How Does Crop Canopy Structure Affect Yield? 5 Key Factors Explained

• Crop canopy attributes influencing yield are leaf area, inclination angle, ground cover fraction, and chlorophyll content.
• The attribute that could increase yield by optimizing photosynthetic efficiency, light interception, water use efficiency, or reducing weeds, stress, and disease can vary on the relevant crop physiology.
• Increasing emphasis on crop canopy attributes can maintain and increase yield by estimating existing cultivars for canopy ideotypes.

Crop canopy structure is usually associated with increasing photosynthetic area, but it can also influence the use of resources and plant stress due to pests, diseases, and weeds. Often, plant breeding programs focusing on improving yield have not considered the various influences crop canopy can have, so cultivars can have canopies that are optimal only for photosynthetic efficiency. Optimizing yield is not always synonymous with more cover since biomass accumulation isn’t determined only by carbon assimilation. Find out more on how crop canopy structure’s importance throughout the crop cycle can influence yield.

Crop Canopy Structure

Figure 1: “Overview of features affecting plant architecture. The phenotype is determined by genetics and local environmental conditions” Murcie and Burgess, 2022. (Image credits: https://doi.org/10.1016/j.crope.2022.03.009)

Crop canopy structure is a critical component of yield. The leaves arrangement in three-dimensional space determines the amount of light intercepted by the entire plant and its microclimate to influence plant productivity.

The vital canopy structure attributes to be considered for improving yield are as follows:

• Canopy architecture
• Leaf angle
• Leaf morphology
• Chlorophyll content
• Ground cover fraction

Crop canopy structure is determined by the plant type, genetics, and environmental interactions (see Figure 1). Plant types determine the primary structure, for example, in monocotyledonous plants/grass (cereal), dicotyledonous plants (legumes, vegetables, etc.), or trees (fruits like mango or apple).

There are differences in crop canopy between cultivars (See Figure 2), which can be used to optimize yield in different growing conditions, considering all the canopy functions.

The plant functions that crop canopy influences are:

1. Photosynthetic efficiency
2. Light interception
3. Weed suppression
4. Disease incidence
5. Stress moderation

Figure 2: Schematic diagram of the different canopies of four cotton cultivars, Feng et al. 2016. (Image credit: https://www.sciencedirect.com/science/article/pii/S2214514116300988)

1. Photosynthesis Efficiency

The essential factor that crop canopy influences is photosynthetic efficiency. Leaf area, chlorophyll content, and ground cover fraction determine the amount of photosynthesis that occurs in a plant.

The precise crop canopy attribute that is influential varies according to biomass. In plants with less canopy, the available leaf area affected photosynthesis. As leaf area increases, photosynthesis increases up to a point. In plants with higher canopy biomass, there is more photosynthesis when the top canopy allows more light to reach the lower canopy for carbon assimilation. Canopy attributes other than cover fraction become essential to optimize whole plant photosynthesis.

In a recent study on soybeans, leaf photosynthesis explained only 15 percent of the variance, and all crop canopy attributes explained 40 percent of the variance in photosynthesis.

Photosynthetic efficiency in a plant determines carbon assimilation and yield in a crop, regardless of the species and plant type, so increasing it is the aim of all research.

2. Light Interception

Plant light interception depends on plant attributes and the angle of solar radiation. Light intercepted is mainly direct light; the rest is diffused and transmitted light remitted by objects. Under full sunlight, 85 percent of the light interception is direct light. Diffuse light fraction increases when the sun is at the horizon. Besides the sun’s position, length of daylight, latitude, wind, season, and cloud cover are the environmental factors determining light falling on a plant.

The leaf area and inclination angle influence whole-plant light interception. Erect leaves have less light interception in direct light but more in diffuse light. However, upright leaves or upper leaves with less chlorophyll reduce shading and allow more light interception deeper into a canopy and the ground, changing the microclimate. The light progressively decreases towards the ground and is often available only as sun flecks at the bottom.

Preventing light saturation in the upper canopy and light limitation in the lower canopy is vital to increase biomass and yield. The ideal plant type or ideotype for cereals focuses on erect leaf morphology. It leads to an increase in whole plant leaf area and has been found to increase yield in hybrid rice and wheat. For soybeans, the ideotype would be light-colored leaves with less chlorophyll in the upper canopy and darker leaves with more chlorophyll in the lower canopy.

The ability of plants to benefit from increased light interception and sun flecks in the lower canopy depends on leaf age, lower plant height, and availability of nutrients.

The change in microclimate has several other consequences on yield, discussed separately in the following sections.

3. Stress Reduction

Shading by the upper canopy influences the temperature and humidity in the lower canopy, affecting the amount of photosynthesis and other physiologies throughout the crop cycle.

