By David Karki
Winter wheat possesses an excellent physiological mechanism to survive the harshest of the winter conditions. Overwintering, or winter survival, of winter wheat is a long process that starts in the late fall with the decrease in daily temperatures, and it is completed when it starts its regrowth the subsequent spring. Factors, such as genetics, amount of snow cover or insulation and winter temperatures, can all play a significant role in winter survival of a wheat crop.
The weekly crop progress report on April 18, 2021 rated 3% of winter wheat crops to be in ‘very poor’ condition, 16% in poor, 45% in fair, 35% good and 1% excellent condition. The 2021 prospective plantings published in March by the U.S. Department of Agriculture National Agricultural Statistics Service (USDA NASS) estimated 760,000 acres of winter wheat were planted in South Dakota. Compared to previous years, fall of 2020 was unusually dry in South Dakota, which, in one hand, allowed growers to seed their winter wheat in a timely fashion, but, on the other hand, the fall growth was not ideal in most part due to limited moisture. Plants with two to three tillers before prolonged freezing or before plants go to dormancy are considered ideal. Another factor that plays a vital role in a plant’s ability to withstand harsh winter conditions is protection from field residue and insulation from snow. The 2020–21 winter did not receive the usual amount of snow, and fields were very open (without snow insulation) in many parts of South Dakota. Open fields, when coupled with daily high temperatures in negative degrees Fahrenheit for a long stretch in February 2021, could easily cause winterkill in overwintering crops, like winter wheat. Ideally, winter wheat resumes rapid growth when temperatures gradually rise in spring. In years when producers see uneven spring stand, an accurate estimate of plant stand is needed to properly assess the field. Fields that are few miles apart can have substantially different plant stand, so, it is necessary to go through the fields thoroughly before deciding on keeping the crop or planting spring/summer crop in those fields.
Typically, the number of plants in one-foot row are counted and converted to plants per-square-foot. The length of row equaling to a square foot can be different for different row spacing. For example, for six-inch spacing, two-foot row equals one square foot, for seven-inch spacing, 1.7 feet equals one square foot, and for 7.5-inch spacing, 1.6 feet row equals one square foot. Plant stand needs to be assessed at least five or more places in the field, and only the ‘average’ of all counts is used to estimate the final stand. The recommended planting density is 1.2 million live seeds per square foot, which equals to 28 live plants per square foot. One thing to keep in mind is percent loss in the stand does not always reflect the exact percent loss in potential yield, because plants tend to put more growth (and tillers) and thrive when plant-to-plant competition is low, compensating for that loss of stand. When weather and other growing conditions are good, 80% to 90% stand can still reach 100% yield potential. This makes the decision difficult or ‘tricky’ while deciding if the winter wheat fields need to be planted to some other spring crops. Although it’s a personal preference, the rule-of-thumb is if the stand in the spring is less than 14 plants per square foot, or less than 50% of the expected stand, then the field should be planted to another crop. Economics of potential yield loss and the expense of the second crop is the driving factor while making the decision. Short- and long-term weather outlook, as well as crop insurance options, may also play a role in what type of crop to plant in those fields.Source : sdstate.edu