Not long after Scott Johnson joined the UC Kearney Agricultural Research and Extension Center academic staff in the early 1980s, he began working with a brand new giant underground weighing lysimeter, an instrument that would become the signature tool of his career. Johnson retires June 30.

For more than a quarter century, Johnson conducted experiments with peach trees growing in the lysimeter, which allowed him to calculate precisely how much water evaporates from the soil and transpires from the tree on an hour-by-hour basis. Results of this research helped growers properly manage their irrigation strategies to improve fruit quality and yield.

A native of Utah, Johnson earned a bachelor's degree in biology at the University of Utah. He earned a Ph.D. at Cornell in 1982 and that year moved his family to the San Joaquin Valley to begin a 31-year stint as UC Cooperative Extension specialist in the Department of Pomology at UC Davis, based at the Kearney facility in Parlier, Calif.

Using the lysimeter, Johnson discovered that some common fruit tree irrigation strategies being used in the San Joaquin Valley were significantly impacting fruit quality and yield.

"We found that growers should not cut back on water after harvest, if they can help it," Johnson said. "Anytime we cut back on water applications, we developed some sort of problem – diseases, sunburn, mites and fruit disorders in the subsequent crops, like doubling and deep sutures."

Despite the importance of the irrigation research, Johnson had perhaps his greatest impact on growers' practices from his research on nitrogen fertilization. Many growers, he said, were over fertilizing their stone fruit orchards.

"We did a survey and found the average rate of nitrogen fertilization was 150 pounds per acre," Johnson said.

However, much of that fertilizer stimulated vegetative growth, which shaded the fruit and prevented the desired reddening; and required more pruning in the winter, labor that added to the expense of growing fruit. In addition, the high fertilizer rates caused more problems with fruit quality, insect pests and diseases.


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"I started working on this right at the beginning and harped on this same thing my whole career," Johnson said. "Today, farmers are using about a half or a third of the fertilizer they did decades ago."

Johnson also worked on understanding fruit trees' need for other nutrients, such as zinc and calcium.

"It was pretty common for growers to apply zinc every year," Johnson said. "From research we conducted at Kearney, we learned that orchards don't need zinc every year. We also compared materials and found the cheapest zinc products work just as well as expensive ones. We've saved growers a lot of money with these results."