The lower canopy has lower temperatures and more humidity due to shading by an upper canopy. The soil temperatures are also lowered by shading. This is true even in ideotypes, allowing more light interception. As a result, there is more photosynthesis due to lower photoinhibition, excessive light, and overheating. Increasing humidity also reduces water use and increases carbon assimilation and yield.

Figure 3: Panicles in new rice varieties are surrounded by plant canopy and

benefit from transpiration cooling, Wassmann et al. (2009). (Image credits: ISBN: 978-0-12-374817-1)

Crop canopy that reduces soil temperature is crucial for crops like late-planted potatoes since higher soil temperatures significantly reduce root growth and tuber formation.

Later in the crop season, cooling transpiration can be advantageous during sensitive anthesis stages. High temperatures result in sterility by affecting another dehiscence, pollination, or fertilization, depending on exposure duration. For example, in rice, semidwarf hybrids with compact canopy have panicles surrounded by leaves, which lower canopy temperatures, allowing the cultivars to avoid heat effects. Such heat-avoiding cultivars achieved by improving crop canopy can be crucial for climate-proofing and maintaining yield in hot tropics.

Plants can be prone to lodging if they are tall. Shorter plants can reduce lodging risks in cereals legumes like peas, soybeans, etc., and increase standing plant density and yield.

When photosynthetic efficiency increases due to using ideotypes that maximize carbon assimilation and minimize water loss, water use efficiency increases. Crop water efficiency refers to carbon assimilated for every unit of water lost by the canopy. This feature will also become valuable in planning for climate change, where water availability is expected to drop.

4. Weed Suppression

Another impact of microclimate change on the ground by crop canopy shading is the reduction of weeds. Globally, 34 percent of yield is lost due to competition by weeds. Since weeds are resistant to 23 of 26 widely used herbicides, they pose a risk to food sustainability. Moreover, the additional use of herbicides is increasing farming costs. Reducing weeds through crop canopy is becoming an attractive proposition.

Fast early growth and establishment of crop canopy can reduce competition from weeds. Shading reduces weed germination and development to improve crop establishment and reduces the loss of nutrients and water added to the fields. Moreover, selecting canopy cover that can suppress weeds along with closer rows can reduce the herbicides that need to be added to a field.

The canopy attributes that enhance weed suppression abilities are crop height, leaf inclination angle, and higher leaf area. Earlier hybrids with compact canopy and shorter height were less vigorous, making them prone to weeds. By including selection for canopy attributes, scientists have identified cultivars in the existing semidwarf varieties that are also more vigorous growers and can suppress weeds.

Competitive wheat varieties have reduced weed growth and herbicide application by 50 percent and improved yield and ROI.

5. Disease Control

While reducing plant spacing is suitable for controlling weeds, it spreads disease infection. Choosing a crop canopy that creates a microclimate unfavorable for diseases can help to reduce their incidence and spread. Crop canopy improvements have led to less fungicide use and expense and more fungicide efficacy. An ideal crop canopy can help decrease the 10-23 percent yield loss due to fungal infections despite fungicide use worldwide.

In most cases, the suitable ideotype to control diseases has a crop canopy that promotes more air circulation, more light interception, and fast leaf drying to reduce wetness duration in the microclimate, as detailed below.

• Fewer leaves, less leaf area, upright determinate stems, or short plants with few main stems and side branches reduced diseases in beans.
• A crop canopy with less Leaf Area Index and long internodes reduced blight in peas.
• Lateral trimming to curtail canopy in carrots by 30-40 percent limited sclerotinia rot without using chemicals.
• Soybeans with less height and early maturity suffered 74 percent less sclerotinia rot and an overall 88 percent reduction of disease during harvest.

However, in some cases, more crop canopy is needed for disease control, so the modifications need to be species and pathogen-specific. For example, rapid early growth of canopy in potatoes that covers the soils is required to reduce raindrop splash and blight.

Measuring Crop Canopy

The various studies show that though broad trends exist to optimize the crop canopy, the ideotype needs to consider species, local growing conditions, and pathogen systems. To develop an improved crop canopy, breeding new cultivars or selecting from existing varieties, using precise measurements of the crop canopy will be required. Here, portable, accurate instruments like CID Bio-Science Inc.’s CI-110 Plant Canopy Imager, which estimates canopy attributes in real time, are valuable. The canopy imager estimates Leaf Area Index, ground fraction cover, PAR, and sun flecks. Evaluating cultivars with the CI-110 Plant Canopy Imager to find suitable crop canopies from existing genotypes can quickly optimize yield and stress response to increase food sustainability.

Sources

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