NC State Extension Publications

Hybrid Selection

Hybrid selection is a critical component of any profitable corn production system. Skillful hybrid selection requires that growers:

  • Understand the field environment.
  • Know how a corn plant grows and develops.
  • Collect and properly evaluate information describing the characteristics of hybrids available in their area.

Understanding Corn Hybrids

Corn hybrids fall into three categories, single crosses, three-way crosses and double-crosses. Single crosses, derived from the crossing of unrelated inbred lines, are characterized by uniformity of plant height, ear height and yield. This uniformity improves machine harvesting and is most advantageous when growing conditions are favorable. The three-way cross is slightly less uniform than the single cross because it is created by hybridizing a single cross seed parent with an unrelated pollen parent inbred. The double-cross is developed from four unrelated inbreds. Accordingly, it is less uniform in plant height, ear height, silking date, etc. than the single or three-way cross. In stress situations, this lack of uniformity is an advantage and it is the reason why double- crosses yield more consistently than single- crosses in a wide range of environments. Performance of the best single and three-way crosses will generally exceed that of the best double-crosses.

Genetically-Engineering Hybrids

Genetic engineering is a powerful, new hybrid development tool that is complementing traditional plant breeding. Genetic engineering is currently being used to introduce traits that confer insect, herbicide, or disease resistance to existing hybrids. Therefore, the basic yield potential of the hybrid is unchanged. Low yielding varieties before genetic engineering will be low yielding after genetic engineering. Corn growers should not select a hybrid based solely on the fact that it is genetically engineered. Instead, selection of a genetically-engineered hybrid should depend on whether the resistant traits that hybrid has are needed in the corn cropping system.

Hybrid Characteristics

For most growers selecting corn hybrids, yield is the primary consideration. However, successful corn producers choose hybrids on the basis of agronomic characteristics that complement their specific farm environment. For example, medium maturity, standability, seedling vigor and leaf disease tolerance are critical on farms comprised of organic soils. Early to medium maturity, standability, grain quality and drought tolerance are desirable hybrid characteristics for coastal plain peanut and tobacco growers. Livestock producers value good grain quality, while many piedmont and mountain bottomland silage growers demand gray leaf spot and viral disease tolerance. Most corn seed companies now routinely distribute information that allows growers to carefully scrutinize the relative agronomic attributes of hybrids they sell.

Hybrid Maturity

Corn producers should plant several hybrids differing in maturity. A 300-acre corn producer, for example, should plant a minimum of three hybrids. Planting hybrids that differ in maturity increases the odds that corn will be combined at optimum grain moisture levels throughout the harvest season and minimizes risk caused by the adverse effects of short-term water deficits and high temperatures. In North Carolina, the highest corn yields are produced by medium-season hybrids with a relative maturity of 110 to 118 days. Corn farmers with highly productive soils with good water-holding capacities should choose hybrids in the 112 to 120 day maturity range, while corn farmers with droughty soils should choose hybrids in the 108 to 115 day maturity range.

Maturity Rating Systems. Since it is important that growers know the maturity of hybrids they plant, several systems have been used to describe the "relative maturity" (RM) of corn. The "Minnesota System" is widely used by most seed companies to describe corn RM. Table 2-1 shows the RM of several corn hybrids commonly grown in North Carolina. Unfortunately, the actual days to maturity of corn hybrids will change based on when the hybrid is planted and the seasonal weather.

Table 2-1. Relative maturity, GDD requirements, and other plant characteristics for several popular hybrids grown in North Carolina.
Hybrid RM GDD Silking GDD Black Layer Planting Rate Emergence Stalk Strength Drought Tolerance Stay-Green
AgraTech ATX 700 111 1400 2615 26-30,000 Very Good Very Good N/A Good
AgraTech ATX 725 113 1450 2765 26-30,000 Average Very Good N/A Good
AgraTech ATX 787 116 1480 2810 26-30,000 Average Average N/A Average
Agripro HY9646 114 1450 2770 25-30,000 Average Average Good Good
Agripro AP9707 118 1470 2910 22-27,000 Good Good Very Good Good
Agripro HS9843 118 1465 2900 22-27,000 Good Good Good Good
Agripro HY9919V 119 1480 2940 22,27,000 Good Good Very Good Good
Agripro HS9977 124 1530 2980 20-25,000 Good Average Good Average
Augusta A285 108 1360 2575 22-27,000 Very Good Average Good Good
Augusta A385 113 1420 2730 22-27,000 Very Good Average Good Good
Asgrow RX 770 (1) 109 1380 2600 22-27,000 Good Average Very Good Average
Asgrow RX 826 112 1440 2650 22-27,000 Average Average Good Average
Asgrow RX 897 115 1480 2800 25-30,000 Average Good Good Average
Campbell's X7250 113 1425 2780 22-27,000 Average Good N/A Average
Campbell's X8020 116 1440 2860 24-28,000 Average Average N/A Average
Cargill 6888 109 1360 2590 22-27,000 Average Very Good Very Good Good
Cargill 7770 112 1410 2620 22-27,000 Excellent Very Good Very Good Good
DeKalb DK 546 104 1330 2620 25-30,000 Excellent Excellent Very Good Excellent
DeKalb DK 580 (1) 107 1350 2620 25-30,000 Excellent Good Very Good Very Good
DeKalb DK 585 108 1360 2630 25-30,000 Excellent Good Very Good Very Good
DeKalb DK 595 (1) 109 1355 2720 25-30,000 Excellent Very Good Very Good Good
DeKalb DK 621 112 1370 2770 25-30,000 Very Good Very Good Excellent Very Good
DeKalb DK 626 112 1420 2800 22-25,000 Very Good Good Very Good Excellent
DeKalb DK 632 113 1430 2820 24-28,000 Very Good Very Good Very Good Good
DeKalb DK 642 (1) 114 1445 2845 25-30,000 Good Average Average Very Good
DeKalb DK 658 115 1400 2800 25-30,000 Excellent Good Excellent Excellent
DeKalb DK 679 117 1455 2885 25-30,000 Excellent Average Very Good Very Good
DeKalb DK 683 118 1460 2930 25-30,000 Very Good Excellent Excellent Very Good
DeKalb DK 687 118 1455 2930 25-30,000 Good Excellent Very Good Very Good
DeKalb DK 714 121 1430 2950 27-30,000 Excellent Good Very Good Very Good
Mycogen 2888 111 1360 2760 25-30,000 Very Good Good N/A Average
Mycogen 7250 114 1400 2780 25-30,000 Average Good N/A Average
Mycogen 7885 115 1410 2820 25-30,000 Average Good N/A Average
Mycogen 8460 118 1470 2940 25-30,000 Average Good N/A Average
Novartis N4640Bt 102 1305 2530 26-28,000 Excellent Excellent Excellent Average
Novartis Max21 106 1375 2660 24-26,000 Average Excellent Average Average
Novartis N6800BT 110 1370 2710 26-30,000 Excellent Excellent Excellent Excellent
Novartis N63-G7 110 1360 2700 22-24,000 Excellent Very Good Excellent Excellent
Novartis N73-Q3 112 1420 2780 26-28,000 Excellent Very Good Very Good Very Good
Novartis N7590BT 113 1400 2810 26-30,000 Very Good Good Very Good Very Good
Novartis N7639Bt 113 1400 2800 24-26,000 Very Good Excellent Average Excellent
Novartis N75-T2 113 1415 2810 24-28,000 Very Good Very Good Excellent Good
Novartis N7931 115 1400 2820 25-28,000 Excellent Very Good Good Average
Novartis N79-L3 116 1400 2830 26-28,000 Excellent Very Good Excellent Excellent
Novartis N79-P4 116 1400 2830 24-26,000 Excellent Very Good Excellent Excellent
Novartis N83-N5 117 1450 2880 22-24,000 Very Good Average Very Good Average
Novartis N83-R7 118 1460 2880 24-26,000 Very Good Average Average Excellent
Novartis N8811 122 1510 2910 24-28,000 Good Very Good Average Excellent
McNair 508 138 1720 3180 28-30,000 Average Average Excellent Excellent
Pioneer 3140 118 1480 2790 24-26,000 Average Very Good Good Very Good
Pioneer 3163 119 1450 2840 24-26,000 Good Average Good Very Good
Pioneer 3167 124 1500 2970 24-26,000 Average Good Very Good Very Good
Pioneer 31B13 119 1500 2810 28-30,000 Average Average Very Good Very Good
Pioneer 31G20 119 1450 2840 26-28,000 Very Good Very Good Good Good
Pioneer 3223 116 1460 2790 28-30,000 Average Average Very Good Good
Pioneer 3245 115 1420 2760 26-28,000 Average Average Average Average
Pioneer 32K61 114 1450 2760 28-30,000 Average Very Good Good Very Good
Pioneer 3310 113 1410 2760 28-30,000 Average Very Good Good Very Good
Pioneer 3394 110 1380 2660 28-30,000 Very Good Good Good Average
Pioneer 3395IR 110 1380 2710 22-24,000 Very Good Very Good Average Very Good
Pioneer 33G26 112 1410 2740 28-30,000 Very Good Excellent Good Average
Pioneer 33V08 111 1380 2660 28-30,000 Very Good Very Good Good Very Good
Pioneer 33Y09 113 1410 2740 28-30,000 Very Good Excellent Good Very Good
Pioneer 34A55 110 1370 2660 28-30,000 Good Good Good Good
Pioneer 34T14 110 1360 2660 22-24,000 Good Very Good Very Good Very Good
S. States SS 598 108 1310 2600 25-28,000 Very Good Good Average Average
S. States SS 627 111 1370 2670 25-28,000 Very Good Good Average Average
S. States SS 682 113 1390 2720 24-26,000 Average Good Very Good Good
S. States SS 727 115 1400 2750 24-26,000 Good Very Good Very Good Very Good
S. States SS 742A 117 1420 2780 24-26,000 Very Good Excellent Very Good Very Good
S. States SS 747 116 1410 2780 24-26,000 Good Very Good Good Average
S. States SS 767 117 1400 2750 24-26,000 Average Very Good Good Average
S. States SS 827 119 1420 2810 25-28,000 Very Good Very Good Good Very Good
S. States SS 897 121 1480 2890 25-28,000 Good Very Good Good Very Good
S. States SS 943 125 1510 2950 25-28,000 Average Average Average Good
Genetically engineered hybrids based on this base hybrid are available with several different traits, i.e. RR, IMI, LIBERTY LINK, BT, etc.

