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This article in AJ

  1. Vol. 70 No. 6, p. 922-926



Alfalfa Winter Injury, Survival, and Vigor Determined from Aerial Photographs1

  1. V. R. Wallen and
  2. H. R. Jackson2



Some of the difficulties of assessing the physiological condition of an experimental plant population are the necessarily repetitive observations and the extensive time required to accomplish a thorough survey. Based on earlier work by the authors, a study was conducted to determine if aerial photographs of a plot of alfalfa (Medicago sativa L.) could provide information on plant survival and vigor, soil moisture, and the influence of soil drainage on winter injury beyond that obtainable solely from field observations. Aerial photographs were made over an alfalfa plot originally containing over 10,000 plants using black-and-white and color.infrared film. The photos were taken at 105 m with a 70 mm camera mounted on a helicopter. Visual assessments from the photographs made in the spring and fall of 1974 and in the spring of 1975 showed that from more than 6,000 surviving plants in 1974 only slightly more than 4,800 existed in the fall of that year; in the following spring, almost 400 more plants had not survived and from the total original population, 1,600 were rated as weak. Photointerpretation allowed an evaluation of plant vigor and the effect of soil drainage and high moisture on winter injury and survival. The study demonstrated that the use of aerial photographs, in addition to providing a permanent record of field conditions at a time selected by the plant breeder or pathologist, permitted large areas to be recorded and, because of their permanancy, increased the capability of reassessment.

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