It was wonderful to wake up to the sound of rain on the window pane last Friday.

We need about another inch per week for the next five or six weeks.

The combination of high temperatures and inadequate moisture has created severe stress in many cornfields. Weather conditions are inhibiting root development. In addition to water deficits, high soil temperatures are limiting root growth near the soil surface. The corn canopy shades the soil surface and moderates soil
temperatures, but many cornfields have yet to canopy. Plants with root systems restricted to the upper four to five inches of the soil profile are stunted.

Yield losses can be directly related to the number of days that the crop shows stress symptoms during different growth periods. According to OSU Extension Corn Specialist Peter Thomison, Iowa research by Claassen and Shaw shows drought stress during early vegetative growth usually has a negligible impact on grain yield.
Some corn agronomists contend that mild drought during June may even be beneficial because roots generally grow downward more strongly as surface soils dry, and the crop benefits from the greater amount of sunlight that accompanies dry weather. During later vegetative stages, when kernel numbers per ear are determined, plants become more sensitive to stress.

According to Claassen and Shaw’s findings, four days of stress, corn wilted for four consecutive days, at the 12th–14th leaf stage, has the potential of reducing yields by 5-10 percent. Kernel row numbers on the ear are determined by the 12th collared leaf stage and the potential number of kernels per row is complete about one week before silking. Thomison said, corn planted in April and early May will reach tasseling, silking and pollination in about 2 to 3 weeks. To get a better understanding of why this period is so sensitive to drought, consider the water requirements of corn shown below.

A corn crop in Ohio typically uses 20 to 22 inches of water during the growing season and water requirement vary according to the stage of development. Corn reaches its peak water use during pollination when plants are silking. Alfalfa usually has a strong capacity to continue growth under dry conditions, and we would normally expect alfalfa to be growing better than it is at this stage in a dry cycle.

Unfortunately, the late killing spring frost this year resulted in alfalfa plants having to initiate new growth all over again. That required a lot of energy from the plant at a time when taproot reserves were low. This has likely contributed to the weak regrowth of many alfalfa stands, especially those that were cut last autumn or have additional stress factors. Alfalfa stems stop growing during the initial phases of moisture stress, but the plant continues to manufacture carbohydrates and protein that are stored in the root system.  Allowing those reserves to accumulate a little longer will benefit alfalfa plant health and longevity.

This farm news was published in the June 27, 2007 issue of Farm World, serving Indiana, Ohio, Illinois, Kentucky, Michigan and Tennessee.