Growing Degree Days. The most precise way to determine if hybrids actually differ in days to tasseling and silking or days to physiological maturity is to examine growing degree day (GDD) data supplied in the sales brochures of seed companies (Table 2-1). Growing degree days are calculated every 24 hours using the formula, GDD = [(Tmax + Tmin) / 2] - 50 where Tmax equals maximum temperature during the day and Tmin is the minimum temperature encountered during the day. Fifty degrees is substituted for the minimum temperature when temperature falls below 50 degrees. Eighty-six degrees is substituted for the maximum if maximum temperatures exceed 86 degrees. Those numbers are substituted in the calculation because corn grows very little below 50 degrees and growth slows markedly above 86 degrees. Tables 2-2 and 2-3 show the number of GDDs commonly recorded in central North Carolina. However, the actual number of GDDs experienced for any given period will vary from year to year due to changes in temperature. If a grower wants to select hybrids that minimize the crop's susceptibility to drought, hybrids should be chosen that, on average, will accumulate enough GDDs to start silking before June 20. Growers should also choose hybrids that vary by at least 100 GDDs in days to mid-silk. Growers can spread harvest by selecting a group of "companion " hybrids with a range of 300 to 400 GDDs to physiological maturity.

Table 2-2. Average monthly temperatures and daily GDD for Raleigh, NC.
Month Daily Maximum Daily Minimum Daily Average Temperature Daily GDD*
March 63 38 56 6
April 74 48 62 12
May 81 58 70 20
June 86 64 75 25
July 88 67 76 26
August 88 67 76 26
September 83 60 72 22
* Base temperatures of 50 and 86°F.

Table 2-3. Average accumulative, weekly, and daily growing degree days for Raleigh, NC (long-term averages).
Week Ending Accumulative GDD Weekly GDD Daily GDD
8 39 39 6
15 82 43 6
22 118 36 5
29 174 56 8
5 240 66 9
12 311 71 10
19 389 78 11
26 497 108 15
3 604 107 15
10 718 114 16
17 839 121 17
24 976 137 20
31 1113 137 20
7 1255 142 20
14 1420 165 24
21 1579 159 23
28 1757 178 25
5 1969 179 25
12 2118 177 25
19 2298 185 26
26 2489 191 27
2 2678 189 27
9 2863 185 26
16 3046 183 26
23 3227 181 26
30 3399 172 25
6 3572 173 25
13 3725 153 22
20 3868 143 20
27 3997 129 18
4 4114 117 17
11 4217 103 15
18 4314 97 14
25 4395 81 12

Corn Hybrids for Silage

High quality corn silage consists of a grain component that supplies 80% of the energy and 90% of the protein on a per-pound basis, and a stover component that supplies fiber and important amino acids such a carotene. The ideal corn hybrid for silage combines maximum grain production with a highly digestible, high-tonnage stover. A good hybrid for corn silage has the following characteristics: medium to tall stature, excellent grain yield, superior brittle stalk resistance, and excellent standability. Growers who use corn for silage should select hybrids with medium to late maturity. These hybrids tend to grow longer and have more tonnage. While tropical hybrids which have the capability for prolific growth may appear to be ideally suited for silage, keep in mind that much of the forage quality (energy and protein) come from the grain component. Most seed companies select materials that combine good grain yield with maximum tonnage. The North Carolina Official Variety Testing program measures silage yield performance and these results are available from your county Cooperative Extension office.

The Hybrid Selection Process

Corn growers are confronted with the difficult task of selecting three to four hybrids from approximately 100 varieties offered by more than 20 companies. Significant effort is required to sort through the confusing array of numbers and yield. To simplify hybrid selection, the process may be divided into eight steps that generate intelligent hybrid selections and increased corn profits.

Step 1) Analyze the role of corn on the farm. Pinpoint special corn hybrid traits needed in an operation. Are fields plagued with viral diseases or gray leaf spot? Do billbug problems and no-till demand that hybrids grow off quickly? Does the presence of swine or poultry make long-term storage and grain quality a priority? Priorities should be written down!

Step 2) Ask for product information describing the agronomic traits (yield, standability, maturity, disease ratings, grain quality, seedling vigor, etc.) of hybrids grown in local tests (see Table 2-1 above). Attend meetings where seed suppliers describe the strengths and weaknesses of their products. Notes should be taken at those meetings. Special attention should be paid to the hybrid characteristics that were listed as priorities in Step 1.

Step 3) Obtain hybrid data from independent sources. Call your Cooperative Extension agent and ask for NC State University's statewide corn variety testing results. Those data are found at the Official Variety Testing portal. Growers should also ask for the results of any county tests involving hybrid comparisons, as well as, a summary of state and local yield contests and make a list of those hybrids that consistently rank among the best performers.

