Timely and uniform emergence can help reduce soil erosion, minimize winter-kill, and particularly maximize yield potential by promoting fall production of tillers. Many factors determine when emergence occurs. Under normal conditions, emergence occurs about 7 to 14 days after planting (Table 2.2). However, emergence will be delayed if seeds are planted deep, the soil is extremely dry or cool, or crusting occurs. Farmers have several options for addressing seedbed soil water that is marginal or inadequate for uniform germination and seedling emergence. One option is to proceed with planting and hope for subsequent rains, but this is a risky strategy given the highly unpredictable weather in the Great Plains and low likelihood of timely rains in the fall. Another is to alter soil management practices to maintain soil water in the seedbed by minimizing soil disturbance and residue burial or removal. No-till systems can help retain seedbed moisture and promote good germination, reducing dependence on timely rains after planting. If only the surface soil is dry, deeper planting (into moist soil) may also improve germination, emergence, and survival.
Table 2.2 Average dates (dryland conditions) selected cultivars reached certain growth stages.
|Cultivar||Site||Sowing||Emerge||Start of tillering||Spring start||Jointing||Heading||Maturity|
|Centurk||Akron, CO||Sep 12||Sep 19||Oct 2||Mar 2||Apr 30||May 28||Jul 9|
|Centurk||Paxton, NE||Sep 18||Sep 26||Oct 6||Mar 14||Apr 30||Jun 4||Jul 7|
|Centurk||Garden City, KS||Sep 18||Sep 24||Oct 8||Mar 9||Apr 17||May 23||Jun 29|
|Scout 66||Albin, WY||Sep 6||Sep 15||Sep 28||Mar 23||May 7||Jun 12||Jul 17|
|Scout 66||Mankato, KS||Oct 2||Oct 9||Oct 20||Mar 10||May 18||Jun 14||Jul 16|
|TAM 101||Medford, OK||Sep 28||Oct 5||Oct 17||Mar 2||Apr 21||May 20||Jun 18|
|Larned||Tribune, KS||Sep 11||Sep 18||Sep 28||Mar 9||Apr 30||May 30||Jul 1|
|Prowers99||Akron, CO||Sep 26||NR||NR||NR||May 4||Jun 3||Jun 29|
Fort Collins, CO
|Oct 6||Oct 23||NR||NR||May 4||Jun 1||Jul 2|
|TAM 107||Akron, CO||Sep 26||NR||NR||NR||Apr 30||May 29||Jun 27|
|TAM 107||Fort Collins, CO||Sep 15||Sep 24||Oct 5||NR||May 8||May 27||Jul 9|
NR: Data not recorded for this site.
Leaf and tiller appearance are linked and start soon after emergence. Tillering usually begins about two weeks after emergence, if temperatures are adequate (Table 2.2). Leaves and tillers form at the growing point of each stem during the fall, winter, and early spring until the single ridge growing point growth stage, usually in March. The double ridge growing point growth stage signals the initiation of the wheat head and the shift towards reproductive growth stages. The double ridge stage is when spikelets are being initiated, which strongly influences the number of kernels per head. Fortunately, it is protected from low temperatures because it occurs while the growing point is underground. The double ridge growth stage is only visible under magnification, and occurs towards the end of tillering.
Spikelets and florets (i.e., flowers) form from the double ridge stage until booting. Booting marks the completion of the flag leaf, the major source of carbohydrates for grain filling. Different parts of the flower are initiated from booting until heading or flowering, which usually occurs in early June. Heading and flowering occur in very rapid succession. The maximum kernel number per head is determined during flowering. Subsequent stress-induced abortion may reduce kernel number per head slightly, but no additional kernels are formed after pollination. All yield components related to kernel number (i.e., number of plants, tillers, heads, spikelets, and florets/ kernels) have been determined by flowering. The final developmental stages relate to kernel growth, where yield is created. The last stage is maturity, the process of finalizing yield and drying of grain to harvest water content. Kernel size is set during this stage, with maximum size determined by mid-July.