Winter Wheat: Fertility Requirements and Assessing Survival
- Winter Wheat
Spring is right around the corner, and it’s that time of year when winter wheat growers are starting to think about spring fertility requirements and how their crop survived our Manitoba winter. Ideally, the optimum plant stand is over 20 healthy plants per square foot, but keep in mind that a stand of 10 to 15 plants per square foot can still produce a profitable crop. There are three common ways to assess winter wheat survival:
- Spring growth: Likely the most common, this method requires that farmers wait until their winter wheat crop has broken dormancy and new growth is initiated in the field. Start by digging up plants in various spots in the field (i.e., areas that had different levels of residue and snow cover). The plant roots should be rinsed and examined for new root growth and a healthy white crown. Count the plants per square foot that have these characteristics and keep in mind that plants showing signs of leaf burn or that are brown in colour do not necessarily indicate winterkill.
- Bag test: First, plants are dug up with caution not to damage the crown. After rinsing the crown and roots, the roots and leaves should be trimmed, leaving one inch of stem above the crown. Place the crowns in a Ziploc bag and keep at room temperature. Repeat the rinsing and allow new air into the bag every two days. Healthy plants will grow new leaves and roots. If no new growth is observed after six days, consider it a victim of winterkill.
- Sod extraction: This method involves farmers digging up several pieces of sod with a shovel. The pieces should be brought to room temperature while keeping the soil moist. After five to seven days, look at the crowns for new root growth, which indicates the plant has survived.
Remember that winter wheat plants need time to recover after our harsh prairie winters, so it’s important to scout the field as late as possible. New growth tends to be aided by cool, moist weather, so if conditions are warm and dry, stand establishment could be impacted and re-seeding may need to be considered.
Nitrogen fertility and protein management
In general, the MB Soil Fertility Guide recommends 80 to 120 pounds per acre of nitrogen to optimize yield potential without compromising on protein levels in winter wheat. Many farmers tend to apply most of their N fertilizer in the fall and apply the remainder in the spring, taking potential loss, stand assessments and fertilizer costs into consideration. It’s important to note that spring applications of N should be done early enough in the season to meet the crop’s early demand, as early N applications are important to stimulate tillering, especially if establishment was poor going into winter or winter injury occurred. In the case of winter wheat, the plants use 30 to 40 per cent N by the stem elongation stage (five to six leaf).
It is recommended that farmers protect against N loss from volatilization. Volatilization is the loss of N resulting from breakdown of urea into free ammonia (NH3) at the soil surface. Conditions that increase risk of volatilization loss include high temperatures, high soil pH, low rainfall, high surface residue levels, high winds and low soil organic matter. If no rain is in the forecast, use urea treated with a urease inhibitor (like NBPT), or dribble band UAN. UAN could also be treated with a urease inhibitor, but most of the loss protection comes from UAN form and placement. UAN or urea injection would avoid both volatilization and stranding, though few farmers have this option.
Winter wheat is very responsive to N fertilization. It’s important to remember that if soil N is low, an increase in yield can dilute protein content. A general rule of thumb is that if winter wheat protein is less than 11.5 per cent, the crop did not have enough N fertilizer to reach optimum yield potential.
Western Winter Wheat Initiative:
Manitoba Agronomists Conference:
- Evaluating Nitrogen Fertilizer Sources for Winter Wheat by Dr. Tom Jensen
- Winter Wheat – Breaking Through the Yield Ceiling by Ken Gross
Manitoba Agriculture - Winter Wheat Production & Management: