Spinach/Lettuce
Arkansas research showed that spinach response to applied N is restricted when plants are deficient in S (Wells et al., 1990). Both yield and color were enhanced when 20 lb/ A of S was applied with 160 lb of N/A (Table 1).

In other research, spinach leaves fertilized with SOP showed the lowest moisture loss by about 5 percent. This results in better storage quality from the use of SOP (Grutz, 1953). Sulfate of potash also provides for higher dry matter yields due to less water content in leaves (Malavolta et al., 1962). Lettuce is damaged by high salt concentrations in soils, but KCl increases fresh yields due to water fill. Because SOP increases sugar content and vitamin C, an ideal fertilizer would be a combination of the two forms.

Table 1.
Yield and color quality of spinach as influenced by N and S fertilization.