There are two main effects of elevated CO₂ on the nitrogen nutrition and growth of vegetable crops:

First, as CO₂ levels increase, the level of nitrogen in the tissue of plants decreases. This is due to more efficient use of nitrogen by plants grown at high CO₂ and means that less nitrogen is required to produce maximum yields than would be required at 1990 levels of CO₂. For example, in cucumbers, spinach and fenugreek, N concentrations in the leaves were about 16% lower at high CO₂ compared to plants grown at ambient CO₂ levels.

The implication of this is that if CO₂ levels continue to rise, vegetable crops will become more efficient in their use of nitrogen and therefore less will need to be applied. This may fit well with methodologies aimed at reducing N₂O emissions based on better nitrogen management as part of the Carbon Farming Initiative.

The other main impact of nitrogen relates to the growth and yield stimulation that can be expected at higher CO₂ levels. This response is highly dependent on the supply of nitrogen to the plants, as plants need adequate nitrogen to take advantage of the benefits of elevated CO_2.