December 5, 2008

Charles Shapiro, Extension Soils and Nutrient Management Specialist

Corn growers need to set a realistic corn yield goal to make sound decisions on corn hybrid, seeding rate, fertilizer application, and irrigation need. The goal should be the most profitable yield that can be expected for the particular set of soil, climate, and management practices. Yield goals should gradually increase over time, but cannot exceed the theoretical yield potential. Attainable yields differ between irrigated and dryland environments, which must be considered for setting yield goals.

In well-managed irrigated corn, the attainable yield is close to the yield potential and relatively stable from year to year because irrigation is provided during key growth stages to make up for water deficits. In dryland corn, the attainable yield is typically less than that for irrigated corn, but fluctuates widely, depending on the initial soil moisture status, soil water holding capacity, planting date, plant density, and rainfall during the growing season. At any given location, weather differences among years cause common ranges of the attainable yield of about 40 bu/ac for irrigated corn and 40 to 80 bu/ac for dryland corn.

The yield goal should reflect what can be grown if normal weather prevails and good management is achieved. Consider past yields field by field and perhaps by management areas within the field for setting yield goals. A yield goal should not exceed the attainable climatic yield potential of corn, which varies across geographical regions and among years (Table 1). If your soil has limited potential, recognize it and try to alleviate problems such as nutrient deficiencies or compaction.

Irrigated Corn

The yield goal should be within 105% to 110% of the average of the past five corn seasons harvested and 80-90% of the attainable yield shown in Table 1. When calculating the five-year yield average, only use years with relatively normal weather conditions and no unusual events that may have caused extremely low or high yields. Compare your yield goal with good corn yields that have been achieved in your area. Be reasonably optimistic in setting your yield goal. Do not continue to set yield goals at 220 bu/ac if you are consistently producing only 160 or 180 bu/ac. The soil or weather conditions or your management practices may simply not have the potential to produce 220 bu/ac.

Dryland Corn in Eastern Nebraska

The yield goal should be within 105% to 110% of the five- to ten-year yield average and not more than 80%-90% of the attainable water-limited yield shown in Table 1. Dryland corn yields mainly reflect precipitation patterns in the state, with highest yields in the eastern areas. The dryland grower also should consider the moisture status at planting time when setting the yield goal. For example, if only the top 3 feet of soil is moist and rainfall during the growing season is predicted to be lower than normal, the yield goal should be reduced from that of a fully moist root zone. In this case, both seeding and fertilizer rates should be reduced accordingly. Be prepared to change the yield goal right up to planting and through sidedressing. Delay application of some nitrogen to maintain flexibility in matching nitrogen rates to revised yield goals.

How Table 1 was Calculated

Daily weather data and crop statistics on average planting and maturity dates of corn during the past 20 years were used in the Hybrid-Maize model to estimate the yield potential and the attainable water-limited yield of corn for each year at 35 Nebraska locations (Table 1). Hybrid-Maize, a component of the UNL Soil Fertility and Nutrient Management Web site, simulates the growth and maximum yield potential of fully irrigated and fertilized corn as a function of seasonal temperature and solar radiation for a particular planting date, hybrid maturity group, and final plant density. In addition, rainfall and soil type (texture) are taken into account for simulating the attainable yield of dryland corn, limited only by rainfall. Table 1 shows averages for major regions in Nebraska and the common ranges that occur in 50% of all years.

Example: A Farm in Clay County. The estimated attainable yield for the typical climate at this location is 255 bu/ac for irrigated corn with final stands of 30,000 plants per acre (Table 1). Therefore, the yield goal should be within a range of 204 to 230 bu/acre (255 x 0.8 to 255 x 0.9). Actual yields were: 1996 – 194 bu/ac; 1998 – 186 bu/ac; 1999 – 232 bu/ac; 2000 – 155 bu/ac; 2001 – 190 bu/ac; 2002 – 206 bu/ac; and 2003 – 212 bu/ac. In 1999, the growing season was exceptionally long, resulting in much higher than normal yield. Yield in 2000 was exceptionally low due to extreme heat and insufficient irrigation. The five-year average yield is calculated without these two extreme years and equals 198 bu/ac (194 + 186 + 212 + 190 + 206)/5. Based on the past yield, the new yield goal is 198 x 1.05 or 198 x 1.1 = 208 to 215 bu/ac, which is within the calculated attainable yield range. 

If yield goals determined by historical production data are different than the calculated attainable yield, examine management details to determine the cause.

Resource

For further information, check NebGuide G481, Setting a Realistic Corn Yield Goal, available online at extension.unl.edu/publications.

Acknowledgement

Achim Dobermann, the original lead author of the NebGuide on this topic, is no longer on the UNL faculty. We acknowledge his contributions to the first edition of this publication and to the Hybrid-Maize model on which this publication is based.