Daniel Fromme, May, Dana, Shannon, Keith
This year, commercial corn seed companies provided 51 hybrids that were entered in the official variety trials. Five hybrid trials were conducted at four AgCenter research stations located throughout the state. Commercial seed companies voluntarily entered and selected the hybrids they wanted to have evaluated by the AgCenter.
In addition to the research station tests, the on-farm core block demonstrations were conducted with a total of 11 hybrids planted at 16 locations throughout the corn-growing areas of Louisiana. LSU AgCenter extension agents coordinated these demonstrations.
The official corn hybrid trials were conducted according to LSU AgCenter best management practices. The on-farm core block demonstrations were placed with corn producers and subjected to their standard production practices.
On-farm core block demonstration results are presented to provide yield results by trial and trend comparisons from the compiled data. As opposed to the official variety trial research, core block demonstrations sometimes are not replicated in the field, and a rigorous statistical analysis is not possible. However, sufficient trials were conducted across a variety of locations; therefore, meaningful and relevant observations can be made that will be useful to Louisiana producers as they make hybrid selection decisions.
In conclusion, the LSU AgCenter corn hybrid trials provide the most complete and unbiased source of information on yield comparisons. The data provided in this publication should help you make more informed decisions about which hybrids will perform best for your production area.
Evaluating the Data
This publication includes yield data from the official variety trials conducted by LSU AgCenter scientists in a replicated format that allows for statistical comparisons (Tables 10-11). Detailed plant growth measurements were made, but this report only displays yield data. For a complete review of the official variety trial data, visit the corn section of the LSU AgCenter’s website at www.lsuagcenter.com/corn.
For a better understanding of how corn hybrids performed in Louisiana, refer to the official variety trial data first. Choose the hybrids that performed well overall and those that performed well in the region most representative of your growing area. Finally, check the on-farm core block data to see if it is consistent with the official variety trial data for your chosen hybrids (Tables 12-28). By making thorough comparisons across the full range of information available, you can improve your chances of choosing hybrids that will perform well on your farm.
Hybrid selection is one of the most important decisions a producer will make and is essential for successful corn production. Seed companies offer multiple hybrids for sale to producers for good reasons. Each corn producer has somewhat different soil conditions, irrigation practices and crop rotations than other growers located in their farming community. Some hybrids will tend to perform better than others based on soil type, planting date, environmental conditions and location.
Yield is important when selecting a corn hybrid; however, maturity, stay-green, lodging, shuck cover, ear placement and disease and insect resistance need to be considered. Yield data from multiple locations and years are good indicators of the consistency of a hybrid’s performance.
Hybrid maturity is rated using the relative maturity (RM) or growing degree day (GDD) rating systems. These two methods are based on the number of days or degree days for a hybrid to reach physiological maturity. Louisiana producers can grow early, midseason, and full-season hybrids. In Louisiana, 112-to-121-day maturity hybrids usually produce the best yields. Full-season hybrids do not consistently out yield midseason hybrids. It appears there is more variability in yield among hybrids within a given RM rating than there is between maturity groups.
Hybrids that stay green later into their maturity usually retain better stalk strength and have less lodging potential. Shuck cover is important for protecting the ear and kernels from weathering and fungi. At later planting dates, a corn hybrid will grow taller because of an increase in day and night temperatures, causing the internodes of the stalks to be longer. Therefore, ear placement will be higher when compared to an earlier planting date. This usually means that the lodging potential will be greater. When planting late in the season, consider planting a hybrid that has a low ear placement.
Also, corn hybrids have different insect and herbicide traits. These biotechnology traits will need to be considered and should be based on which one best fits into your production system.
Select several hybrids that are consistently top performers over multiple locations or years within a region. Consistency over multiple environments is important because we cannot predict next year’s growing conditions.
Corn growth and development responds to temperature and is not controlled by day length. Thus, the calendar date is not as important as soil temperature and air temperature when considering to plant corn. Good germination and emergence are expected when the soil temperature at a 2-inch depth is 55 degrees Fahrenheit by 9 a.m. for three consecutive days. This normally occurs in late February and March in Louisiana. In most years, the optimal planting window for south Louisiana is Feb. 25-March 20, and for north Louisiana the optimal planting window generally is March 10-April 1. Extending planting past the last optimal planting date can result in losses of half of a bushel to 1 bushel per day.
Frost may occur after these planting dates in some years; however, corn typically withstands frost with little economic injury. Corn younger than V6 (six-leaf stage) usually can withstand a light frost if the temperature does not drop below 30 degrees Fahrenheit. A moderate freeze will burn any existing leaves and cause them to drop, but new leaves can emerge in four to five days with warm temperatures. However, as the growing point moves upward near the soil surface, the possibility of injury increases.
