Nitrogen (N) is the most limited nutrient for crop growth. Choosing a leguminous cover crop adds N to your system in a relatively easy and inexpensive way. Leguminous crops such as clovers, lupines or vetches fix atmospheric N in a symbiotic relationship with soil bacteria called rhizobia. This reduces the reliance on fertilizer N and maintains an efficient, low cost farming system. Legumes will utilize soil N first if it is available, then fix sufficient N to satisfy any remaining demand. Both, uptake of soil N and N fixation can occur simultaneously. Potential N fixation from legume cover crops can reach up to 200 kg N/ha/year, but factors such as mineral N, moisture stress, low soil fertility, grazing, temperature, weed competition and appropriate Rhizobium strains can affect this. It is important that other nutrients, notably phosphorous are at sufficient levels for plant growth.