The Basis of Canola Yields

Canola Yields

Canola plants convert the sun's energy into materials required for their growth by a process called photosynthesis. Canola crop yields ultimately depend on the ability of the plant to carry on photosynthesis. Photosynthesis must be maximized to achieve high yields. Factors that affect the rate of photosynthesis and ultimately crop yields, include:

  • available water
  • fertilizer practices
  • variety selection
  • seeding rates
  • seeding depths
  • weeds
  • pest control

Photosynthesis

Chlorophyll, a substance in green plant cells, is capable of absorbing sunlight energy and through a complex process converts this light energy into food materials for the plant. In photosynthesis, carbon dioxide (CO2) from the air plus water (H2O) from the soil are used by the chlorophyll of green cells in the presence of light energy to produce a carbohydrate or glucose sugar (C6H12O6) and release oxygen (O2) and water (H2O). In chemical symbols, the balanced photosynthetic equation is: Sunlight 6CO2 + 12H2O ---> C6H12O6 + 6O2 + 6H2O Energy

The plant uses the glucose in combination with nutrients from the soil for growth and development. Nutrients are essential for photosynthesis to occur. However, carbon dioxide is the main ingredient in the process. Over 90% of the plant's dry weight is composed of carbon dioxide products. Nutrients taken up from the soil account for the other 10%. Plants require nutrients for the synthesis of more complex products that make up the plant's body. These products are:

  • other sugars
  • proteins
  • fats and oils
  • cellulose
  • vitamins
  • organic compounds
  • lignin

Essential Plant Growth Factors

Plants depend on their environment to provide them with basic necessities for photosynthesis. These essential plant growth factors include:

  • light
  • heat
  • air
  • water
  • nutrients
  • physical support

If any one factor, or combination of factors, is in limited supply, plant growth will be adversely affected. The importance of each of the plant growth factors and the proper combination of these factors for normal plant growth is best described by the principle of limiting factors. This principle states: "The level of crop production can be no greater than that allowed by the most limiting of the essential plant growth factors." The principle of limiting factors can be compared to that of a barrel having staves of different lengths with each stave representing a plant growth factor (Figure 1).

Figure 1. Principle of Limiting Factors 

Fig.1

The barrel cannot hold anything above the height of the shortest stave (the most deficient or limiting factor). In other words, if most factors are ideal for crop production, yields will be held down by the one factor in least supply. A nutrient is the limiting factor in the illustrated barrel. Only by increasing the length of the shortest stave (adding the nutrient) can the 102 yield be raised to the full yield potential. If the plant growth factor in least supply cannot be controlled, for example, air temperature, it will limit the maximum yield.

Crop Production Factors

Canola yield and quality depend upon the essential growth factors and the many interrelated soil, plant, environmental and agronomic factors or variables. Within this system some of these factors cannot be controlled; others can be controlled and are manageable. Both production factors are shown in Figure 2.

Figure 2. Crop Production Factors

Fig.2

Consider production factors in light of their effect on photosynthesis. For example, any one or more of the plant growth factors moisture, nutrients, light, oxygen and carbon dioxide, which are essential for photosynthesis, may be in short supply at any time during development of the plant. A production factor like weeds will reduce the supply of these growth requirements. For example, weeds reduce light by shading or using up soil moisture, soil oxygen and nutrients that would otherwise be available to the crop. Control of weeds removes the limitations and photosynthetic efficiency is increased. However, weed control by tillage or herbicides may adversely affect other production factors.

Canola yield is the product of the components in Figure 3.