Planting Rate and Depth
The optimal plant population for corn ranges from 27,000 to 30,000 live plants per acre. At 80 percent field emergence, this would equate to planting 33,750-37,500 seeds per acre. The lower end of the recommended range should be used when lower yields are expected because of soil type, late planting date, drought-prone areas or low fertility. Higher populations should be used on highly productive deep alluvial soils or irrigated fields where moisture will not be a limiting factor.
Also, seeding densities can be affected by “ear flex.” Full-flex hybrids can compensate for fewer plants per acre because the ear grows both in length and girth. These hybrids usually produce only one ear per stalk. Individual semi-flex hybrid ears will not compensate to the extent that full flex hybrids will, but with low-stand density and excellent growing conditions, they may set two or more ears. Fixed-ear hybrids must obtain the desired population for maximum yields.
Seed size and shape are not critical for a good stand, but be sure to use the correct plate and planter for the size purchased. Corn should be planted 2 inches deep. It is vitally important to establish seed contact with moist soil, but planting seeds greater than 2 inches deep can increase the probability of an uneven plant stand, which can affect growth and yield.
Corn Growth and Development
Corn growth and development is closely related to temperature. Warmer temperatures mean faster corn growth, and cooler temperatures mean slower corn development.
Temperatures are used to calculate growing degree days (GDD), which some people call heat units (HU). Several formulas exist to calculate these GDD, but the one used most often is the modified 86/50 cutoff method (MGDD).
MGDD for any given day is calculated by subtracting 50 from the average daily temperature. The average daily temperature is calculated by adding the daily high and the daily low temperatures and then dividing by two.
GDD = Max. Temp + Min. Temp. – 50F
Two criteria or rules exist when calculating MGDD. First, if the daily high was greater than 86 degrees Fahrenheit, then 86 is used to calculate the average. Second, if the daily low was less than 50 degrees Fahrenheit, then 50 is used to calculate the average. These upper and lower temperature thresholds or limits define the boundaries beyond which corn develops very slowly, if at all.
Throughout the years we have talked about the number of MGDD accumulation when silking or physiological maturity (black layer) occurs. For example, a particular hybrid will silk at 1,365 MGDD or reach physiological maturity at 2,800 MGDD.
Another useful purpose for following MGDD accumulation is to track the rate of leaf development prior to pollination. From V1 to V10, new leaves (defined by the appearance of leaf collars) emerge at a rate of about 85 MGDD per leaf. This is equivalent to about one leaf every five to six days in early April. From V10 to the final leaf, leaves emerge at a rate of about 50 MGDD per leaf.
Practical uses of this information include estimating how far along the corn crop should be for any given location if we know the planting date and the MGDD accumulations since the planting date. It is especially important to know the emergence date, but if this is not available we can use 125 MGDD from planting to emergence if the actual date is not known.
For instance, corn should reach the V6 growth stage by the time 635 MGDD have accumulated since planting. This is calculated by using 125 MGDD from planting to emergence, then figuring 510 MGDD (6 x 85) from emergence to V6.
It is very important to remember that a shortage of MGDD resulting from early season cool temperatures can never be recovered. Midsummer days in the 90s do not necessarily accelerate MGDD accumulations because rate of growth is minimal when temperatures are above 86 degrees Fahrenheit.
Also, plant stress (soil compaction, excessive soil moisture, pest injury, hail damage) can interfere with this relationship and retard leaf development. Comparisons of predicted leaf development stages with actual leaf stages can therefore be used as an indicator of plant stress.
Soil testing is the foundation of a sound fertility program. This is the only way for a crop manager to efficiently apply the correct rates of lime and fertilizer. Proper fertility is critical for optimizing crop yields, particularly in corn. Seldom is there a field that does not require the addition of fertilizer. The estimated uptake of N, P, K and S by a 200-bushel-per-acre corn crop is presented in Table 1. Be aware that the values presented are not the amounts of nutrients that need to be applied, but rather the total uptake by the corn crop from soil, fertilizer and other sources.
Soil pH affects the availability of nutrients to plant roots. The desirable soil pH for corn ranges from 5.8 to 7.0. Continued cultivation and the use of chemical fertilizers, especially those containing ammonium and sulfur, tend to decrease soil pH over time. Irrigation with water high in calcium carbonate, on the other hand, tends to increase soil pH.
Soil samples should be collected and checked for the degree of acidity or alkalinity. Lime is generally recommended at pH values below 6.1 (Table 2). Recommendations in Table 2 are general guidelines to raise pH. Soil texture and the buffer capacity of the soil are required for a more accurate estimate of the amount of lime that is needed. If lime is needed, it is recommended to apply it during the fall to provide enough time for it to react with the soil.
