Nitrogen (N) is an essential element for all life. Nitrogen is required for the synthesis of amino acids and proteins, which are the building blocks of all life and are essential for all vital processes in plants. Although our atmosphere is mostly nitrogen gas, plants are unable to capture this form of N, and instead must rely on nitrogen fixed by microbes or added to the soil by farmers. Nitrogen is often the limiting nutrient in the growth of plants. Poor agricultural practices have depleted many soils of their N, inhibiting the growth of plants and microorganisms alike.
Nitrogen and Carbon
Carbon sources, in tandem with nitrogen fertilization, build soil health.
Nitrogen
Figure from Diacono, M. and Montemurro, F. (2010). Long-term effects of organic amendments on soil fertility. A review. Agronomy for Sustainable Development.
Studies on Nitrogen and Carbon Complexing
In a 33-year long field experiment comparing various fertilization regimes in wheat, the authors found that a recommended dose of inorganic nitrogen fertilization alone caused yields to decrease over time. However, the application of inorganic nitrogen amended with manure caused yields to significantly increase over time, and increased soil organic carbon by 38% over the course of the experiment.
In a 50-year long term experiment that compared the effects of mineral fertilization to reduced mineral fertilization with an amendment of either farmyard manure or crop residues, the authors found that the farmyard manure treatment had a significant positive effect throughout the whole experiment. Compared to mineral fertilization alone, the farmyard manure treatment had an average of 4% increased yield. The farmyard manure treatment also significantly increased soil organic carbon as well as total microbial biomass.
In a meta-analysis of multiple long term field experiments, Korschens et al. (2013) found that fertilizing with combined organic and mineral fertilizers increased yield an average of 6% compared with optimal mineral fertilization alone. This percentage varied between crop species, ranging from 3% (winter wheat) to 9% (potatoes).
Why Complex Nitrogen with Carbon?
The need for nitrogen (N) in agricultural systems is well known. N deficiency severely hinders plant health, inhibits cell division and chloroplast development, and reduces overall dry yield. To prevent these symptoms from arising, nitrogen fertilizers are widely used to obtain optimal yields and growth rates. However, the long-term application of inorganic mineral fertilizers causes the depletion of organic matter in the soil, which has caused declining soil fertility in many areas of the world.
Mineral nitrogen fertilizers can be quickly leached out of the soil and into groundwater. This not only makes the fertilizers unavailable to the target crops and wastes the money of the farmer, but also damages nearby ecosystems through a process called eutrophication.
Applying nitrogen fertilizers in tandem with soluble carbon sources is less stressful for the plant, and allows the applied nitrogen to be more efficiently taken up and converted into organic compounds. The organic compounds provide high surface area for ions to adsorb to. Nitrate in the soil is able to bind to these organic compounds, preventing it from leaching into the groundwater. Applying nitrogen with carbon sources can also benefit the microbial community by maintaining an optimum carbon-to-nitrogen ratio, creating higher microbial diversity and a greater abundance of nitrogen-mineralizing bacteria.
Common, inexpensive sources for carbon include manure, compost, biochar, and straw. While using these carbon sources alone as a soil amendment does not typically meet the plant’s nutritional requirements, applying manure or compost in addition to nitrogen fertilizers can significantly improve soil quality relative to mineral nitrogen fertilizers alone.
Photo of nitrogen deficiency symptoms in soybean. Image from Wikipedia.
Further Reading
Berthrong, S. T., Buckley, D. H., and Drinkwater, L. E. (2013). Agricultural management and labile carbon additions affect soil microbial community structure and interact with carbon and nitrogen cycling. Microbial Ecology.
Blanchet, G., Gavazov, K., Bragazza, L., and Sinaj, S. (2016). Responses of soil properties and crop yields to different inorganic and organic amendments in a Swiss conventional farming system. Agriculture, Ecosystems and Environment.
Diacono, M. and Montemurro, F. (2010). Long-term effects of organic amendments on soil fertility. A review. Agronomy for Sustainable Development.
Korschens, M., Albert, E., Armbruster, M., et al. (2013). Effect of mineral and organic fertilization on crop yield, nitrogen uptake, carbon and nitrogen balances, as well as soil organic carbon content and dynamics: Results from 20 European long-term field experiments of the twenty-first century. Archives of Agronomy and Soil Science.
Laird, D., Fleming, P., Wang, B., Horton, R., and Karlen, D. (2010). Biochar impact on nutrient leaching from a Midwestern agricultural soil. Geoderma.
Sanchez-Martin, L., Vallejo, A., Dick, J., and Skiba, U. M. (2008). The influence of soluble carbon and fertilizer nitrogen on nitric oxide and nitrous oxide emissions from two contrasting agricultural soils. Soil Biology & Biochemistry.
Yang, J., Gao, W., and Ren, S. (2015). Long-term effects of combined application of chemical nitrogen with organic materials on crop yields, soil organic carbon and total nitrogen in fluvo-aquic soil. Soil & Tillage Research.
