Synthetic fertilizers are one of the major line items when evaluating a farm budget, often landing between 30%-40% of costs (T. Wang) depending on the crop, prices, and practices. Fertilizer prices climb through scarcity events and are closely tied to oil prices leading to fluctuations that can render farmers vulnerable to large price increases. While prices tend to ebb and flow, it is likely that the heightened political focus on climate change and reducing carbon footprints will continue to increase prices over the long term, and with recent geopolitical turmoil spiking prices in recent years, more growers are looking for alternatives that will permanently reduce their fertilization costs without sacrificing yields.

As it stands, usage of synthetic fertilizers has persisted as a wasteful practice with 50% or more of applied nitrogen fertilizer never reaching the crop. Beyond losing half of the investment put into your land, there are carryon environmental effects including coastal hypoxia (learn more here), nitrous oxide gases expelled into the atmosphere, and nitrogen deposition into natural habitats (G. Philip Robertson). Plants that hold too much nitrate in their leaves also become susceptible to pest damage, meaning that over applying can damage plants as well as harm the environment.

How do we then reduce nitrogen waste while optimizing nitrogen access to the plant?

NUE (Nitrogen Use Efficiency)

NUE is the concept of optimizing your nitrogen fertilization. Over the years different concepts and technologies have been implemented to help reduce nitrogen losses, for example, adding coatings that act as inhibitors can help to slow down nitrogen release resulting in more uptake for the plant (Mahmud). This strategy is roughly in line with more precise applications, often splitting nitrogen applications to allow for “spoon feeding” the crop. The main goal is to utilize soil analysis, plant analysis, and technologies that can synthesize data like rainfall and solar days to estimate the exact nitrogen need of the plant. If we know how the plant uses nitrogen, we can match that usage and minimize environmental losses. Generally, this is a great strategy, it does require more frequent applications making implementation a tradeoff between compaction and main power vs. plant nitrogen uptake. For most farmers, it is more cost efficient to apply one or maybe two large applications even though much of the fertilizer is lost.

Nitrogen can also get tied up in organic carbon in the soil, while this may seem wasteful at a first glance, eventually that nitrogen will get mineralized back into the soil in a plant available form. Including practices that encourage residue to remain in the field and that increase organic matter are great options to leverage the soil’s capacity to incorporate nitrogen. Finding the equilibrium between nitrogen tie-up and the nitrogen that can make it into the plant is certainly a difficult balancing act. Plants need nitrogen through early vegetative stages in row crops like corn but not so much once they start to tassel. We find that building soil health that can support nitrogen incorporation into the biomass and limit nitrogen losses helps to reduce the synthetic nitrogen needs of the plant. It can be helpful to utilize some synthetic nitrogen to give that initial burst of growth through the early vegetative stages of a crop, but we can severely limit nitrogen losses through improved soil.

Nitrogen loss is greatest in soils with poor structure

In line with increasing soil health is improving soil structure. When talking about soil structure we are referencing the ability of the soil to form aggregates. Soil aggregates are formed from microbes in the soil that secrete glue-like substances that bind soil particles together. The results of well-structured soil include better aeration, water retention and drainage, reduced erosion, and will typically have higher levels of organic matter. In many ways it is easier to look at the impacts of unstructured soil to highlight the impact that soil structure plays on the nitrogen cycle.

In compacted, poorly structured soil it becomes difficult for oxygen to enter the soil media, resulting in a community of predominantly anaerobic microbes. Anaerobes are far more likely to volatilize sources of nitrogen leading to excessive nitrogen losses. Some factors like temperature, pH, rainfall, and incorporated organic matter will influence how quickly oxygen is used, optimizing these factors can help to reduce volatilization.

Improvements to soil porosity allow for water to penetrate deeper into the soil, helping to reduce erosion which carries organic matter and nutrients away from the crop. Well structured soil also increases the water holding capacity of the soil, so the water that penetrates has somewhere to go and will not runoff carrying nitrates away with it.

(Yoshinari)

Practices make a large impact on how nitrogen reacts in the soil. Cover crops, for example, can help to reduce the soil temperature, maintain structure, and increase organic matter helping to increase oxygen content. Reducing or eliminating tillage improves water management and prevents organic matter from rapidly decomposing in low oxygen environments. Cultivating a healthy aerobic microbiome stimulates solubilization of nutrients and helps to limit nitrogen losses.

Microbial effect on Plant growth and reduction of fertilizer usage

Adding diverse aerobic microorganisms to the soil is possibly one of the best ways to help increase NUE. Microbes can help to decrease the need for nitrogen fertilizer through nitrogen fixation, improve nutrient availability, and increase root mass/absorption area (Di Benedetto). Effectively, improving the microbial community better leverages each pound of nitrogen that is put into the ground and will even add nitrogen to the soil system. In our experience we have seen fertilizer reductions of greater than 20% when implementing beneficial microbes into growing systems, we have even managed to completely remove synthetic fertilizers from some farms.

At the end of the day, modern farming needs to learn how to better leverage natural resources to limit external inputs. There is no one practice that is going to solve all of conventional agriculture’s problems, in reality the practices mentioned in this article are additive. Microbes will flourish in no till systems where they can develop ecological niches without annual disturbances and cover plants will help to reduce compaction in no-till systems. Taking steps to incorporate new technologies and practices takes time, but it is well worth the effort to reduce costs and to limit the damage that is done to our environment.

Resources

Wang, T. (2023). Impact of High Fertilizer Prices and Farmer’s Adaptation Straregies in the U.S. Midwest. Agricultural and Applied Economics Association, 38(4), 1–13.

Hypoxia. NCCOS Coastal Science Website. (2024, May 21). https://coastalscience.noaa.gov/crp/hypoxia/

How to manage pests. UC IPM Online. (n.d.-b). https://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISORDERS/nitrogenexcess.html#:~:text=Excess%20nitrogen%20can%20cause%20plants%20to%20grow%20excessively,reducing%20their%20fruit%20production%20and%20delaying%20fruit%20maturity.

Robertson, G. P., & Vitousek, P. M. (2009). Nitrogen in agriculture: Balancing the cost of an essential resource. Annual Review of Environment and Resources, 34(1), 97–125. https://doi.org/10.1146/annurev.environ.032108.105046

Antonella Di Benedetto, N., Rosaria Corbo, M., Campaniello, D., Pia Cataldi, M., Bevilacqua, A., Sinigaglia, M., & Flagella, Z. (2017). The role of plant growth promoting bacteria in improving nitrogen use efficiency for sustainable crop production: A focus on wheat. AIMS Microbiology, 3(3), 413–434. https://doi.org/10.3934/microbiol.2017.3.413

Yoshinari, T. 1993. Nitrogen oxide flux in tropical soils. TREE. 8:155-156.

Mahmud, K., Panday, D., Mergoum, A., & Missaoui, A. (2021). Nitrogen losses and potential mitigation strategies for a sustainable agroecosystem. Sustainability, 13(4), 2400. https://doi.org/10.3390/su13042400