What Is Nitrogen Deficiency?
As the name indicates this deficiency is the plant showing that it doesn’t have enough Nitrogen to grow. How does she solve this situation? By sucking it out of the older sections of the plant (aka lower leaves). This is why you see the leaves change color and crisp up.
If you’re seeing this don’t worry, Nitrogen Deficiency is one of the most common deficiencies that indoor growers of all levels cross. The fix is generally pretty straight forward.