Once but you can’t just look at how much one person has had to add something and compare it apples to apples with what someone else may have added. Remember that soils with higher clay contents hold nutrients much better to begin with than sandy soils. What you can look at though is the improvement in your own plot over time. As an example, lets look at my K use over the last few years (potash).

Back when I tilled, I didn’t have this build up of dark organic matter you see in the pic. To put it another way, I didn’t have the reserve of negatively charged ions that I have now. Therefore, when I added in positively charged nutrients like K (potash)…there wasn’t much there for it to bond to. My soil tests would go from around 60 lbs of K up to 110 or so…and then right back down to the basement by the next planting. As a comparison, this year when I tested, my K levels were 220 lbs per acre and the last time I added potash was in the early spring. It didn’t call for any at planting. Because I’ve added in all of the negatively charged OM to my soil, I’m holding onto all of the positively charged nutrients better now. They have something to bond to. This includes Ca or lime. I’ve brought in lime once this past spring to correct the bottoming out of my Ca that had occurred during the tillage years. I actually waited an extra year before doing so to give this OM layer time to build. In other words, I didn’t spread it until I had built something to hold it.