Figure 3. Yield Components of Canola 

Fig.3

Each canola yield component is greatly influenced by agronomic practices and the environment. Sunlight is rarely a limiting factor in obtaining high yields. Factors such as moisture, temperature, soil fertility, soil texture, soil structure, weeds, insects and diseases are usually responsible for a crop's inability to reach potential yield. For example, the number of plants per unit area is influenced by:

  • seeding rate
  • seeding depth
  • seeding date
  • fertilizer placement
  • seedbed moisture
  • seed treatment
  • variety
  • air temperature
  • seedbed soil temperature
  • soil texture
  • soil type
  • pH, tillage
  • soil surface residue cover
  • disease pressure
  • soil oxygen

All production factors are interdependent; if one factor is changed, many other factors can be affected. A positive interaction occurs when the growth response of two or more production factors used together is greater than the sum of their individual growth responses. There is an addon effect. Research has shown many positive interactions between production factors. In average-yield fields, these interactions still occur but at lower levels than in high-yield fields where they are very significant. Figure 4 illustrates that when production factors B, C and D are optimized and implemented, yields increase and larger quantities of fertilizer could be used more effectively.

Figure 4. Production Factor Interaction 

Fig.4

Crop production is a system in which all factors are integrated or brought together in balance with one another. An integrated system will be efficient, allowing for leastcost- per-unit canola production.

In most cases, yields are not likely to be increased by a single management factor. To achieve crop yield potential understand, recognize and remove the limitations of as many factors as possible. Do not become discouraged by the failure of a single change to increase yield but search out the factors limiting yield and modify them. It is frequently difficult to separate out the individual production factors as they are masked by the numerous positive interactions between fertility and other inputs or environmental factors. For example, yields may be successfully increased by greater use of fertilizer but only if:

  • the soil requires it
  • moisture is adequate
  • the crop is planted at optimum date, rate, depth and distribution
  • weeds are controlled
  • other production factors are favourable

An increase or modification in one input factor, which may appear to have a potential for increasing yields, without considering the other inputs, may not by itself result in an increase in yield. Frequently there will be a compromise between factors within the system. Direct seeding can produce better seedbed soil moisture but cooler soil temperatures may result. Using direct seeding can increase the seedling blight potential. Tillage may control weeds but can produce a drier seedbed which can reduce germination potential.

Recognize major limitations of soil and climatic factors and manage the factors that can be adjusted to increase crop yield. If all manageable crop production factors are at optimum, only the uncontrollable soil and climatic factors will limit yield.

Average Canola Yields

Average yields across western Canada vary somewhat due to differences in soil and climatic factors. Table 1 shows average yields in major canola production regions from 1990-2000. These average yields are low. In each of the regions, there are individual growers who, with the same soil and climate limitations as their neighbours, consistently achieve yields in the 2,200 to 2,800 kg/ha (40 to 50 bu/ac) range. Grower surveys have shown that canola yields are not limited so much by soil and climatic limitations as they are by failure to apply, modify and adapt crop production factors into an integrated system.

Table 1. Average Canola Yields by Area (1990-2000)
Region/Crop District Average Yield
kg/ha bu/ac
Manitoba      
Eastern 9,10,11 1,233 22.0
South-Western and Central 1,2,3,7,8 1,278 22.8
Western 4,5,6,12 1,295 23.1
Saskatchewan      
Eastern 1A,1B,5A,5B,8A 1,160 20.7
Central 2B,6A,6B,8B,9A 1,171 20.9
Western 7A,7B,9B 1,216 21.7
Alberta      
Southern 1,2,8 1,323 23.6
Northern 4A,4B,5 1,306 23.3
Peace Region 7 1,177 21.0
British Columbia      
Peace Region   964 17.2

Source: Statistics Canada

Individual growers have reported exceptional yields of 4,500 kg/ha (80 bu/ac). This indicates the potential yield increases that are possible when conditions are ideal. The growers who consistently obtain high yields pay careful attention to practices that will meet the crop's requirements for maximum photosynthesis at all its growth stages.

Summary

A high rate of photosynthesis is essential for consistently high yields. Photosynthesis is influenced by many crop production factors interacting within a system. The question growers must ask is "How can I maintain photosynthesis at the highest level through the proper combination of production factors?" A high yield can only be achieved when a proper combination of plant, soil, environmental and agronomic practices are obtained in the production system. Yields may be increased most efficiently if each input or each crop production practice is considered in light of how it works within a system and affects photosynthesis. A knowledge and ability to recognize and emphasize the positive production factors that increase photosynthesis will achieve high canola yields.

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