This evening I sprayed on the ground a liquid iron/sulfur fertilizer. It also had micro amounts of zinc, copper and other nutrients. Iron is a very import nutrient for plants. It is in the process of making chlorophyll. It is also involved in making of most of a plants enzymes. A plant doesn't need a lot of iron to grow healthy, but too little will cause chlorosis which shows up as yellow leaves.
The elemental sulfur will help drop soil pH. My pH is too high, like most western soils. As bacteria in the soil break down the sulfur an acid is produced, which helps drop the soil pH and more nutrients can become available to the plant.