Step 4) Discuss corn hybrid performance with seed dealers, grain buyers and fellow farmers. Everyone has strong opinions about corn hybrids. As they encounter tales of super hybrid performance and failure, growers should not give great credence to individual comments. However, when several experienced corn people observe that, "Every stalk was standing!" or "It grew off extremely fast!", astute growers can gain much insight into hybrid performance.

Step 5) Make a list of hybrids that appear repeatedly at the top of yield comparisons and yield contest summaries. Growers should strive to identify hybrids that perform well under diverse management regimes on numerous farms. Good hybrids will not always win yield contests and comparisons but they will appear among the leading entries. Hybrid performance may vary with seasonal conditions and soil types. Growers should be wary of newly introduced hybrids that may perform atypically in their first year of availability.

Step 6) Eliminate from the list those hybrids that do not meet the special requirements of your operation. Remember the special farm needs written down in Step 1! Corn producers should use notes taken at company-sponsored meetings, any hybrid literature obtained (Step 2) and information gathered locally (Step 4) to cull hybrids from the list that are not suited to their style of corn farming.

Step 7) Choose from the hybrids remaining on your "short list". Corn producers should review their information and notes to ensure that they have selected hybrid maturities that adequately spread their harvest (Table 2-1). If there are two promising hybrids of equal yield potential, their performance can be compared with a formula traditionally used by plant breeders. The formula,
Yield + [% standing plants - (5 x % grain moisture)]
can identify hybrids with the most profit potential because it emphasizes standability and low grain moisture as well as yield.

Step 8) Conduct your own hybrid comparisons. Each year, corn producers should select 4 to 6 promising hybrids and evaluate them on their farm with their management practices. The best procedure for grower testing of hybrids is the strip test where each hybrid tested is grown adjacent to a common "tester" hybrid. The strip test, with tester hybrids, permits any yield data collected to be adjusted for soil variability. If not using a tester, growers should place the hybrids they are considering beside the hybrid that has performed best for them in the past. Growers conducting their own hybrid evaluations must remember to select uniformtest fields with minimal soil variability and restrict comparisons to hybrids of the same maturity. On-farm hybrid evaluations are simple for growers who use combine-mounted GPS receivers and yield monitors to create GIS yield maps. Corn producers with yield monitors willfind it easy to compare several hybrids at multiple farm sites.

High Oil Corn Production

High oil corn is a special type of corn that has higher percent oil content than regular #2 yellow corn. Typically #2 yellow corn has from 3.5 to 4.0% oil. Ideally, high oil corn should contain 7.0 to 8.0% oil. In samples tested in 1996-1998, the oil content of high oil corn hybrids ranged from 4.6 to 8.1% compared to normal dent corn that had oil contents ranging from 2.7 to 4.0%. In addition to the higher oil content, high oil corn kernels usually have a slightly higher percent protein and, even more importantly, higher amounts of amino acids such as lysine, threonine, and tryptophan that are important in the diets of poultry and swine.

The primary advantage of high oil corn is to the livestock producer, particularly poultry, dairy, and swine producers. For livestock producers who are not using added fat, high oil corn increases daily weight gains by as much as 10%. As a result, feeders do not have to pay for expensive fat or amino acid additives. They save money and maintain or increase the productivity of their operation. For corn farmers the benefits comes from having satisfied customers who are willing to share some of the increased profits with them in the form of premiums paid for high oil corn. Currently, livestock feeders are paying form $0.15 to $0.30 more for high oil corn.

The disadvantages of high oil corn come from the potential for lower corn yields, increased kernel damage, and the potential for increases in insect damage. Because almost 10% of the seed in the bag is the unproductive male pollinator, yield decreases of up to 10% are possible. Furthermore, in a year when drought stress occurs during pollination, the smaller amount of pollen available and the mismatch in the timing of silk emergence and pollen shed could reduce yields even more. Companies producing high oil hybrids recommend increasing seeding rates to obtain higher plant populations that make up for the loss of productive plants. This may not be feasible on droughty soils. The Dupont pollinators are designed to compensate for drought conditions by shedding pollen over a longer period (2 weeks vs 7-10 days), and by producing more pollen. Table 2-4 shows the yield and oil content of a number of high oil hyrids and compares them with three conventional hybrids.

Table 2-4. Oil content, test weight, and yield of three conventional hybrids compared with several high oil corn hybrids. Data represent the average of two sites in Beaufort County in 1998.
Hybrid Oil Content (%) Test Weight (lbs/bu) Yield (bu/acre)
Pioneer 3245* 3.7 58.0 166.8
DeKalb DK 595* 3.5 54.0 165.0
Pioneer 3394* 3.7 54.5 162.8
Novartis N7577TC 7.1 53.3 158.2
Pioneer 32R90TC 6.9 56.8 157.2
Asgrow RX 770TC 7.3 52.5 137.3
Wyffel X6868TC 8.6 52.8 136.2
S. States SS 767TC 7.3 50.3 135.2
Novartis N6423TC 6.1 52.8 134.9
DeKalb DK 595TC 6.3 54.1 134.7
Cargill 6690TC 7.5 54.8 133.6
Novartis N6611TC 8.0 54.0 133.1
Cargill 7790TC 6.7 53.5 132.6
Wyffel W7029TC 6.9 52.8 129.0
Cargill 6390TC 6.5 52.5 127.0
Wyffel W7978TC 6.5 49.5 124.8
Wyffel X6588TC 7.3 53.5 120.1
S. States SS 727TC 6.9 51.0 116.8
AgraTech ATX 700TC 7.0 50.5 113.3
AgraTech ATX 685TC 6.1 52.5 105.6

The increase in embryo vs the hard endosperm results in a softer kernel that is more prone to damage. Trials have shown a significant increase in kernel damage in the midwest. Softer kernels and high oil also makes this corn attractive to insect feeding. Currently, there are no high oil Bt hybrids, but this is being considered.

If corn yields from a high oil hybrid and a conventional hybrid remained the same there would be no need for premiums. The increase in demand for high oil corn and the increased income available to purchase high oil corn would result in market price increases for these hybrids. Therefore, the open market system would provide the incentive for growers to select high oil hybrids. Unfortunately, the reduced yield potential from high oil hybrids make premiums necessary. For instance, consider the following scenario: a producer plants a high oil corn hybrid and a conventional hybrid side by side. At harvest, the conventional hybrid yields 100 bu per acre verses the high oil hybrid that yields only 90 bu per acre (10% yield reduction due to the unproductive male pollinator). At the current market price of $2.50 per bushel the conventional field returns $250 per acre. The high oil corn returns $225 per acre. In order to make up for the decrease in income from the high oil hybrid the producer would have to be paid a premium of $0.28 per bushel. The reduction in yield potential that exists in the current high oil corns are the reason premiums are necessary in the marketplace. A corn producer who is interested in the high oil corn market must determine the potential yield reductions before agreeing to a premium contract. Otherwise, he/she will not be able to calculate the return from high oil corn.

Despite the potential for yield reductions, the future for high oil corn in North Carolina is very bright. Because livestock feeders make up a large portion of our corn market, there will be an increasing demand for value added corn products. Livestock feeders don't want to have two separate facilities, one for high oil corn and one for #2 yellow corn. Therefore, because high oil corn has such important feeding benefits, they will be moving to make high oil corn the only product they buy. North Carolina corn producers are in a unique position because our corn is usually harvested in August at a time when corn stocks are low. Livestock feeders interested in maintaining their supply of high oil corn should be willing to pay better premiums for this early crop in order to make sure that they do not have to convert back to feeding normal #2 yellow dent corn.

