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Indiana corn crop finishes pollination, grain fill begins

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Written Thursday, August 12, 2010  

Indiana's corn crop has finished pollination and moved on to the process of grain fill, a period of 45-60 days when kernel set and weight are determined.

"The grain fill period begins with successful pollination and initiation of kernel development and ends approximately 60 days later when the kernels are physiologically mature," said Bob Nielsen, Purdue Extension corn specialist.

During this time, the plant will give precedence to the photosynthate needs of the developing kernels, sometimes at the expense of the health of other parts of the plant such as the roots and lower stalk.

This season's early planting and above-average temperatures made way for what could be an early maturity date for much of the crop. According to Nielsen, silking progress so far has been on par with the record-setting earliness of the 2004 growing season. Earlier maturity dates make it more likely that grain will have more rapid drydown in the fields before harvest, compared with the wet harvest conditions corn farmers experienced in 2009.

Part of what leads to a successful grain fill period and maximum yield is minimal plant stress.

"Severe stress during grain fill can cause kernel abortion or lightweight grain and encourage the development of stalk rot," Nielsen said. "The health of the upper leaf canopy is particularly important for achieving maximum grain filling capacity."

Right now in Indiana there are still many damaged and stunted fields from root damage after lengthy periods of saturated soils in late spring. The heavy rains that saturated soils also meant the root systems are more shallow.

"If the rain 'spigot' would shut off for the remainder of the grain fill period, droughtlike symptoms would quickly develop and take their toll on kernel survival and weight," Nielsen said.

Conditions this growing season also have been favorable for early infection of some corn foliar diseases, including gray leaf spot. Nielsen said significant loss of photosynthetically active leaf area from diseases, drought, nitrogen deficiency or hail damage during the grain fill period would weaken stalk integrity and increase plants' susceptibility to root and stalk rot organisms.

Nielsen pointed out that above-normal temperatures during grain fill are less than ideal for optimum yield.

"Excessively warm temperatures encourage a faster grain filling rate per day, which is good, but a shorter grain filling time period, which is not good," he said. "The abbreviated length of the grain filling period during warm temperatures tends to outweigh the benefits of faster daily grain filling rates."

Despite the less-than-ideal weather conditions, soil moisture has remained adequate and many plants have remained healthy. If soil moisture persists and plants stay healthy, Nielsen said there is tremendous yield potential in many of Indiana's corn fields--especially if temperatures moderate soon.

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