Introduction

Corn seed companies provided 43 hybrids that were part of the official variety trials on several LSU AgCenter research stations during 2016. Seven hybrid trials were conducted at four AgCenter research stations across the state.

In addition to those research station tests, the on-farm core block demonstrations were conducted with a total of 13 hybrids planted over 11 locations in the corn-growing areas of Louisiana. LSU AgCenter extension agents coordinated these demonstrations.

The official corn hybrid trials were conducted according to AgCenter best management practices. The on-farm core block demonstrations were placed with corn producers and subjected to the standard production practices for each producer.

On-farm core block demonstration information is presented to provide yield results by trial, as well as 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. Sufficient trials were conducted across a variety of locations, however, so meaningful and relevant observations can be made that will be useful to Louisiana producers as they make hybrid selection decisions.

The data provided in this publication should help you make more informed decisions about which hybrids will perform best for your production area.

Hybrid Selection

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 neighboring growers. Some hybrids tend to perform better than others based on soil type, planting date, environmental conditions and location.

Relative maturity is determined genetically, but maturity date of a given hybrid depends on the daily temperature mean accumulation (growing degree units) above 50° F for corn. Below that temperature, minimal corn growth occurs. Louisiana producers can grow early hybrids (100-108 days), midseason hybrids (109-119 days) and full-season hybrids (more than 120 days).

Plant height, ear height and stalk strength are factors that influence corn stands and, ultimately, yield. Husk cover is important in wet harvest seasons because loosely shucked hybrids may dry quicker. Loosely shucked hybrids tend not to withstand a wetter, more humid Louisiana harvest season as well as the thicker, tightly shucked ones. Grain quality can be affected as can the susceptibility to pathogen.

Planting Rate and Depth

The optimal plant population for corn ranges from 25,000-30,000 live plants per acre. Assume 80 percent field emergence if planting early (plant 31,250-37,500 seeds per acre). The lower end of the recommended range should be used when lower yields are expected due to 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.

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 more than 2 inches deep can increase the probability of an uneven plant stand, which can affect growth and yield.

Fertilization

Proper fertility is critical for optimizing crop yields, particularly in corn. Soil pH should be at least 5.8 for corn production. 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 1).

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.

Banding phosphorus will increase its efficiency when the soil pH is very acidic or alkaline or when soil test phosphorus levels are low. Soil testing is recommended to apply appropriate levels for each field, but in many soils, 40-60 pounds of P2O5 and K2O per acre will be needed. Corn uses phosphorus and potassium early in its growth cycle, so these nutrients should be applied preplant or at planting.

Soil testing also is recommended for determining sulfur and zinc needs. If sulfur is lower than 12 parts per million (Mehlich 3), apply at least 10 pounds of sulfur – in the sulfate form – per acre. 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. 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, thus 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 (0.7-98.3 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.

Planting Date

Corn should be planted as close as possible to the date of the average last spring freeze. The optimal planting window for south Louisiana is from Feb. 25 to March 20, and for north Louisiana the optimal planting window generally is March 10 to April 1. In most years, April 15 is the last date for maximum yield potential. Extending planting to May 1 can result in a yield reduction of 30 percent or more.

Corn younger than V6 (6-leaf stage) usually can withstand a light frost if the temperature does not drop below 30° F. A moderate freeze will burn any existing leaves and cause them to drop, but new leaves can emerge in four to five days with warmer temperatures. However, as the growing point moves upward near the soil surface the possibility of injury increases.

Evaluating the Data

This report begins with yield data from the official variety trials conducted by LSU AgCenter scientists in a replicated format that allow for statistical comparisons (tables 2 and 3). Detailed 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 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 that best represents 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 4-15). 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.

See PDF for tables.