This is only the beginning of the trend toward value added products. High lysine corn, low phytic acid corn (results in better phosphorus utilization by livestock), low linolenic oil soybeans and other value added crops will be coming in the near future. Growers will be moving toward contract marketing with livestock producers to provide these new value added crops.

Corn Seed

Recent improvements in planter technology have produced planting units that use vacuum or air pressure to hold the seed to a plate or drum until it reaches the release point. Usually, these types of planting units can use different seed sizes and shapes depending on the size of the hole in the plate or drum. However, experience has shown that round kernels tend to work best because they flow better in the units and fit the plate or drum better. Finger pickup units can also plant a wide range of kernel shapes and sizes. Again, farmer experience has shown that small to medium kernels with a round shape work best. The key to accurate planting is to fit kernel shape and size to the planter plate, drum, or finger pickup unit that you are using. Corn producers should carefully select kernel size and shape based on their equipment.

Kernel Size Effects on Yield and Emergence

It may be argued that large kernels possess greater carbohydrate reserves that enable them to germinate more consistently and uniformly than small kernels in cold, wet or compacted soils. In contrast, smaller seed sizes require less moisture for germination; they may emerge more reliably in dry planting seasons. However, research has not found any relationship between kernel size or shape and emergence or yield. This observation suggests that growers with placeless or vacuum planters should take advantage of lower prices asked for less popular seed sizes and shapes. It also suggests that, in years of limited seed availability, growers should purchase corn hybrids on the basis of their agronomic performance, not their kernel size.

Germination and Stand Establishment

To determine the number of live plants expected from a given seeding rate, growers should use the following equation:

Expected emergence = Seeding Rate X (%Pure Seed/100) X (%Germination/100)

Under field conditions it is not uncommon to find that as many as 15% of the seeds planted do not produce a live plant.

Planting Dates for Corn in North Carolina

Maximum corn yields are obtained from a plant that grows for the longest period of time in the absence of heat or moisture stress. This means that the selection of planting date at a given location is based upon the desire to obtain the longest growing period while at the same time avoiding periods of drought or high temperatures. While this sounds simple in principle, it is difficult to accomplish in practice. Across North Carolina the period of least rainfall and maximum evapotranspiration occurs from July 10 to August 1 (Figure 2-1). This period also experiences some of the highest temperatures particularly night temperatures. In addition to these factors, effective rooting depths in most soils in North Carolina are restricted to the upper 8 to 24 inches of the soil profile by acidic subsoils, compacted layers, and other root restrictions. The combination of low rainfall, high temperature, high water demand, and shallow rooting depths almost guarantees that the corn crop will experience moisture or temperature stress during the summer months.

In any given year, it is impossible to accurately predict when moisture or temperature stress will occur. Long-term data suggests that dry periods with high temperatures occur most often during the period from June 20 to July 15. Therefore, the best strategy that a corn grower can follow in selecting a planting date is one that seeks to avoid pollination during this risky period. Depending on the maturity of the hybrid, field data indicate that corn should be planted either early in the growing season or late enough so that only the early growth occurs during July. Unfortunately, planting corn later in the growing season increases insect and disease pressure and late harvest misses the opportunity of higher corn prices that occur early in the fall. This means that the early planted corn has the best chance of producing high yields and higher profits. With this in mind, recommended planting dates are based on getting corn planted as soon as possible in the spring.

Corn should be planted when soil temperatures reach 55°F at a 2 inch depth and the weather forecast shows a good chance of warm temperatures over the next few days. Figure 2-2 shows the dates when soil temperatures generally reach 55°F. In the tidewater region on organic soils this usually occurs before March 20. In the coastal plain 55°F soil temperatures occur from March 20 to March 25, in the piedmont from March 25 to April 5, and in the mountains from April 5 to April 20. Since soil temperatures are effected by the amount of soil residue and moisture, planting dates for no-till systems will be later than those used for conventional tillage. When using no-till practices, planting dates can be delayed by 3-5 days.

Planting date studies conducted at NCSU have demonstrated that corn yields decrease with late planting. In the coastal plain and piedmont areas, corn yields decrease, on average, one bushel per acre for every day that planting is postponed after April 15. In the tidewater and mountain regions of the state, corn yields start decreasing after May 1. The later dates in the mountains and tidewater regions are due to the capacity of the soils to hold greater amount of water that extends the period during which corn growth occurs without stress. The accepted cutoff date for corn planting in North Carolina is May 10. After this date, it is generally more profitable to plant another crop. The risk of low corn yields increases because pollination will most likely occur during a period of moisture stress.

One way to reduce the risks associated with planting corn late is to switch from full-season hybrids to medium- or early-season hybrids. Best results are found when growers are advised to switch from full-season to medium-season hybrids around April 28, and from medium-season to early-season hybrids around May 7.

There are some cases where growers should consider planting later in the growing season. Such as when tropical corn hybrids are grown for silage. Tropical hybrids experience rapid growth early during their growth cycle and have more prolific root systems than conventional corn hybrids. Therefore, to avoid lodging tropical hybrids must be planted late. The recommended planting dates for tropical hybrids are from June 1 to June 20. Another situation that is showing some promise in the mid-Atlantic region is the use of early maturing hybrids as a double crop following wheat. By using a Bt hybrid, the grower can avoid insect damage and by planting late the corn will be in the vegetative stage during July. Research in Virginia has found that corn yields range from 80 to 140 bushels per acre in this system. We recommend that growers use double cropped corn only on their better land.

Figure 2-1. 30-year averages for rainfall and potential evaporat

Figure 2-1. 30-year averages for rainfall and potential evaporation at Smithfield, NC.

Figure 2-2. Average date when soil temperature at 2" exceeds 55F

Figure 2-2. Average date when soil temperature at 2 inches exceeds 55 degrees F for most of the day.

Selecting Plant Population

Plant Population and Soil Moisture Holding Capacity

Plant population is a critical factor in corn production, especially when corn is grown on sandy soils in dry seasons. Plant populations should be selected according to the soil moisture-holding capacities of individual fields. Corn plant populations per acre should increase with increasing soil moisture holding capacity (Tables 2-5 and 2-6). On soils with good to excellent soil moisture holding capacity, growers should seek to obtain a maximum of 27,000 plants/acre. Seldom is there a need to seed dryland corn at final stands exceeding 28,000 plants/acre. On soils with average water holding capacity, they should plant to obtain a final stand between 22,000 and 24,000 plants/acre, and on soils with poor water holding capacity final stands should not exceed 19,000 plants/acre.

Table 2-5. Planting population guidelines for different soil types with dryland and irrigation corn.
Soil Type Texture Water-Holding Capacity (inches/inch) Kernel Drop* (x 1000) Final Stand (x 1000)
Dryland Corn
Wagram loamy sand 0.09 19,800 (10.6) 18,000
Norfolk sandy loam 0.11 22,000 (9.5) 20,000
Goldsboro sandy clay loam 0.13 24,200 (8.6) 22,000
Hyde shallow muck 0.20 30,000 (7.0) 27,000
Ponzer muck 0.22 30,000 (7.0) 27,000
Irrigated Corn (with hose-reel or cable-tow machines)
Wagram loamy sand 0.09 22,000 (9.5) 20,000
Norfolk sandy loam 0.11 24,200 (8.6) 22,000
Goldsboro sandy clay loam 0.13 26,400 (7.8) 24,000
Irrigated Corn (center pivot or linear move machines)
Wagram loamy sand 0.09 31,900 (6.5) 29,000
Norfolk sandy loam 0.11 31,900 (6.5) 29,000
Goldsboro sandy clay loam 0.13 31,900 (6.5) 29,000
* Based on 30-inch row spacing and 90% germination. Numbers in parentheses indicate number of inches between seeds.

