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Heat waves combined with poor air quality in western areas this growing season may have an effect on corn yield potential and silage quality. Corn may appear to be shorter and maturing faster under these conditions.
High temperatures, even in conjunction with sufficient moisture, can cause a high degree of stress on the corn plant. Both daytime and nighttime high temperatures can have an effect on corn yield potential and silage quality. Corn is a tropical grass and can withstand temperatures as high as 112 °F for brief periods.1 The optimal daytime temperatures for corn growth typically range between 77 °F and 91 °F, with growth decreasing when temperatures exceed 95 °F. Iowa State University reports that a 1% corn yield loss can occur after four consecutive days of temperatures at 93 °F or greater.2 On the fifth day, another 2% yield loss can occur, and on the sixth day, another 4% can be expected. A heat wave lasting a week or more often results in the firing of leaves and lowered yield potential expectations, especially when the heat wave coincides with silking. Respiration is stimulated by high temperatures and uses sugars that would otherwise have been allocated to grain. This occurs when nighttime temperatures remain high and sugars are being used while no photosynthesis takes place. Thus, high nighttime temperatures can reduce yield potential without plants showing visible signs of stress.3 That being said, corn may be able to tolerate heat better under western conditions with high solar radiation, irrigation, and low humidity.
Nighttime temperatures can be the key factor as to how much the corn plant will be affected by heat stress. High nighttime temperatures in the 70s and 80s can result in wasteful respiration lowering the amount of dry matter accumulation.1 The rate of plant respiration can increase rapidly with higher temperatures, doubling for each 13 °F increase. Sugars that had been produced through photosynthesis during the day can be lost and no longer available for grain fill. In addition, high nighttime temperatures can result in faster heat unit (GDU) accumulation that can lead to earlier corn maturation. Cool nighttime temperatures slow GDU accumulation, lengthens grain fill, increases dry matter, and improves yield potential.
Heat stress can reduce yield potential in irrigated corn due to the following:4
Heat and drought stress are often considered to be interrelated. Under irrigated conditions, it can be likely that plants are under temporary drought stress right before the next irrigation. To help determine whether plants are undergoing heat stress or a combination of heat and drought stress, evaluate leaves early in the morning while temperatures are low. If leaves are curled while soil moisture is adequate, symptoms are most likely caused by heat stress.
Heat stress affects pollen production; whereas, silk development is more affected by drought stress. Heat stress has an adverse effect on the development of viable pollen, limiting pollination, and can also limit kernel development after ovules have been fertilized. Heat stress during this period can limit starch accumulation within the kernels and increase the rate of kernel abortion. Ultimately, heat stress can affect silage quality by reducing fiber digestibility.5
Other abiotic stress factors such as particulate matter from dust and forest fires can further exacerbate the effects of heat stress by reducing solar radiation and the rate of photosynthesis. Long periods of smoky conditions caused by wildfires during the reproductive growth of corn (especially from R2 to the R4 stage) can limit kernel development and result in shorter ears. Any stress that affects the grain portion (ear size and fill) or grain/stover ratio can lead to reduced grain yield potential or a silage crop that is low in digestibility and nutritional quality.
Although heat and other abiotic stresses are not controllable, management practices, such as corn product selection and planting date, should be considered to avoid silking and early kernel development during periods of very high temperatures. Planting a diverse portfolio of corn products using a range of relative maturities and planting dates can help to reduce the overall risk from abiotic stress factors.