If they are lacking in chlorophyll, then they don’t manufacture as much food as they should and the crop will be smaller than it should be. A low nitrogen uptake reduces the amount of proteins and amino acids created by the plant which reduces the quality.
So, is there enough nitrogen in the nutrient concentrates you buy? Yes, usually there is as long as you have bought a quality nutrient.
The problem is not only in the amount of nitrogen but also in the form as well as in the amount of other nutrients and non-nutrient salts in the solution. For instance, total nitrogen levels should be 55% to 65% higher than calcium. Interestingly chloride (common in tap water) can inhibit the uptake of the nitrate form of nitrogen. Actual nitrogen loss (known as denitrification) can also occur from the nutrient solution, especially in warmer conditions. To further complicate matters the form of the nitrogen required changes from a higher nitrate to a higher ammonium requirement when plants move from the growing stage to the flowering stage. We are, of course, trying to supply our plants a balanced solution around the plant’s roots and this balance changes according to plant uptake. So while the nutrient concentrate might be well balanced at the start, the plant may have made the solution unbalanced. This means that the correct form of nitrogen may not be available according to the plant’s exact needs.
In twenty litres of freshly made up nutrient solution there is only about 2-6 grams of nitrogen. When you consider how much actual nitrogen there is in the nutrient solution it’s not hard to see how a small amount lost can lead to big changes in availability. By the time the plant has taken some up, the biological activity has consumed some and some has been lost through denitrification, it doesn’t take long before there is a serious nitrogen shortage in your system.