Table 2-6. Recommended final plant populations for corn.
Location Hybrid Maturity
Early to Mid Late
Tidewater 27,000 25,000
Coastal Plain 24,000 22,500
Piedmont 22,000 20,000
Mountains 25,000 23,000

Plant Population and Crop Management

A grower should also select a plant population that complements his package of production practices. Seeding rates should be matched to tillage systems, capability of the hybrid to tolerate increasing plant populations, the standability of specific hybrids and intended use of the crop (for example, silage versus grain). Corn growers should be aware of the recommended plant populations for the hybrids they grow (see section on hybrid selection).

Plant Population, Irrigation and Sub-irrigation

Numerous irrigated corn studies have shown that 29,000 plants/acre is the optimum plant population for corn when soil moisture is not limiting. When supplemental moisture is available to corn via irrigation, seeding rates should increase proportionally to the quantities of water that can be supplied. In extremely hot, dry years, most growers using hose reel machines can not deliver the quantities of water needed by corn. Growers with sub-irrigation capabilities should use the same seeding rates as those used by growers irrigating with hose reel machines. In contrast, center pivot irrigators who water aggressively can plant to obtain a the ideal plant population of 29,000 plants/acre. Under center pivot irrigation, plant population should not change with soil type. However, it should be obvious that center pivot operators tending corn on sandy soils will have to irrigate more often.

Plant Population and Drought

Many growers producing corn on drought-prone soils strive for final stands of 16,000 to 19,000 plants/acre. Reduction of plant population to that level is worrisome if adverse seedbed conditions or insect problems are encountered. When corn stands fall below 14,000 plants/acre, satisfactory weed control is seldom attainable. However, the probability of drought is far greater than the probability of insect or seedbed problems. Growers using low plant populations as a hedge against drought should regularly scrutinize hybrid information to ensure that the hybrid they choose will still produce adequate yields at low plant densities when rainfall is ample. Those same hybrids should be among the highest yielding when soil moisture is lacking and yield levels are low.


Prolific hybrids are corn lines that bear more than one ear per plant. At normal seeding rates, the second ear on a prolific hybrid may not contribute significantly to final yield. At low plant populations, the contribution of a second ear to grain yield can be significant. Prolific corn hybrids use nitrogen efficiently and tolerate stress better than single-eared hybrids. However, it is important to recognize that, to date, commercial hybrids producing more than one ear per plant in low population scenarios have not out-performed single-eared hybrids that responded to low seeding rates by "flexing" their ear size to produce more grain.

Silage and No-Till Considerations

Silage producers generally should increase corn seeding rates by 2,000 to 4,000 plants/acre. The elevated plant population increases tonnage and total digestable nitrogen production without undue risk of lodging because silage harvest occurs as soon as plants are physiologically mature. Experienced no-till farmers with up-to-date planting equipment should not increase corn seeding rates. Before planting techniques were perfected, it was customary for no-till growers to compensate for inexperience and poorly performing planters by dropping up to 15% more kernels. Improvements in no-till equipment and increased residue management experience enables today's no-till corn producers to use standard seeding rate recommendations.

Planter Speed

Planter speed is critical in obtaining optimal seeding rates in conventional and no-till corn production systems. Most planter types function best at 4 1/2 miles per hour; successful no-till growers plant slower. Excessive planter speed will manifest itself in erratic stands, poor weed control and low yields. Corn growers must recognize that planter performance has the greatest influence on their ability to produce uniform stands of the desired density. The potential yield for a given field is highest when corn plants are evenly distributed. Row widths and seeding rates that combine to distribute plants uniformly across a field ensure that individual plants have maximum access to available light, nutrients and soil moisture. The ability of growers to select the proper plant population and to achieve that plant density with precision spacing and uniform emergence within rows determines, to a great degree, the profitability of corn enterprises.

Selecting Row Spacing for Corn Cropping Systems

The choice of row spacing is one of the most fundamental components of a corn cropping system. Narrow rows permit more uniform plant distribution and reduce the inter-plant competition for moisture, nutrients, and light. However, as row width decreases, the difficulty in managing weeds, insects, and fertility increases and there is an increase in machinery costs. In choosing row width, the corn grower must balance the potential increase in yield that comes from narrower rows against the additional machinery cost and management that a narrow row system demands.

Yield Response to Row Width

Tidewater Area:

Studies conducted in the tidewater area of North Carolina have consistently shown that corn yields increase as row spacings decrease (Figure 2-3). Corn yields increase by 8.5% as row width is decreased from 36 to 30 inches, and 6.0% as row width is decreased from 30 to 20 inches.

Coastal Plain:

In the coastal plain area corn yields were shown to increase by 11.5% as row width is decreased from 36 to 30 inches, and 3.5% as row width is decreased from 30 to 20 inches.

Piedmont Area:

Corn yields increase by 5.0% as row width is decreased from 36 to 30 inches, and 4.8% as row width is decreased from 30 to 20 inches in the piedmont.

Economics of Narrow Row Corn

The potential yield increase from changing from wide to narrow rows must be weighed against the cost of that change, both in terms of equipment modification and an increase in the annual input costs. Table 2-7 shows a comparison between potential yield increases and the returns to a narrow row corn system. Costs of converting equipment to narrow rows are considered (figured at $20,000) as well as the interest cost and the increase in fertilizer. Additional insecticide costs are not figured in this chart. Given an 8.5% yield increase between 36 and 30 inch rows, corn growers with over 250 acres of corn with a yield history of 125 bu/acre or higher can justify moving from 36 to 30 inch rows. Growers considering moving from 30 to 20 inch rows must grow over 350 acres of corn to justify the expense. Note that the difference in overall profit between wide and narrow rows is small. Even a grower with 500 acres of corn at a 6% yield increase will only make an additional $2,000 by converting to narrow rows.

Table 2-7. Economic return from changing to narrow rows at a range of yield increases.
Narrow-Row Increase Return Per Acre
% 125 150 175
250 Corn Acres
2 -$14 -$13 -$12
4 -$10 -$8 -$6
6 -$6 -$3 -$1
8 -$3 -$1 -$5
350 Corn Acres
2 -$8 -$7 -$6
4 -$5 -$3 -$1
6 -$1 -$2 -$5
8 -$3 -$7 -$11
500 Corn Acres
2 -$4 -$3 -$2
4 -$0 -$2 -$4
6 -$4 -$7 -$9
8 -$8 -$11 -$15
Costs Assumed:
Convert corn head $5000
Convert planter $6500
Convert Sprayer $ 500
Purchase new dual tires and rims $8000
Total machinery modification of $20,000 carried over 5 years at 10% interest - annual cost of $5000
Fertilizer costs for narrow rows increase at the same percentage as yield.
Cash price for corn - $2.40; Herbicide and seeding rates stay the same.

Narrow Row Corn Cropping Systems

It is clear that although there is a yield advantage to narrow rows in North Carolina, the profit margins are slim. However, if a grower can reduce the cost of the equipment conversion and maximize yield increases, he/she can increase long-term profit. To do this requires a consideration of the components needed to implement a profitable narrow row cropping system.

