08.08.2024
A new study by the Leibniz Centre for Agricultural Landscape Research (ZALF) in the journal Heliyon shows that the mixing of less fertile subsoil into the topsoil due to erosion has only a minor influence on the efficiency of nitrogen fertilizers. It is much more important to know the soil type in order to optimize the use of the fertilizer form.
Erosion, i.e. the removal and displacement of topsoil by wind and water, leads to a loss of 35.9 billion tons of soil material every year. This not only reduces soil fertility, but also crop yields. In a study, researchers from the Leibniz Centre for Agricultural Landscape Research (ZALF) wanted to find out what influence the mixing of topsoil and subsoil caused by erosion and the degree of erosion of the soil as such has on the dynamics, efficiency and storage of various forms of nitrogen fertilizer.
Investigation of nitrogen fertilizer forms and soil types
The topsoil is rich in nutrients and organic material. This is where the main growth of the plant roots takes place. Below this are different, less fertile subsoil layers, which differ from each other in terms of their chemical properties and rootability.
Three soil types with different degrees of erosion were investigated in a pot experiment:
- Non-eroded Luvisols are often found in temperate climate zones and are characterized by clay displacement into deeper soil layers; they have a deeply rootable soil profile
- Eroded Luvisoils; the number and depth of easily rootable subsoil layers are reduced
- Extremely eroded Pararendzina; very shallow soil profile, thus the topsoil is characterized by the calcareous, hardly rootable initial substrate of the soil formation (boulder clay), which is directly adjacent to the topsoil
Each of these soils were treated with either mineral (calcium ammonium nitrate) or organic (biogas digestate) nitrogen fertilizer. The scientists mixed 20 % of the respective subsoil into the topsoil to simulate the consequences of a current topsoil removal and observed how this affects the dynamics and utilization of fertilizer nitrogen.
The study showed that the fermentation residue nitrogen was stored in the soil to a greater extent than calcium ammonium nitrate. At the same time, the efficiency of fertilizer utilization by the plants was lower for the digestate than for the calcium ammonium nitrate. The effect of the soil type was more pronounced than that of the incorporation of subsoil, both in terms of storage in the soil and utilization by the plants. It was also shown that the eroded soils had a higher capacity for nitrogen storage, which can be attributed to their higher clay content in the subsoil.
Importance of fertilization for the nitrogen cycle
Nitrogen is one of the most important plant nutrients that must be constantly replenished in the form of special nitrogen fertilizers to ensure a high and stable production of food and animal feed. However, too much fertilizer increases environmental pollution through the increased release of nitrate into the groundwater and of ammonia and the greenhouse gas nitrous oxide into the atmosphere. This is due to the acceleration of the conversion processes caused by a large number of microorganisms in the soil as a result of nitrogen fertilization.
"Our study shows that the form of nitrogen fertilizer and the soil type altered by erosion determine how the nitrogen behaves in the soil, how it is taken up by plants or whether it is lost through leaching into the groundwater or by gaseous emissions," explains Isabel Zentgraf, the lead author of the study. "In contrast, the incorporation of subsoil caused by erosion had a surprisingly small effect on the nitrogen cycle."
Significance for agriculture
The findings are particularly relevant for the development of sustainable fertilization strategies. Above all, farmers can improve the efficiency of fertilization by selecting the right form of nitrogen fertilizer and taking the soil type into account, while the erosion-related mixing of subsoil into the topsoil appears to be of less importance in this respect. "However, further research is necessary in order to develop long-term strategies for nitrogen fertilization on eroded sites based on these findings," adds Zentgraf.
Project partner:
- Leibniz Center for Agricultural Landscape Research (ZALF)
- Johann Heinrich von Thünen Institute Federal Research Institute for Rural Areas, Forestry and Fisheries
Funding information:
This study was supported by the Federal Ministry of Food and Agriculture BMEL (FNR Grant: 22404117) as part of the "Krumensenke" research project.
Further information:
To the publication:
https://doi.org/10.1016/j.heliyon.2024.e34822
Note on the text:
This is a summary of the original text created with the help of artificial intelligence: Zentgraf, I., Hoffmann, M., Augustin, J., Buchen-Tschiskale, C., Hoferer, S., Holz, M. (2024) Effect of mineral and organic fertilizer on N dynamics upon erosion-induced topsoil dilution. Heliyon 10, 15, e34822. https://doi.org/10.1016/j.heliyon.2024.e34822, published Open Access under license CC BY 4.0 https://creativecommons.org/licenses/by/4.0/. The text has been carefully reviewed and revised in the light of the AI regulations at ZALF.