The relative neutralizing material (RNV) of lime impacts the amount that is needed to be applied. The RNV of a material is based on its fineness and calcium carbonate equivalent (CCE or the amount of pure calcium carbonate to which the selected material corresponds), with finer materials reacting more quickly than coarse materials. An ag lime material with a CCE of 100 is “stronger” than an ag lime material with a CCE of 90. Consequently, less volume would be needed to increase the pH of a given soil.
Nitrogen is necessary for chlorophyll synthesis and is part of the chlorophyll molecule involved in photosynthesis.Lack of N and chlorophyll means the crop will not utilize sunlight as an energy source to carry on essential functions, such as nutrient uptake. It is an essential component of amino acids, which form plant proteins. Thus, N is directly responsible for increasing protein content.
A rough rule of thumb is to apply 1 to 1.2 pounds of actual N for each bushel of corn produced. Nitrogen should be applied according to whether the field is an alluvial plain, such as the Delta, or an upland soil and whether it is irrigated or dryland (Table 3).
Apply nitrogen in a split application with 50-75 percent applied before or at planting and the balance when corn is 3-12 inches tall. All the nitrogen can be applied preplant or at planting, but this increases the risk of fertilizer burn on seedlings and nitrogen loss from leaching or volatilization. An application of 20-50 pounds of nitrogen at tassel may be beneficial if environmental conditions resulted in leaching or volatilization of nitrogen.
Phosphorus plays a role in photosynthesis, respiration, energy storage and transfer, cell division and cell enlargement in the plant. It promotes early root formation and growth, increases water-use efficiency and hastens maturity.
Corn uses phosphorus early in its growth cycle, so these nutrients should be applied preplant or at planting (Table 4). Banding phosphorus will increase its efficiency when the soil pH is very acidic or alkaline or when soil tests reveal phosphorus levels are low. Also, starter fertilizers can be beneficial for soils that have a high pH or have very low to low phosphorus levels.
Soil testing is recommended to apply appropriate levels for each field, but in many soils 40-60 pounds of P2O5 per acre will be needed.
Potassium is vital to photosynthesis. When K is deficient, photosynthesis declines and the plant’s respiration increases, which reduces the plant’s carbohydrate supply. Other functions of K include that it is essential for protein synthesis, helps control ionic balance, translocation of heavy metals, helps overcome the effects of disease and is involved in the activation of 60 enzyme systems. Potash deficiency in corn results in reduced growth, delayed maturity and lodging.
Corn uses potassium early in its growth cycle, so these nutrients should be applied preplant or at planting (Tables 5-8). Soil testing is recommended to apply appropriate levels for each field, but in many soils 40-60 pounds of K2O per acre will be needed.
Sulfur is part of every living cell and is a constituent of two of the 21 amino acids that form proteins. Sulfur is often overlooked in a soil fertility program. Increased crop yields, reduced sulfur emissions from industrial chemical facilities, increased use of higher analysis fertilizers and a greater awareness of the importance of sulfur to corn production are contributing to an increased need for sulfur fertilization.
A typical 200-bushel-per-acre corn crop takes up about 30 pounds per acre, with about 16 pounds per acre removed in the grain at harvest. When a soil test is utilized to determine if sulfur is needed, values of less than 12 ppm (Mehlich 3) generally suggest that additional sulfur may be needed. Typical recommended rate is 20 pounds of sulfur in the sulfate form per acre.
Zinc was one of the first micronutrients recognized as essential for plants and the one most commonly limiting yield. Although it is required in small amounts, high yields are impossible without it. Corn is one of the most responsive crops to zinc applications.
If zinc is lower than 1 ppm, apply 10 pounds of zinc in a soluble form, such as zinc sulfate or zinc chelate, per acre (Table 9). Among the inorganic zinc sources on the market, the most common sources are sulfates, oxides, and oxysulfates. Zinc sulfate and zinc chelates essentially are 100 percent water-soluble, while zinc oxides essentially are insoluble in a single crop season and therefore are unavailable to the crop to be planted. Oxysulfates are a mixture of sulfates and oxides, with varying proportions of sulfates and oxides and different solubility levels (0.7 percent to 98.3 percent). The effectiveness of these can be highly variable, depending on solubility. Low-solubility materials may have some value in a long-term buildup program, but when immediate results are the goal, highly soluble fertilizers are the best choices. For acceptable in-season efficacy, a zinc-fertilizer source should be at least 50 percent water-soluble. If a soil test shows zinc is between 1 and 2.25 ppm, apply 5 pounds of zinc per acre when broadcasting. Less is needed if using a banded application.