Making Up Lost Ground (actually, for Lost Plants or Leaves)

Reviewing the condition of various farm fields and research plots prompted me to revisit the process or phenomenon of yield compensation (also mentioned in VegNet June 30). Recently, I saw fields and plots showing missing plants and plants with leaves damaged by insect feeding, mechanical damage, and other causes.

For each crop, there is a plant population shown by research and/or experience to maximize yield potential under specific combinations of variety, planting date, irrigation and fertility program, and other factors. Similarly, yield potential is known to be greatest within target ranges of leaf area index (LAI). LAI is calculated as half the area of all leaves per unit area of ground. It is measured as the leaf area (e.g., square feet) per ground area (square feet) and unit-less. So, a plant, field, farm, or region with a LAI of 3 has enough leaf surface (one-sided) to cover an area three times larger than the area from which the leaves were collected. To calculate LAI, most researchers collect all leaves from above a known area of ground, scan the leaves to calculate their total area, then divide that area by the area from which the leaves were collected. Techniques involving cameras and smartphones are improving the opportunity for obtaining estimates of LAI in the field without removing leaves. Regardless, LAI values have long been used in different ways in agriculture, forestry, climatology, ecology, and other disciplines and industries.

Overall, yield compensation asks if yield will be reduced if plant populations or LAI values are less than the target. The answer is easy for some crops such as fresh market sweet corn; “yes”, since one less plant results in one less ear available for harvest. The answer is more complicated (and encouraging) for other crops able to “compensate” for a reduction in plant population and/or leaf area (LAI) under specific circumstances.

This picture taken at OARDC shows a young butternut squash planting. Based on in-row plant spacing, the image should contain thirty-four plants. However, four plants (12%) are missing outright and four others are noticeably weaker than all remaining ones. So, the absolute percent stand is 88% but, functionally, it may be as low as 76%. Will this planting have a yield equivalent to the yield at 100% of the target population? That is, will the remaining plants compensate for missing ones?

Work completed in 1998 and 1999 by a team of extension specialists in NY and PA gives some clues. Dr. Anu Rangarajan and her collaborators studied defoliation and plant loss effects on butternut squash yield (fruit number, size, and weight) and other variables. Stands ranging from 25 to 100 percent of target populations were created at different stages of growth. Likewise, stands were defoliated to simulate damage due to insect feeding, hail, or other issues. The team summarized its work in the July-September 2003 issue of the journal HortTechnology. Borrowing from that report, the team stated that reducing plant populations or leaf area reduced marketable yield, fruit number, and individual plant productivity (but not fruit carotene content). Damage occurring during fruit enlargement had a greater effect than damage occurring early in the season. Generally, yield was directly proportional to plant population. However, if plant population losses occurred when plants were in the rapid vegetative growth phase, remaining plants responded by increasing fruit number and weight per plant. Still, this compensation did not always provide yields equivalent to the original population. The authors concluded by saying that for growers trying to assess the impact of plant loss or damage, butternut squash compensated for loss of up to 50% of plant population and up to 33% loss of leaves, particularly if loss/damage occurred early in the season.

The take-home message for the planting pictured here and many others? Compensation may save the day. Let’s hope conditions hold steady or improve and that our plantings’ abilities to compensate are not tested further.

Information regarding the article referenced above:
Title: Moderate Defoliation and Plant Population Losses did not Reduce Yield or Quality of Butternut Squash
Authors: Anusuya (Anu) Rangarajan (Cornell Univ.), Betsy A. Ingall (Cornell Univ.), Michael D. Orzolek (Penn State Univ.), and Lewis Otjen (Penn State Univ.).
Source: HortTechnology July-September 2003, 13(3):463-468 (https://journals.ashs.org/horttech/view/journals/horttech/13/3/article-p463.xml)

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