Crop Sequence

No data has been developed showing narrow row corn response to different cropping sequences. However, crop rotations that improve soil fertility and productivity of the system should have an advantage. Corn-soybean or corn-wheat-soybean sequences both should have positive benefits in narrow row systems.

Crop Management.It appears that hybrid selection, planting dates, or plant populations do not impact the yield increases found in narrow row systems. Therefore, the grower should not change current practices. Increasing plant populations is not required or recommended to obtain the desired yield increases from narrow row systems.

Soil Management

Anything that increases available soil moisture should improve the consistency of yield responses in narrow row systems. Therefore, no-till practices are recommended for narrow row corn. A key observation about narrow row spacings is that as row spacings decrease the amount of starter fertilizer or in-furrow insecticide within the immediate area of the seedling decreases. The root system of a small corn seedling only explores a limited area; therefore, there is less concentration of fertilizer or insecticide in the root zone. Studies have shown that per-acre rates of starter fertilizer need to be increased as row spacings narrow. Starter fertilizer rates should increase 1 to 1.5 pounds per acre for every inch that row spacing is decreased. Sidedress nitrogen should be applied earlier (14-21 days after emergence) to avoid problems with crop damage from the application operation.

Weed and Pest Management

Because higher per acre insecticide rates may be needed in narrow row corn systems and this may not be covered by current labeling, we recommend that growers use row spacings of 30 inches or greater where there are heavy infestations of billbugs, wireworms, or corn rootworms. Rotations that reduce these pests will be critical to maintain the productivity of a narrow row corn system. Herbicides should be selected that are highly effective against the weeds present with the idea that followup applications may not be possible. The residual activity of the herbicide will be less of a consideration in narrow row systems. Again, timing is critical. The application needs to be made in the 14-21 days following emergence before the crop canopy closes.

Equipment Management

Because of the low profit margins for converting to narrow rows, equipment conversions should be made to meet the needs of the grower, not with the goal of switching to narrow rows. If soybean planter can be used or if the grower is buying a new planter, then a consideration can be given to changing to narrow rows. Changing wheel spacings should be done to accommodate all crops that the producer raises. Corn row widths should be selected to match with the row spacing of the other crops. For instance, if the grower is raising cotton on 36 inch rows, then 18 or 24 inch corn rows will work. If planting soybeans on 15 inch rows, then 15 in corn rows should be selected. The goal is to make the conversion without incurring excess costs and with the idea to accommodate all crops so that wheel spacings can remain the same.


Narrow row corn systems show promise for increasing corn yields conservatively from 4 to 6%. For growers who raise over 350 acres of corn this would result in a small profit. A complete corn management system as outlined above should be used to maximize yield increases and minimize costs.

Figure 2-3. Corn yields at three different row widths in 1996 Ca

Figure 2-3. Corn yields at three different row widths in 1996 Camden County.

Seedbed Preparation and Planting Considerations

Seedbed Preparation

Improvements in planter design have reduced the emphasis on seedbed preparation for corn, but the basic fact still remains that uniform and consistent stands are the result of seed placed in an optimal environment for germination and emergence. The optimal environment for a corn seed has three requirements: adequate moisture, firm seed to soil contact, and temperatures above 55°F. The moisture content of the soil at the depth that the seed is placed should be from 2 to : of field capacity. This means that the soil should be moist enough to show visible signs of moisture, but not so wet that it can be molded into a ball without easily crumbling. In dry conditions, planting depths should be increased to insure adequate moisture at the seeding depth.

For germination to occur rapidly and uniformly across the field the seed must be surrounded by soil. The planter should be adjusted so that the seed is placed at the proper depth with good soil contact and cover. This is the key to success in no-till systems. No-till planters frequently use fluted coulters to cut a trench or slot into which the double-disk seed openers place the seed. If these coulters cut too deep or if the flute design allows too much soil to be disturbed they leave a deep ragged slot which allows the seed to fall deeper than intended. Good seed-soil contact is almost impossible in these situations. On the other hand, no-till planters working in heavy trash tend to ride up on the trash mat resulting in seed placement that is uneven and inconsistent. Planting into a conventionally tilled seedbed which is cloddy from being worked too wet or, in the case of heavy organic soils, which is too fluffy, will also result in poor seed-soil contact. Farmers using conventional tillage should avoid multiple tillage passes which lead to puddling and compaction of the soil surface. Modern planters have the capability to work in rough seedbeds and do not require excess tillage to be successful in placing the seed correctly.

Soil Temperature

Seed germination and seedling emergence are affected by many environmental conditions, particularly soil moisture and temperature. Wet soils or soils with heavy amounts of residue will be cooler than soils that have ideal moisture or no cover. On all but the heavy organic soils of eastern North Carolina, Atrash whippers@attached to a no-till planter have been shown to be effective in promoting better germination and emergence by reducing surface cover over the seed and by stirring the top 2@ of soil. For best results, corn growers should avoid planting into cold, wet soils if at all possible. Corn should be planted when soil temperatures reach 55°F at a 2 inch depth and the weather forecast is favorable. In tidewater, piedmont, coastal, and mountain areas of North Carolina, 55°F soil temperatures are usually reached just prior to March 20, March 25 to April 5, March 20 to March 25, and April 5 to April 20, respectively.

Planting Depth

Depth of planting will influence several factors associated with stand establishment and should vary with planting date. In general, the deeper the planting depth, the cooler the soil and the slower the emergence. Temperature in the first 2 inches will be greatly influenced by air temperature and can fluctuate as much as 10 to 15°F during a single day. Soil temperatures are fairly consistent at the 2 to 4 inch depth, and warm gradually as the season progresses. Normal planting depths range from 114 to 2 inches. Since cold temperatures can reduce germination, planting depth should be 12 to 1 inch shallower at very early planting dates.

Another impact of planting depth is associated with the process of germination and seedling growth. One of the first structures to emerge from the seed during the germination process is the coleoptile (co-lee-op-tile), a sheath like structure that protects the young shoot (Figure 2-4). Without the coleoptile, the tender shoot or plumule, would be shredded before it could penetrate the soil surface. Planting corn seeds too deep can result in the coleoptile growth terminating well below the soil surface. As the shoot grows through the coleoptile tip, it will continue to grow unprotected towards the surface. In heavy soils, crusted or compacted soils, an unprotected shoot will be torn apart before it can emerge.

Research has shown that planting too shallow or too deep can adversely affect corn yield. Planting depths greater than 2 inches result in seedlings with less vigor, slower growth and development, and less yield. Conversely, planting depths less than 0.5 inch lead to poor seminal root development, shallow rooting depth, and poor drought tolerance. Special care should be taken not to plant corn too shallow on landscapes prone wind erosion. Strong winds can uncover seed and destroy stands. It is, therefore, important to regularly check the seeding depth during the planting operation.

Figure 2-4. Seed germination process.

Figure 2-4. Seed germination process.

Harvest and Storage

Preharvest Losses

An efficient corn harvest is the result of attention to management throughout production and harvest seasons. Decisions, such as the selection of hybrids that mature at different times (see the section on hybrid selection), can help improve harvest conditions and insure that the corn produced makes to the bin. Other details, such as combine preparation and repair, require careful planning, but payoff in less down time and better combine performance. Estimates have put average corn harvest losses in North Carolina anywhere from 5 to 10 bushels per acre, with expert operators and managers reducing this to about 1 to 2 bushels per acre. The added income from an efficient harvest is almost pure profit, so a timely harvest and the few minutes spent on careful combine adjustment can be extremely profitable.

