This experiment was initiated because Jonagold quality was diminishing in many orchards. The symptoms matched those of a potassium deficiency in several locations, dull green fruit color with insipid taste. Jonagold appears to be a high user of both potassium and magnesium, suggested by the fact that adjacent varieties didn't show symptoms as fast.
Soil analysis shows that drip irrigation leads to a drop in potassium levels.
At this time the fruit is also sizing rapidly and demand for potassium is particularly high. An off-station experiment in a plot at the Merritt orchard in Skagit County, begun in 1995, was continued in 1996 and 1997 to evaluate the effect on Jonagold apple quality of potassium and magnesium applied granularly in the fall and through fertigation during the growing season. The latter Jonagold orchard was in its fifth leaf in 1998. The site at the station had been under the experimental fertility regime for four years, and 1998 was the third year for data collection from that plot. The project was initiated in the spring of 1995 and completed in the fall of 1998.