Agriculture

Aiming for Higher Wheat Yields

There is often one common theme that each farmer refers to in their ‘recipe for success’ that farmers here in Manitoba can use on their own farms. It is optimizing plant populations and often pushing the population beyond what many may consider ‘normal’. There will be debates about this as there are many yield enhancing and of course yield limiting factors that come into play each season. However, some would argue that there is only one opportunity to set the crop up for success. Plant populations have to be optimized from the very start as there is no increasing the number of plants out in the field once the crop is up and growing.
 
THE REWARDS OF INCREASING PLANT POPULATIONS: INCREASED YIELDS & UNIFORMITY

Perhaps the biggest reward or advantage to increasing plant populations is increased yield potential. Remember - plant population affects yield by influencing all three of the primary yield determinants: number of heads per acre, number of kernels per head, and the weight per kernel. Higher plant populations also mean greater light interception (more photosynthetic area) and lower weed competition.

Another benefit of higher plant populations is the increase in stand uniformity. Heavier plant stand densities result in a fewer number of tillers. A reduction in the number of tillers can result in uniform flowering and maturity which will hopefully translate into improved yields, improved kernel uniformity, and quality.
 
In areas where wheat midge and fusarium head blight (FHB) are concerns, if the crop flowers or heads out uniformly farmers can better manage fungicide and insecticide applications. Particularly with FHB products, timing is absolutely critical for product effectiveness. Also consider a more uniform stand can result in more uniform maturity which can make operations such as swathing or straight cut harvesting much easier. And yet one more point to consider is the higher number of tillers seen under lower populations will delay maturity which may increase risk of a fall frost impacting both yield and quality.
 
THE RISKS OF INCREASING PLANT POPULATIONS: INCREASED LODGING & COMPETITION

One of the risks associated with higher plant populations is the increased potential for lodging which can impact yield and quality. This may be particularly true under high yield environments like the Red River Valley. When using higher seeding rates, growers are advised to select semi-dwarf and shorter-straw varieties or varieties with very strong straw strength. Seed Manitoba is an excellent source to assist with selecting varieties. It is available online at the following link: http://www.seedmb.ca/ or at local GO Offices. It would also be good to talk with seed growers and representatives to ensure the variety you’re growing will respond under high populations.
 
Another consideration of higher plant stands is a thicker canopy which may lead to higher disease pressure. Scouting will be important during the season to monitor disease pressure in case fungicide applications are warranted.
 
Increased plant density can also place plants under more stress through inter-plant competition for nutrients, light, and moisture, particularly if any of these factors are limiting. The result can impact any of the three yield components potentially leading to a reduction in yield and quality.
 
CALCULATING SEEDING RATES

You have made the decision to increase plant populations to realize some of the rewards. The next step is to calculate seeding rates (which refers to the number of wheat seeds planted per acre) needed to obtain the desired final plant populations (the number of wheat plants per acre that will produce yield). To accomplish this goal of achieving higher plant stand densities the number one rule to follow is DO NOT SEED BY BUSHELS PER ACRE!  To help ensure success, there are three critical pieces of information farmers need to determine: target plant stand, 1000 kernel weight and expected seed survival, which includes % germination. Using this information in the equation below will determine the most accurate seeding rate to achieve the desired plant stand.
 
 
Seeding Rate  (lb/acre) =
target plant stand per ft2 x 1000 kernel weight in grams
% expected seedling survival* x 10
 
* Expected seedling survival is used in its decimal form (90 per cent = 0.9).
 
1. TARGET PLANT STAND PER SQUARE FOOT
The optimum plant population for a field is determined by many factors, including crop management practices and growing conditions. Every field may not have the same target plant stand. Current recommendations to optimize spring wheat yield potential indicate target plant populations should range from 23 to 28 plants per square foot. However, many farmers are pushing these limits and targeting up to 30 plants/ft2 and in some cases up to 35 plants/ft2.
 
Factors to consider when targeting higher plant stands include:
 
  • Variety – semi-dwarf and shorter-straw varieties or varieties with very strong straw strength
  • Seeding date – when seeding is delayed in order to shorten the time to maturity
  • Field selection - fertile, well-drained fields with good moisture holding capacity 
  • Growing conditions - ensure conditions in your area can handle an increase in plant population. Evaluate soil moisture, temperature, potential pest issues (disease)
  • Management practices - need to ensure the crop is managed to handle the increase in plant population. Examine fertility program, pest (weeds, diseases, insects) control measures.
  • Economics - consider the economic return of planting more seed.


Because there are numerous factors that come into play when determining target plant stands, it may take a few growing seasons to fine-tune target plant stands and determine just how far they can be pushed in a grower’s system. 

