A very collaborative semester in Switzerland!

ESR-4 Tomas Sitzmann, ESR-8 Mario Alejandro Alvarez Salas, & ESR-10 Pietro Mendonca de Santis Sica

Pietro and Tomas completed their secondment at ETH! From September until December 2021 they were in Switzerland carrying out experiments related to their research topics in collaboration with Astrid Oberson, Federica Tamburini, and Mario. In the meantime, Tomas, Pietro, and Mario attended the course ‘Chemical Nature of Nutrients and their Availability to Plants: the Case of Phosphorus”. In this course, Professor Frossard and the students discussed mechanistic relationships between nutrient speciation in the fertilizer, nutrient dynamics in the soil, and nutrient uptake by plants, using P as an example.

During the secondment, Pietro and Mario were collaborating in the process of extracting phosphates out of various soil treatments and purifying the extractants until obtaining silver phosphate (Ag₃PO₄ ). The purification of soil samples is needed for the later analysis of the oxygen isotopes (δ¹⁸O-P) in phosphates. Phosphate purification is a challenging task, and several adjustments needed to be made in order to obtain purificates of good quality. After several discussions with Federica Tamburini, one of the main developers of δ¹⁸O-P isotopic techniques in agronomy, adjustments have been done to the purification process. The use of δ¹⁸O-P will provide exciting insides on the microbial turnover of phosphates, in various experiments that Pietro and Mario are conducting.

Tomas worked with Astrid in a greenhouse experiment testing the fertilizer use efficiency from a close mixture of vermicompost and mineral fertilizers. He fertilized his pots with a combination of vermicompost with potassium phosphate solution labeled with isotopes of phosphorus (³³P) and ammonium sulfate solution labeled with an isotope of nitrogen (¹⁵N). This mixture tried to emulate a grain of an organo-mineral fertilizer (OMF) and was created to test if the close contact of an organic material with the mineral fertilizers influences the growth of Italian ryegrass (Lolium multiflorum Lam.) differently than the mineral fertilizers alone. Previous works have shown that the OMFs could have a slower release of nutrients than conventional fertilizers; therefore, plants can absorb the nutrients during a more extended period of type. Ryegrass is an excellent plant to test this kind of experiment because it is possible to harvest the same plant several times and study how the uptake of nutrients changes over time. The isotopes were used as tracers to determine how much of the nitrogen and phosphorus uptake by the ryegrass was coming from the mineral fertilizers and how much was coming from the soil. Tomas has already finished growing and harvesting his plants; let’s see what he found out of his experiment!