Earth into Light

Nitrogen, or simply N on the periodic table of elements, is the principal component of proteins we eat and the most limiting nutrient to plant growth. Growers supplement plants with N in the form of fertilizers. Either organic, such as manure, compost or leguminous cover crops – or not; N available to plants transforms into an inorganic state for plant uptake. With exceptions, plants take up N in two principal forms; ammonium and nitrate. Together they form an early pathway to food ending up on the plate.

Nitrogen Use Efficiency
I wrote about N-use efficiency last year in regard to my PhD research project. The discourse over N-use efficiency is an ongoing debate because one, N sources are derived from fossil fuels and two, N fertilizer is lost to the environment. Without bringing in a doomsday scenario or polarizing politics, estimates of N-use efficiency are difficult to make because of three reasons:

1) Estimates are based on data from field stations rather than grower’s fields

2) Calculations factor in inputs and exports without accounting for internal soil cycling

3) Measurements of indigenous nutrient supply requires unfertilized land with crops.

Where does the rest of the N go?
Two places N accumulates are the atmosphere and groundwater. Accumulation of nitrates and the gasses ammonia, nitric oxide and nitrous oxide has a known adverses effect on the environment. A third place where N goes when out-of-reach by plant roots is the soil. Nitrogen immobilization by soil microbial organisms is one sink for N, often overlooked or accounted as a N loss from the system. Dr. John Stark wrote to Nature in 1997 about this miss-observation in undisturbed coniferous forests in the U.S. West.

Strategies
Strategies to enhance N-use efficiency are site and crop specific and require a careful understanding of yield and management practices. Not only do we need to improve fertilizer-use in today’s world but, we must “optimize indigenous soil N supply” (Ladha et al. 2005). Various strategies are shared among agriculturalists to improve N-use efficiency but, solutions to the problem may under value the role of the farming industry.

References
J. K. Ladha, H. Pathak, T. J. Krupnik, J. Six and C. van Kessel “Efficiency of Fertilizer Nitrogen in Cereal Production: Retrospects and Prospects” in Advances in Agronomy 87 2005.
J.M. Stark and S.C. Hart “High rates of nitrification and nitrate turnover in undisturbed coniferous forests” in Nature 385, 61-64 (02 January 1997).