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Source-Sink Relationship in Crops

Categories: GROWING, CORN

Yield potential is influenced by the source-sink relationship within the crop plant and is the cumulative result of the strength of both the source and the sink. The source is photosynthates produced from the vegetative portion of the plant through photosynthesis. Grain is the sink, where photosynthates and nutrients are mobilized in the plant. Essentially, plants need deep green leaves that capture high levels of light and have the ability to move the sugars created by photosynthesis into the grain.

This relationship is important in both corn and soybeans. Over the last 50 years, increases in yield potential have been generally achieved through increased partitioning of biomass into the grain, increased responses to nitrogen fertilizers, and increased canopy development (allowing for increased light interception).1 Even though elements of grain yield are set for corn earlier in the growing season, the plant will still need to harvest sunlight through the leaves until maturity in order to fill the kernels.

Factors that Reduce the Source Strength
Any type of stress on the leaves of the plant will reduce the strength of the source functions. For example, anything that drastically reduces the green material or leaves will reduce the source capacity of the plant. Some common plant stresses that influence the source include:

  • Disease – lesions from various diseases reduce the green material of the leaves, ultimately reducing the amount of light harvested and photosynthetic capacity.
  • Drought – rolled leaves have less surface area to capture light.
  • Nutrient stress – deep green colored leaves contain more chlorophyll (the “factories” that capture light and create energy for the plant). Pale, yellow, or chlorotic leaves are much less efficient at driving photosynthesis.
  • Insect feeding – removal and skeletonization of the physical leaf material.

Testing the Source-Sink Relationship in Corn
Golden Harvest implemented a small trial in WI to test altering the source of corn. The goal of this trial was to see if there is a portion of the leaf canopy (source) that correlates more to the remobilization of photosynthates into the ear (sink). There is discussion every year around tasseling of protecting the ear leaf and upper canopy of corn when foliar fungicide application decisions are usually made. To test canopy importance on grain fill, 5 leaf removal treatments, each 4 rows wide and 10’ long, were applied near the R2-R3 growth stage.

Ear images and weights were taken from each treatment plot to estimate yield.

​​​​​​It is important to remember that this trial was a very small-scale test in only 1 year, so the amount of data is limited, and the yield may appear to be high for the area. The results do show a yield trend from the leaf removal treatments.

The data from this trial supports the recommendation of protecting the ear leaf and upper canopy. It is important to protect the upper canopy leaf biomass from diseases. Maintaining the large ear leaf and upper canopy leaves helps to capture the most light available when the plant is working to fill grain. These later growth stages are when the corn plant will pack in sugars, test weight and develop deeper kernels. If the entire canopy can be protected, the crop may be able to gain extra bushels and punch through a yield ceiling.

The best corn hybrids are able to finish the growing season strong and have some of the following characteristics and management:

  • Stay-green
  • Disease tolerance
  • Fertility management
  • Adequate water
  • Fungicide management

Obviously, getting a good start in the season is a great lead, but it is critical to think about how to support the crop in later season stages. Connect with your local Golden Harvest Seed Advisor with questions around late season management strategies.

Photos are either the property of Syngenta or used under agreement.
Syngenta hereby disclaims liability for third-party websites.


1 Long, S. P., X.-G. Zhu, S.L. Naidu, and D.R. Ort. 2006. Can improvement in photosynthesis increase crop yields? Plant Cell Environ. 29: 315–330.


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