Harvesting early is the key to successful corn production. Those who harvest early can:

  1. Receive premiums for new-crop corn paid by livestock producers.
  2. Avoid adverse consequences of crop damage from a hurricane.
  3. Avoid field losses resulting from ear drop and fungal pathogens.

Delayed harvest leads to reductions in corn yields due to ear drop, stalk lodging and, to a lesser extent, from reductions in kernel weight. Fungal diseases that infect the corn kernel also become more and more of a problem as harvest is delayed. Mycotoxins, such as aflatoxin and fumonisin, which are produced by these fungal pathogens increase as harvest is delayed often resulting in corn that is unsuitable for human or livestock use. Ideally, corn harvest should begin as soon as the grain reaches moisture levels of 25% or less. Under favorable conditions following black layer formation, corn should be ready to harvest in 10 days or less.

Harvest Losses

Besides reducing pre-harvest losses, early harvest also results in less combine loss. There are several points where grain can be lost during combining. These losses can be divided into three categories:

  1. Ear losses are ears that are left on the stalks or dropped from the header after being snapped.
  2. Loose kernel losses are kernels that are left on the ground either by shelling at the snapping rolls or by being discharged from the rear of the combine.
  3. Cylinder losses are kernels left on the cob due to incomplete shelling.

Proper combine operation involves measuring harvest losses and then making adjustments in settings or harvest speed to correct them. Use the following procedures to measure harvest losses.

Determine ear loss. Pull the combine into the field and harvest at the usual rate for about 300 feet. Pace off an area behind the machine that contains 1100 of an acre (Table 2-8). Gather all unharvested ears from the area. Each3 pound ear represents a loss of one bushel per acre. If the ear loss is above one bushel per acre, you should check an adjacent area in the unharvested corn to determine if the ear loss occurred before the combine pulled into the field. If you determine that ear loss is occurring at the combine header, carefully examine the following: the speed of the gathering chains and rollers, ground speed, stripper plate settings, and worn or missing ear guards. Often combine ear loss is the result of excessive roller speeds which cause the ear to bounce out of the header. Experienced combine operators match header and combine speeds to prevent header losses.

Table 2-8. Row length in feet per 1100 acre.
Row Width (in) Four Rows Six Rows Eight Rows Twelve Rows
30 43.6 29.0 21.8 14.5
38 34.5 23.0 17.2 11.5
40 32.7 21.8 16.3 10.9

Next determine loose kernel losses. Back the combine up a short distance and examine the area between the standing corn and the spot where the rear of the combine was by counting the number of corn kernels in a square foot area. Do this at two or three spots and average your results. For every three kernels found in a square foot area, the combine is losing a bushel of corn per acre. Repeat this procedure in the area where the chaff from the combine has been discharged. Compare your results to determine where the loose kernel losses are occurring. Examine header speed, chaffer settings, air settings, and combine speed as possible causes of loose kernel losses.

Finally, determine cylinder losses. Examine corn cobs that have been discharged from the rear of the combine. The presence of kernels still attached to the cob is a sure sign of cylinder loss. This type of loss can be especially serious since a single cob can contain enough kernels to cause yield losses of up to 3 bushels per acre. Examine concave settings, cylinder speed, and ground speed to eliminate cylinder losses.

When properly adjusted and used, grain loss monitors can be beneficial in reducing harvest losses. Crop conditions can change drastically over the course of a few hours and grain loss monitors can assist the combine operator in making minor adjustments throughout the harvest season.

Drying Corn for Storage

Drying Costs.

One of the reasons often cited for not harvesting in a timely manner is the cost of drying corn to the proper moisture levels for storage. If the crop is to be stored for any given period and if fungal growth is to be stopped or reduced, corn moisture content should not exceed 15.5%. Because early harvest is done when grain moisture often exceeds 17%, drying is necessary. Grain drying costs can be estimated by the following equations:

Energy cost ($/dry bushel) = [(LP gas price X 0.02) + (Electricity price X 0.01)] X (initial moisture B 15.5)

Energy cost ($/wet bushel) = Energy cost per dry bushel X (100 B initial moisture)/84.5

These calculations are based on the fact that it takes 0.02 gal of LP gas and 0.01 KWH of electricity to remove 1% moisture per bushel. Figure 2-5 shows per-bushel drying costs when LP gas costs $0.60 per gallon and electricity $0.06 per KWH. Keep in mind these costs do not cover the cost of the drying equipment or the extra labor involved in operating a dryer but the extra costs of grain shrinkage (weight loss caused by removing moisture and handling) are shown. When one considers that drying corn at 25% moisture costs approximately $0.12 per day, it is clear that saving two to three bushels per acre by harvesting early can easily pay for drying costs. It should also be noted that there is a financial penalty for over-drying. If the crop is to be sold immediately, avoid drying corn below the base market level of 15.5%. However, if the corn is to be stored through the summer, extra drying to 13.5% is needed to prevent moisture accumulation in warm temperatures. The additional cost of drying corn to 13.5% should be considered as a cost associated with long-term storage.

Types of Drying Systems

In-bin drying systems consist of a perforated floor in the bottom of the bin that covers a chamber approximately 16 inches high. A large fan and propane heater is attached to the bin so that heated air is blown into this chamber at the bottom of the bin. The advantage of this system is that the bin can serve both to dry and store the grain. The disadvantage to this system is that as the depth of corn over the perforated floor increases, the resistance to air movement increases. This reduces the volume of grain that can be effectively dried. Corn grain depth for grain drying using an in-bin system should not exceed 4 feet without sacrificing drying efficiency. This means that the bin must be filled and emptied multiple times during the harvest season. Several companies now have in-bin drying systems that automatically remove the grain from the bin following drying and allow for automated refill from a wet holding tank.

Batch or continuous flow dryers are the most common type of grain drying equipment used for drying corn. These units have high airflow rates, monitored heat output, and limited grain depth across the drying chamber. Most units on the market are completely automated so that little operator oversight is necessary. Refill occurs from a wet holding tank on signal from the dryer. Dry grain is automatically discharged into an auger or elevator for movement into a grain bin. The advantages to these systems is that they are very efficient in drying grain to the desired moisture and they require little additional labor to operate the drying system. The disadvantage is that these systems usually cost more than in-bin systems and require grain handling systems to get the grain to and from the dryer.

In deciding which grain drying system is right for your operation, it is important that you determine the drying capacity in bushels per hour of each system and compare that to the speed at which you will be harvesting corn from the field. The volume of corn that can be dried per hour in in-bin systems is limited by the size of the drying bin and the speed at which it can be filled and emptied. This restriction often limits the amount of corn that can be harvested per day. Because they must be completely filled and emptied during the drying cycle, batch flow dryers are also restricted as to the volume of corn that can be dried per hour. Continuous flow systems offer the highest drying capacities of any system on the market. While the capacity of the grain handling system and wet holding tank can help increase the volume of grain handled by the drying system, there is a limited period over which wet grain should be stored before drying. Careful attention should be given to matching drying capacity with harvest speed. Few corn growers in North Carolina want to stop harvest due to limited drying capacity at a time when a major hurricane is threatening.

Grain Storage

There is one primary reason to store grain B to increase net return. If the net return cannot be increased by storing grain, storage is a waste of time and effort, and becomes a risk. The major drawback to grain storage can be summed up by the following. The returns from storage are measured in pennies, the losses from losing just one bin to insects or mold are measured in dollars. Fixed and variable costs associated with storing corn are shown in Table 2-9. While on-farm storage may appear to cost less when compared to commercial storage, there are other factors that must be considered. If grain is to be stored for a long period of time, if frequent monitoring of the grain is not possible, or if the labor and time required to move grain to the marketplace is not available when needed, then commercial storage may be a better alternative. The following questions should be used to determine if on-farm storage is necessary:

  • Are there sufficient commercial grain storage facilities?
  • During harvest, is transportation or storage a problem?
  • In the months following harvest, is it common for corn prices to increase sufficiently to cover storage cost?
  • Can weekly checks of stored grain be made and actions taken if necessary?
  • Can the grain be moved to the marketplace at any time of the year?

