In October, we find ourselves in the thick of planting season, yet at this point in the month, there are some fields that have not been planted, some that are just newly sown, and some populated already with seedlings. There is much activity in our fields—both above ground and below. Amidst all this activity from our plants, we have many decisions to make, and replant decisions rank high among them.
Wheat seeds start the germination process by absorbing water and oxygen. The germ of the wheat (embryo) gives rise to the seedling root (radicle) and the first leaf, while the second leaf (coleoptile) pushes upwards through the soil. If conditions are favorable with enough moisture and temperatures are between 54 and 77 degrees, emergence will take place in just 5-7 days after the seed is put into the ground.
Above ground, photosynthesis—the process by which plants convert carbon dioxide, water, and energy from the sun into sugars and starches—begins in in the leaves of the plant. Photosynthesis produces not only the foliage on wheat plants, but the grain as well.
Tillers production starts shortly after emergence. Normal growing conditions produce plants with 3-6 tillers, though the actual number of tillers produced is determined by a combination of factors including soil moisture and fertility, variety, seeding rate, and temperature.
Below ground, secondary roots, (or crown roots) emerge from nodes to create the root system. Though most roots occupy the top six inches of soil, some penetrate as far as seven feet. The growing point, which consists of nodes, internodes, and the head, remains below ground until spring greenup, at which point jointing occurs and the growing point moves above the soil surface.
Once our wheat plants are up and growing, we are put to the important task of evaluating our stand. You can get a good idea of the quality of your stand by its mere appearance, but taking the extra time to calculate your total emergence will give you a solid number on which to judge your success and on which to base future decisions. In order to maximize grain yield, you need between 700 and 1000 heads/ square yard at harvest. Wheat sown at 2 bushel/acre will generally result in about 350 seeds/ square yard, meaning that we will need at least three tillers per seed that go on to make a wheat head.
1-1.5 million seeds per acre are common rates planted in the eastern part of Kansas. To determine your total emergence, simply use a yardstick or a tape to measure out three feet of an average looking row. Counts the plants in that three foot row and repeat this procedure in four other locations in your field. Determine the average of those five counts and plug that average into this equation:
Plants/sq ft=(average plant count x 4)/ row width in inches
Once you know your plants/sq ft, consult the table below to determine your final stand percentage.
If your final stand percentage is 50% or better, the general rule of thumb is to keep the stand. If your percentage is less than 40%, the general rule of thumb is to replant. Percentages falling between 40% and 50% fall into a gray area and the decision to replant becomes harder.
In cases of stands between 40% and 50%, considering other factors such as plant health, weather, soil conditions, and variety can assist you in making your decision. The detriments of a thin stand on your field are worth considering as thin stands allow easier wind erosion and weed infestations since there are fewer wheat plants holding your soil in place and crowding out unwanted weeds—both factors that can cause unwanted yield loss.
A stand of 270-360 plants/ square yard (30-40 plants/square foot) is a target population. The decision to replant is best made after a careful stand count and evaluation of your field. This can be a painful decision to make, so if you find yourself uncertain or in need of further information, please contact your local crop consultant or FSA with questions.