 

2. 1000 KERNEL WEIGHT (TKW)
The 1000 kernel weight can be measured simply by counting out 1000 seeds of grain and obtaining the weight in grams. Seed weights vary between varieties, fields and from year to year. Remember that every lot of seed and variety are not the same - just because your KANE wheat was 38 grams last year does not mean that it will be the same this year. It is important to get those results either through your seed dealer or testing of farm-saved seed every year as it will influence how much seed you need to order or save for seeding.

 

3. EXPECTED SEEDLING SURVIVAL
Expected seedling survival is the expected germination less a small amount for seedling mortality. In the formula, expected seedling survival is expressed in decimal form, i.e. 0.9 should be used for 90%.
 
% GERMINATION
The ability of the seed to germinate is critical. A seed is a living organism and can change from the time it’s taken off the field to planting. Hence, testing for germination only once a year may not be sufficient. Repeating a germination test a few times throughout the winter season is also good practice if a high percentage of abnormal or dormant seeds are found. Make sure to ask your seed dealer for the test results. If considering using farm-saved seed, also be sure to test – and make sure a test is done after seed cleaning. Since most germination tests are relatively inexpensive, it is a small price to pay to ensure seed does have planting potential.
 
Reports from seed testing laboratories are confirming what many already suspected – that in some cases the less than ideal 2010 growing season (poor harvesting conditions, frost, disease pressure, delayed maturity) has resulted in seed with below average germination and higher than average levels of disease. If your seed lot does have lower than ideal germination, this of course will translate into higher seeding rates.
 
SEEDLING MORTALITY
When determining seeding rates, be sure to take into account the seedling mortality rate, i.e. what percent of viable seed will not produce a plant. Under normal conditions many farmers and agronomists have found a 5 to 10% mortality rate can be assumed. However, farmers need to consider with the wet conditions and late harvest in 2010, many fields were not worked prior to freeze-up or the first snowfall. Going into 2011 farmers will likely see challenging conditions during seeding including wet, cold soils and heavy residue which can impact the seeding operation. Under these types of conditions assume higher mortality rates (15 to 20%) when calculating seeding rates.
 
A FEW OTHER CONSIDERATIONS
The benefit of increasing plant populations can be quickly wiped out if consideration isn’t given to the entire seeding operation.
 
  • Selecting quality seed can reduce the risk of poor stand establishment as well as a crop’s ability to compete with weeds, diseases, and insects during the growing season. Regardless of the reasons, poor quality seed should not be used except in extreme shortages of good quality seed. Planting poor quality seed will result in seedlings, if they do emerge, being weaker and less able to withstand poor spring growing conditions such as drought or frost.
  • If disease is a concern, seed treatments can protect germinating seed and young seedlings from seed-borne and soil-borne pathogens. Although certified seed guarantees quality and variety purity, it does not guarantee freedom from seed-borne disease. Test seed at an accredited lab if there are concerns. If considering using farm-saved seed, test after cleaning the seed. Keep in mind that seed treatments do not bring dead seeds back to life but can help seed lots with disease pressure.
  • Pre-planting management factors to check include seed bed preparations such as even distribution of residue and ensuring field is not too rough.
  • During seeding, also ensure your speed is suitable for the field conditions. If field conditions are poor and you are planting at a higher speed, the planter bounce can cause seed depth misplacement therefore affecting uniformity of emergence – likely one of the rewards you were hoping for when increasing plant populations.
    Well before the start of the seeding season is the time to fine tune and calibrate your seeder based on your calculated seeding rates – not as you’re pulling into the field when the time crunch is on. 
  • Planting when soils are too wet is not advised, regardless of the date or what populations you’re targeting. Yield reductions resulting from "mudding seed in" are often greater than waiting a day or two for the soil to be ready.
  • After the seeding operation is complete, field scouting once the crop is up and growing will help to determine if the producer hit their target plant stand or missed the mark. The easiest method to measure plant stand is divide 144 (the number of inches in a square row) by the row width in inches. The answer is the number of inches of each row you need to count plants in to equal a square foot. For example, in 8 inch rows, 144/8 = 18 inches. If you count the number of plants in 18 inches of row, you then know the stand per square foot. And of course, counts should be taken in many areas of the field to get an accurate assessment of plant stand. If you hit the target population, this part of the seeding operation is going well. If not, note the factors that influenced final plant stands for future improvements. Also check if the wheat plants are all at the same leaf stage. If there are plants that are one to two leaves behind their neighbors, it could indicate potential problems that can be addressed in the future.