Table 2-9. Annual on-farm per bushel storage for corn.

Bin Capacity (bushels)
3,000 5,000 10,000 20,000
Cents per Bushel
Total Fixed Costs 10.4 8.4 5.9 4.7
Variable Costs
Electricity 0.8 0.8 0.8 0.8
Chemicals 2.0 2.0 2.0 2.0
Maintenance 4.2 3.7 2.5 2.0
Insurance 4.0 3.0 2.6 2.5
Labor 1.0 0.9 8.7 8.0
Total Variable Costs 12.0 10.4 8.7 8.0

Handling Stored Grain

Stored-grain management is a long-term approach to maintaining post-harvest grain quality, minimizing chemical control inputs, and preserving the integrity of the grain storage system. To implement an effective management program, operators must understand the ecology of the storage system. Storage management must focus on the following factors:

  • grain temperature
  • grain moisture
  • storage air relative humidity
  • storage time

An excellent preventive post-harvest grain management approach is the SLAM system (Sanitize/seal, Load, Aerate, Monitor). These stored grain management strategies should include the following steps.


  • Housekeeping - clean bins, aeration ducts, and auger trenches where insects thrive on dust and foreign material.
  • Cleanup - clean up around the bin removing weeds, trash, and moldy grain.
  • Disinfect - pesticide sprays or fumigation is important to remove all insects and molds.
  • Seal bin - seal all openings to provide barrier protection against insect entry at all locations below the roof eaves.


  • Load clean, dry grain - high levels of grain moisture increase the potential for high populations of stored-grain insects and molds. In North Carolina, corn stored for more than 6 months should be dried to 13.5% moisture. Table 2-10 shows the estimated storage times for shelled corn based on temperature and moisture content.
  • Core the grain - this involves operating the unload auger to pull the peak down and remove the center core of the bin that contains most fines and small foreign matter.
  • Spreading/Leveling grain - a level grain surface is easier to manage and less likely to change temperature during storage.

Table 2-10. Estimated storage times in days for shelled corn.

Moisture Content (%)
Temperature (F) 15 16 17 19 21 23 25
32 2672 1442 857 377 206 131 92
40 1398 754 448 197 108 68 38
50 491 265 155 69 39 26 21
60 275 148 85 39 22 16 10
70 154 83 49 22 12 8 5
80 86 47 28 12 7 4 3
90 48 26 15 7 4 2 2
100 27 15 9 4 3 1 1
Source: Oklahoma State University, Stored Product Management, Circular Number E-912, January 1995


  • Maintain grain temperature - grain temperature should be below 60°F to control insects and mold and should be reduced to the optimum storage level as early as possible following harvest. Grain temperature should be managed by aeration of grain in the fall, winter, and early spring. The aeration time necessary to achieve 60°F will vary with the airflow rates of the equipment used and ambient temperatures. Aeration can also reduce grain moisture content from 3 to 2 percent during one aeration cycle.
  • Use aeration to prevent moisture migration - in most grain bins, significant temperature differences develop within the grain mass causing moisture migration within the bin. These temperature differences are caused by changes in outside temperatures and humidity throughout the year and result in changes in the equilibrium moisture of the grain. Operators must constantly monitor grain condition particularly during periods of temperature change (fall or spring) to determine how temperature differences are effecting moisture migration in the bin. Aeration can be used to equalize grain temperature and moisture throughout the bin.


  • Use a grain thermometer to track grain temperature.
  • Schedule regular grain sampling and monitoring.
  • Fumigate as needed based on economic thresholds.
  • Aerate/turn hot spots when detected.

Corn Silage

Harvesting Corn Silage. Silage producers are more concerned about the tradeoff between silage quality and tonnage than they are about harvest losses. As in most cereal crops, the percent protein in the crop increases until the embryo is formed after which it declines. On the other hand, the energy content of the silage and total digestible nutrients are lowest during the period in which the embryo of the kernel is formed and then increases rapidly until black layer. Therefore, silage should be harvested according to quality requirements of the livestock feeder. For dairy producers who need higher protein, corn silage should be harvested just prior to early dent stage. This is the time when grain protein reaches its maximum content. For cattle feeders, corn silage should be harvested from early to mid dent stage. This helps improve protein levels with more energy and total tons of silage. In all cases, corn silage should be finely and uniformly chopped (particle length from : to 1 inch). Careful attention should be given to the sharpness of the knives and shear bar and to the setting of the shear bar. The uniformity and quality of the cut is directly related to silage quality and nutrient content.

Storing Corn Silage. There are a number of different storage systems suitable for corn silage. The four most common systems are open trench or pit, concrete stave silo, sealed silo, and silage bags.

Open trenches or pits are most commonly used because of their low cost, the ease of unloading, and the fact that corn silage can be harvested at 65 to 75 percent moisture. Corn silage in an open trench or pit should be tightly packed during the filling process to remove as much air space as possible. Once the pit is filled, the silage should be uniformly leveled and then covered with black plastic or other suitable cover. Many corn silage producers use a preservative such as salt or a commercial product on the top layer of corn silage to help in the fermentation process. Ground corn also works well as a fermentation stabilizer.

Concrete stave silos also are commonly used to store corn silage. These type of silos are filled from the top and equipped with an automatic unloading system. To properly store corn silage in a concrete stave silo the moisture content should be between 60 to 65 percent. Too much moisture will result in seeping. On the other hand, too little moisture results in poor fermentation and increased spoilage of the silage. Concrete stave silos are less expensive than sealed silos, but cost more to build and maintain than a pit silo or the use of silage bags.

Sealed silos are similar to concrete stave silos with the exception that they restrict the entry of oxygen into the silo. This results in a quick stabilization of the fermentation process and less spoilage. Silage moisture levels must be between 45 to 55 percent. The major drawback to sealed silos is the high cost of building and maintaining the silo.

Silage bags are polyurethane plastic bags approximately 12-15 feet in diameter. Silage is pressed into these bags by a special machine that moves forward automatically as the bag is filled. The process results in high quality forage because the fermentation process is controlled by the airtight bags and silage can be harvested at higher moisture levels (65 to 75 percent) without fear of seepage. The main drawbacks to silage bags are the cost of the bag and bagging equipment, the tendency for the bags to tear or rip, and the difficulty in removing the silage from the bag. The cost of silage bags, including the bagger, is less than either a concrete stave or sealed silo, but greater than a pit silo.

The method of storage for corn silage should be selected based on the value of quality forage, the labor available, and cost. Whichever storage system is selected, the key to proper silage storage is the moisture level of the silage at the time it is harvested. Use of a silage moisture tester is vital in determining when to cut corn silage for each storage system. Even 1 or 2 percent more or less moisture than recommended for the system could result in severe losses due to seepage or spoilage.

Figure 2-5. Per bushel drying costs.

Figure 2-5. Per bushel drying costs.


Professor and Extension Specialist, Corn/Soybeans/Small Grains
Crop and Soil Sciences
Professor Emeritus
Crop and Soil Sciences
Professor and Extension Soybean Specialist
Crop and Soil Sciences

Publication date: Jan. 1, 2003

North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.