Nitrogen is a very mobile nutrient.
It’s very likely the rain brought them a bunch of fresh nitrogen. I’ve seen tobacco literature warn about adding nitrogen to the soil early, only have it washed away by rain.
Page 33 talks about losing it, but the whole nitrogen section (starting on page 30) talks about how soil types really affect the nitrogen’s movement in rain:
It’s very likely the rain brought them a bunch of fresh nitrogen. I’ve seen tobacco literature warn about adding nitrogen to the soil early, only have it washed away by rain.
Page 33 talks about losing it, but the whole nitrogen section (starting on page 30) talks about how soil types really affect the nitrogen’s movement in rain: