I can't give you advice, as I'm not an expert, but I can again direct you to the plant clinics by the extension office, where you need photos and grass samples and can also get a cheap Ph test for soil. Also bring the history of what has been put on the lawn.
I CAN tell you what I'm doing for my poor lawn. I have empire zoysia on top of sandy clay which is alkaline and poorly drained. I am adding organic material on top of the grass (ex. peat, clippings, black kow) , aerating with an implement or cleats, as well as following advice to add chelated iron as in the article below, iron deficiency is there identified as likely to cause yellowing. I'm watching the wetter areas to see if action is needed to sculp the surface or reduce water. Let's hope we are successful.
https://edis.ifas.ufl.edu/lh011
quote:
Since zoysiagrass is very slow to green-up in the spring, avoid applying fertilizer until after the turf has become fully green to avoid premature green-up, which is prone to frost injury. This is especially important in North Florida, where late spring frosts may damage the grass. Delaying spring fertilization until the turf is actively growing and can use the fertilizer also reduces the potential for nitrogen leaching from fertilizer. Likewise, don't fertilize too late in the year, as this can slow regrowth the following spring. An application of iron can enhance spring green-up. Applying nitrogen on zoysiagrass in early spring and late fall significantly increases the risk of large (brown) patch disease.
On high-pH (> 7.0) soils or where high-pH water is applied, yellow leaf blades may be an indication of iron or manganese deficiency. Application of soluble or chelated sources of these micronutrients can provide a green-up due to elevated pH.
For iron deficiency, spray ferrous sulfate (2 ounces in 3–5 gallons of water per 1000 square feet) or a chelated iron source (refer to the label for rates) to temporarily enhance color. Iron applications every 6 weeks help maintain green color and, unlike nitrogen, do not promote excessive top growth.
Note that iron is not a substitute for nitrogen, which provides the building blocks for turfgrass growth and is required for turf health. While both iron and nitrogen deficiencies result in yellowing of turfgrass, they are distinctly different deficiencies in plants. Applying iron does not cure yellowing due to nitrogen deficiency, and iron fertilizer is not a substitute for nitrogen fertilizer. Foliar iron fertilizers, such as iron sulfate or chelated iron solutions, help cure iron deficiencies, and nitrogen fertilizers applied according to BMPs cure nitrogen deficiencies.