livestock feeding situation. Under drying and storage situations, grower return of immature corn increases by letting it dry standing in the field, even under 20 percent yield loss.

Summary

These results document grain drying rates over winter and early spring for corn in two diverse production seasons. When averaged across seasons, drying rates varied depending upon hybrid and planting date induced differences in initial grain moisture percentage. When corn is immature or late planted, it is best to harvest immediately in a livestock feeding situation. Under drying and storage situations, grower return of immature corn increases by letting it dry standing in the field.

Producers also need to consider other "hidden" costs associated with leaving corn stand in the field:

Potential for mycotoxin development in the field versus in the bin.
Effect on ear drop when exposed to insect damage such as European Corn Borer.
Spring workload - Delayed planting the following spring will cause a yield penalty.
Soil compaction - More in the fall versus spring?
What will the actual yield loss be? How well will the corn stand?
Wildlife damage
Current feed supplies
Should we harvest as we feed (don't need to dry)?
Combine and heat damage effects when shelling and drying over 30% moisture corn.
Dry matter respiration losses

References

Aldrich, S.R., W.O. Scott, and R.G. Hoeft. 1986. Modern corn production. A&L Publications, Champaign, IL.

Dodds, M.E., and W.L. Pelton. 1967. Effect of weather factors on the kernel moisture of a standing crop of wheat. Agron. J. 59:181-184.

Olson, R.A., and D.H. Sander. 1988. Corn Production. In G.F. Sprague and J.W. Dudley (ed.) Corn and Corn improvement 3rd ed. Agronomy 18:639-686.

Sweeny, P.M., S.K. St. Martin, and C.P. Clucas. 1994. Indirect selection to reduce grain moisture in maize hybrids. Crop Sci. 34:391-396.