Grain Growing Classroom

The Importance of Your Optimal Planting Window

We want to avoid the probability o higher temperatures during spikelet formation

By Jochum Wiersma
U of M Small Grains Specialist
wiers002@umn.edu

With the 2005 growing season underway, it’s worthwhile to review a few fundamentals related to small grains planting.

Planting date – Planting should be done as soon as a good seedbed can be made. General guidelines for the optimum planting window are given in the table below.  Research across the region has shown that, on average, yields decrease 1% per day when planting is delayed past the optimum planting date (Figure 1). In northern Minnesota, this decline in yield usually occurs after the first week in May and in the southern part after mid April. At a 50 bushel/acre yield goal, this is one-half bushel per day.

The main factor contributing to yield reduction due to delayed seeding is the probability of higher temperatures.  Higher temperatures will speed up the development of the plant.  This will reduce the number of tiller initiated and the number of spikelets per spike formed (Figures 2 and 3).

Whenever maximum day temperatures reach above 63 degrees during this specific growth stage, the number of spikelets per spike decreases.

Planting rate – Seeding rate is a function of the number of kernels per pound of seed, percent germination of the lot, expected stand loss, and desired stand. An average optimum stand of spring wheat when planted early is generally between 30 to 28 plants per square foot or about 1.30 – 1.40 million plants per acre. This number should increase by one to two plants per square foot for every week planting is delayed past the optimum seeding date. Keep in mind that expected stand loss even under good seedbed conditions is 10%-20%, and will increase with a poor seedbed or seed placement.

Planting depth – Rule of thumb for seeding depth in small grains is 1.5 to 2 inches. Our objective is to get the seed in a zone with ample moisture but shallow enough that the crop can emerge quickly. Cooler soil temperature at deeper depths increases emergence time.

Replanting – If stands are not optimum, wheat can partially compensate. However, when do you decide to replant a stand? Assume you wanted a stand of 1.3 million plants per acre. That requires at least 30 plants per square foot. Consider that replanting costs must be recovered from a later maturing crop that has a lower yield potential than the original crop. Plus, replanting uses extra moisture as a function of soil disturbance.

Use the following guidelines to determine whether replanting is worthwhile:

1) If reduced stand is uniform (no big skips or holes) keep stands at 15 plants per square foot.

2) If skips are large (3 to 6 ft), or holes are 4 to 6 feet in diameter and stand is 18 plants per square foot or less, then replant if moisture is adequate.

3) After June 1 in northern Minnesota, and May 15 in southern Minnesota, a replant decision should be to a crop other than wheat or barley since yields are reduced about 50% when planting after these dates compared to normal planting dates.

Thus, stands as low as 15 plants/sq ft, if uniform, should probably be left alone, because the chances for you to improve the yield potential by reseeding are probably not in your favor. Strive for an optimum stand, but realize that less than optimum doesn’t necessarily spell disaster, because of the wheat crop’s remarkable ability to compensate with tillering.  

Minnesota	North Dakota	Optimum	Last Planting Date
South of U.S. Hwy. 12	Not Applicable	1st week of April	1st week of May
South of MN Hwy. 210	South of Hwy 13 and 21	2nd week of April	2nd week of May
South of U.S. Hwy. 10	South of I-94	3rd week of April	3rd week of May
South of U.S. Hwy. 2	South of U.S. Hwy. 2	4th week of April	4th week of May
South of Canadian Border	South of Canadian Border	1st week of May	1st week of June