Nutrient Fluxes in Soil-Plant Systems: The Case of Nitrogen

Abstract

The course teaches knowledge and experimental techniques to study and evaluate pools and processes underlying nutrient fluxes in soil-plant systems. Theory and methods concern i) nitrogen dynamics in soil, ii) the use efficiency by crops of nitrogen added with fertilizers, iii) the fate of fertilizer nitrogen not taken up by the crop and iv) symbiotic N2 fixation by legumes.

Objective

Using the element nitrogen (N) as model case, the student gets familiar with techniques to assess the dynamics and availability of nutrients in the soil-plant system and to determine the use efficiency by crops of nutrients added with fertilizers. The student learns how to use and apply 1. stable isotope techniques for analyzing nutrient fluxes in soil-plant systems, and 2. biochemical methods to obtain indicators on nutrient transformations. The student is able to critically evaluate the tools used in agricultural or environmental studies dealing with fluxes of elements in soil-plant systems, and the interpretation of results. Knowledge about processes and pools underlying nutrient cycles in agro-ecosystems will be improved. Finally, the acquired knowledge gets applied for writing an expert opinion on a nitrogen related problem in agriculture. The student learns to work in the laboratory, to organize work in groups, to evaluate and interpret, to look for information outside of the course (e.g., in the library), to read and analyze this information critically, and to combine it with the results of the experiments. Students get trained in presenting results, both written and orally. Finally, they apply the acquired knowledge to a real problem related to the course matter.

Content

This course provides theoretical knowledge and teaches methods to analyze the dynamics of elements in soil-plant systems and to determine the use efficiency by crops of nutrients added with mineral and organic fertilizers. Nitrogen (N) will be used as model case. It provides information about various techniques (isotopic, chemical, biochemical) that can be used to evaluate i) content of elements in fertilizers, soils and plants; ii) availability of elements in soils and fertilizers for plants; iii) transfer of elements from a fertilizer to a crop; iv) symbiotic N2 fixation by legumes. The course starts with revisiting the N cycle in agriculturally managed soil-plant systems, as affected by different fertilizers. Then a background on stable isotope biogeochemistry, with focus on stable N isotope use at natural abundance and with isotope enrichment, is provided. To test the transfer of N contained fertilizers from the soil to the plant, a pot experiment (glasshouse study) is designed. It includes two test plants and fertilization treatments, both with 15N labeled organic fertilizer and appropriate reference treatments. The soil is characterized for basic chemical properties and for biochemical characteristics that are related to the N dynamics. Plants are harvested and analyzed for their dry matter production, their N isotope composition and N content. From the direct (15N) labeling approach, the proportion of N in the plant derived from the added fertilizers and the percentage of added fertilizer recovered in plant material is calculated. The 15N analyses in the soil and in the plant material after the crop cycle allows drawing a balance of the added fertilizer and discussing N losses. Data on 15N isotopic composition in legume and non-legume plants are used to compare the 15N Natural Abundance and the 15N Enriched Dilution methods to estimate symbiotic N2 fixation by the legume. The results get combined and illustrate the role of the various N sources (fertilizer, soil, atmosphere) for N uptake by the plant. The experiments are carried out by the students supervised by group members (three senior scientists, PhDs, laboratory staff). The students carry out data analysis, results calculations and present them orally. At the end of the course, they apply their knowledge to a real problem related to the use of nitrogen in agriculture, and present their outcome in form of a written expert opinion.

Resources