Elizabeth Crain

Nitrogen (N) is one of the most important drivers of agricultural production. Close to 100 million tons of N are fixed industrially by the Haber Bosch process. An important alternative form of creating N that plants can use is biologically fixed nitrogen. White clover (Trifolium repens L.) does this very effectively. It forms a symbiotic relationship with soil bacteria called rhizobia. The rhizobia fix atmospheric nitrogen (N2) into a form that can be readily utilized by the plant. In exchange for the fixation of nitrogen, clover provides starches and sugars through its root system to the rhizobia, this process is called Biological Nitrogen Fixation. BNF is very costly to legumes, as they use a lot of energy and photosynthates, so legumes like clover will use soil N if it is available before fixing atmospheric N. Previous studies have found that the addition of N fertilizer in clover/grass pastures results in a reduction in clover production and N2 fixation. The reduction in BNF is due to the utilization of soil N over fixed-N, which could result in a net loss or stagnation in the amount of biologically available N in the soil. I found that the past use of chicken litter (high nitrogen content in soil) reduces the quantity of atmospheric nitrogen White Dutch Clover fixes over the course of a season. Clover in the high nitrogen plots fixed less nitrogen than clover in low nitrogen soils.