2018 ASHS Annual Conference

Vegetable crops produced in the Arizona desert have always shown large yield and quality responses to N and P fertilization. Soil test based fertilizer recommendation of N and P have been developed by the Universities and N and P fertilizers are commonly used to optimize production. Because our irrigation water has K, and our soils have abundant K-bearing minerals, response to K fertilizers are very infrequent and K fertilizers are rarely used. This desert region in Arizona has been classified as an area prone to Zn deficiency. This is due to soil pH values greater than 7.5, and the presence of carbonate that ties up plant available Zn. However, measured crop responses to Zn had been lacking and the routine application of Zn fertilizer could not be economically justified. More recently, we have found spinach produced in this region often showed yield responses to low levels of Zn fertilization. In fact, we observed spinach yield responses in about 50% of the field studies we conducted. Interestingly, in a follow-up survey we found about 50% of the soils used for spinach production had DTPA soil-test Zn levels less the 1 ppm indicating a response to Zn was possible.