Fertigation can be as simple or as complex as one wants to make it. It can be as simple as an inline injector you fill with 1/2 strength fertilizer of choice and plug it in every time the plants need water. You learn when the plants need water by understanding your soil and the effect your weather has on it. And that it different for each garden.

Or one can get buried under PPM ratings and fixated on an inflexible watering schedule. Unfortunately that approach usually only works with hydroponics in a heavily environmentally controlled environment like a GH. If that is the case then the Hydro Forum is where you need to post.

So assuming these are inground plants, growing outdoors, and that you will be using drip tape, soaker hose, or drip hose with emitters (not recommended) then the easiest and most budget-minded system is any of the simple in-line injectors on the market. They are clear in color so you can see when the colored fert is gone in the reservoir. If the fert you use does not color the water then add a couple drops of food coloring or switch to one that does. Water goes in one side, mix with the fertilizer, and goes out the other side into the hose and into the soil.

Just as with soil moisture, consistency of the levels of water and nutrients is the goal. So the goal isn't an exact PPM at a specific time as with hydroponics but a consistent level of nutrients the plants need at this stage of their growth. As the plants mature they need more nutrients but they also need more water so fertigation provides both.

Hope this helps some.

Dave