08/01/2015: Winter wheat - cold hardening examined

With roller-coaster temperatures the past couple of winters, it helps to know how winter wheat typically survives the winter, AgriView reports.

Winter wheat is never truly dormant, but it does gradually go through cold acclimation in the fall until it is able to withstand cold temperatures — down to a point, said Jim Shroyer, Kansas State University crop production specialist emeritus. During the fall, winter-wheat seedlings spend the first month or so developing their first leaves, the crown and a secondary root system. All the while, the seedlings are building and storing energy they will need to go through the cold acclimation process and survive winter.

Normally seedlings need at least two to three true leaves and a tiller or two to have built up enough stored-energy reserves to survive winter. Seedlings will have a better chance of winter survival if their crowns are well developed in firm soil, about a half-inch below the soil surface, Shroyer said. Winter hardiness or cold tolerance is a physiological process triggered by gradually cooling temperatures in the fall.

During the process of cold acclimation, certain genes within winter wheat begin to initiate the production of anti-freeze-type substances to protect the cell membranes. The process of cold acclimation within a sufficiently developed wheat seedling begins when soil temperatures at crown depth fall below about 50 degrees.

Photoperiod also plays a role in the process of cold hardening, with shorter days and longer nights helping initiate the process. Winter survival depends on the crown remaining alive, and the substances that produce cold acclimation are most needed within the crown. It takes about four to six weeks of soil temperatures below 50 degrees at the depth of the crown for winter wheat to fully cold harden.

The colder the soil at the depth of the crown, the more quickly the plants will develop winter hardiness. Cold hardiness is not a static state, however. After the cold-hardening process begins in the fall, wheat plants can rapidly unharden when soil temperatures at the depth of the crown rise above 50 degrees. The plants will then re-harden as crown temperatures cool below 50 degrees again. By the time winter begins, winter wheat will have reached its maximum level of cold hardiness.

Once winter wheat has reached the level of full cold hardiness, it will remain cold-hardy as long as crown temperatures remain below about 32 degrees, assuming the plants had a good supply of energy going into the winter.

If soil temperatures at the crown depth rise to 50 degrees or more for a prolonged period, there will be a gradual loss of cold hardiness. The warmer the crown temperature during the winter, the more quickly the plants will start losing their maximum level of cold hardiness.

Winter wheat can re-harden during the winter if it loses its full level of winter hardiness, but it will not regain its maximum level of winter hardiness. Even at its maximum level of winter hardiness, winter wheat can still be injured or even killed by cold temperatures if temperatures at the crown level reach single digits.

There are varietal differences in winter hardiness. As soil temperatures at the crown level rise to 50 degrees or more, usually in late winter or spring, winter wheat will gradually lose its winter hardiness entirely.

Photoperiod also plays a role in this process. When the leaves switch from being prostrate to upright, the plants will have completely dehardened.

Read the article HERE.

 

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