Although organic matter plays an important role in building productive soils, there are specific crops and soil types that will benefit from additional applications of specific nutrients. Organic farmers are allowed to use a variety of fertilizers to provide micronutrients to their crops. Before applying micronutrients, soil deficiencies must be documented through soil tests, plant tissue tests, observing the condition of plants, or evaluating crop quality at harvest.
Nitrogen is often a limiting nutrient, especially for vegetables and other row crops. Including legumes in the rotation can help to ensure sufficient nitrogen for the following crop. Biological nitrogen fixation in legumes results from a symbiotic relationship between the plant and Rhizobium bacteria. These bacteria “infect” the roots of legumes, forming nodules. The bacteria then fix nitrogen from the air, which results in sufficient nitrogen both for their own needs and for subsequent crops.
The inoculation of legume seed may be necessary to optimize nitrogen fixation. Be certain that you are purchasing an inoculant appropriate to the kind of legume you are planting and verify that it is not genetically modified. Genetically modified inoculants are prohibited in organic production.