ProCrop

Keys to Obtaining High Wheat Yields

The maximum wheat yield for a given year is going to depend on environment and management to coincide with the opportunities the environment brings. Wheat is a cool season plant and will yield better when the seasons are cool. 1985 and 1992 brought cool growing season weather and two of the highest yielding wheat seasons in North Dakota�s recent history. When the season is favorable for wheat, good management needs to accompany favorable weather.

Why do yields wheat vary from year to year?

Studies over the years have shown locations planted by the same operator can have wheat yields differing as much as 45 bushels per acre with the same variety. Even though these studies were planted at the same seeding rates with the same equipment, the same weed control, the same fertility program there is still wide variability in yield. There are many environmental and management reasons why this might occur. Rainfall patterns, soil type, previous rotations, inherent soil fertility and many other factors contribute to how a wheat variety may respond. The genetic potential of wheat is exceeds 200 bushels per acre. In many situations wheat fields at planting time using ordinary production practices in North Dakota have 100 bushel yield potentials.

Average Yields of Langdon Planting Rate Studies with Grandin HRS 1991-93.

What takes away from these yield potentials?

Stress due to environment or to management during the various stages of wheat growth remove yield potential one kernel at a time. The goal of the manager is to reduce the stresses and to preserve each kernel of yield potential. If wheat seed weighed 13,000 seeds per pound it would take around 78 million seeds to equal 100 bushels. When good management and environment come together good to excellent yields are obtained.

Wheat will adjust yield potential due to stress at various points throughout its life cycle. Wheat yield components are total heads per acre, number of spikelets per head, number of kernels per spikelet and the weight of the kernels developed. Total heads produced is the most important factor in producing high yields. Planting rate studies in northeast North Dakota and northern Minnesota have established that about 35 plants per square foot ( range of 26 to 41 plants) would be the optimal population for wheat in that environment . Obtaining a minimum of 26 plants per square foot will require a seeding rate that exceeds that number due to less than 100 percent germination and a 15 to 25% loss of seedlings in the emergence process. 26 plants per square foot would require seeding 1.5 to 1.6 million seeds per acre depending on seedbed quality and percent germination. Every seed lot varies in its seeds per pound and each producer needs to know the seed per pound of the seed lot in order to determine an adequate seeding rate.

The wheat plant can add additional heads per acre by initiating tillers at the 3-5 leaf stage and if favorable weather allows,1-2 tillers will survive to produce heads. If stress occurs between tiller initiation and heading, tillers are often lost and reduce yield potential. Additional opportunities for enhancing yield occurs at the 4-leaf stage to 5-leaf stage in wheat when head size is determined. Cooler weather at this stage generally results in larger heads with spikelet counts up to 16-18 per head being very favorable. Average head size over the years in ND is 12-14 spikelets.

A fourth opportunity for the wheat plant to adjust yields is at flowering when total number of kernels are determined . Five seeds can be formed in each spikelet of wheat. Generally, two to three are formed and in a good season four and occasionally five kernels are set in each spikelet. And finally after kernel set, seed weight is the final determinant of yield. Cool weather that favors a long filling period will allow wheat kernels to fill to their maximum amount and maximize yield potential.

Langdon Planting Rate Studies 1991-93 Affect of Seeding Rate on Grandin Yield Components. 16 sites

Stresses at any one of these stages can result in fewer heads per acre or smaller heads or fewer kernels or lighter kernels. If the environment is favorable, all that is needed is good management to continue to preserve the potential wheat yield that is there. Some of the key management decisions to obtaining and preserving high yields are crop rotation, securing a good seedbed, obtaining adequate plant population, having a good fertility program, using good seed of a correct variety, early planting to allow time for more development in the cool season and good pest control. High wheat yields often increases the potential for plant lodging. Choosing a strong strawed variety is a key to high yields as lodging will reduce yield and quality.

Rotation is probably the number one management key to assist in high yield production. Rotations with broadleaf crops and especially legume broadleaf crops often produce the best wheat yield as compared to planting on other grassy crops such as barley, oats or wheat. Good rotations allow for better pest management of weeds, insects and root diseases as well as provide enhanced residue management. Previous crop residues take two to three years to breakdown in North Dakota conditions. Thus if there is a severe disease infection present on residue, this disease will take a minimum of two cropping seasons to dissipate to low levels. A well planned and executed rotation will reduce many yield robbing pest populations and set the stage for maximum wheat yields.

Obtaining a good seedbed is critical to assist in management decisions in the 90 days that wheat grows. A good firm seedbed is needed to allow capillary action to continue wetting the seedbed to provide the best germination and emergence when rainfall is inadequate. Good seedbed management begins in the fall with residue management and tillage decisions that consider the quality of the spring seedbed. Good seedbeds provide the opportunity to seed at the correct depth of 1 � to 2 inches deep and increase the chances for uniform emergence of the crop. Good stands will increase uniformity of wheat growth which allows for better pesticide application timing.

Langdon Planting Rate Studies1991-93. 16 site ave. Effect of Seedbed Moisture on percent emergence

A comprehensive Fertility program is one of the important keys to producing high yielding wheat. Adequate phosphorus and nitrogen are essential for optimum yields.

Wheat planted into very low and low testing phosphorus situations responds well to seed row starter fertilizer of around 30 pounds of P²O per acre. Obtaining medium or higher levels of soil phosphorus would be desirable but often can be expensive. In medium or higher levels of soil phosphorus, placement is not as critical and wheat response to starter is less but can still be significant in cold spring soils.

Nitrogen management is critical to obtain high yields and good protein in wheat. A traditional approach of applying 2 � pounds of N per bushel of wheat either in the fall or spring preplant treatment is the norm in North Dakota. Most studies show that at yield levels up to 60 bushels per acre, fertilizing at 125-150 pounds per acre preplant will be as good as other application methods. Leaching or de-nitrification of nitrogen may require supplemental nitrogen applications.

Effects of Post applied dry ammonium nitrate to 4-5 leaf wheat in Western and Northwest Minnesota. Early 1990�s. Lamb and Rehm. Source: Minnesota Crop News May 14, 2002. Wiersma et al.

For further information see http://www.plpa.agri.umn.edu/extension/news%20releases/mncn63.htm
For further information see http://www.ag.ndsu.nodak.edu/aginfo/procrop/fer/topdressing.htm

Split applications of nitrogen offer the grower a chance to respond to high yield potentials without applying large quantities of preplant nitrogen. A yield goal of 80 bushels per acre requires a total nitrogen need of around 200 lbs per acre. Large nitrogen amounts for high yields can increase plant lodging. Some studies have shown reduced lodging or a tendency to reduce lodging when nitrogen is split applied as compared to all nitrogen applied preplant. Very little data is available at 80 bushel yield levels as these yield levels are seldom reached in ND conditions.

Split applications of Nitrogen with additional amounts of N being applied post emergence for high yield situations are dependent on the nitrogen fertilizer being incorporated adequately, generally by rainfall or irrigation into the soil for absorption by the roots. Studies have shown that when soil nitrogen levels are adequate for average yields, application after the 5-leaf stage generally contributes to protein rather than to wheat yields. The wheat plant requires about 25 pounds of N until canopy closure at about 5-leaf stage. From the 5^th leaf stage to heading, 60-70 pounds of N are taken up by the plant or two to three pounds of nitrogen per acre per day. This is a tremendous need by the plant and deficiencies at this time will create stresses that reduce yield potential. When supplementing nitrogen, be sure that the post application of nitrogen is applied early enough to be incorporated by a timely rain so that the plant is not deficient at any stage. If higher seed protein is needed, numerous studies have shown that post anthesis foliar nitrogen application, when protein premiums warrant the expense, will increase wheat protein two-tenths to one-half percent.

Pest management of course is also an essential when pests are present and cause stress and reduce yields. When pest levels warrant, fungicides, herbicides, and insecticides have all been shown to be keys to good quality and high yields. Pest problems vary over the years and require close scrutiny and management decisions need to correspond with the severity of the problem. Varietal resistance when available should be used to prevent stresses to pests.

In summary, wheat has the potential to yield 70-80 bu /acre in North Dakota if environment and the management coincide. If either are lacking, average yields are the result. Paying attention to details, having good timely rains and generally cooler weather will produce the maximum wheat yields for that year.

Author: Terry Gregoire

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