Untersuchungen zur Phosphatmobilität und – verlagerung in Dauerfeldversuchen auf Sandböden

Ziel der Untersuchungen war, das Phosphorverlagerungspotenzial karbonatfreier, sandiger Ackerböden unter den subkontinental geprägten Klimabedingungen Brandenburgs (Nordostdeutschland) auf Grundlage von standortrepräsentativen Langzeitdüngungsversuchen zu bewerten. Es erwies sich, dass die untersuchten Standorte durch ein erhebliches P-Verlagerungspotenzial gekennzeichnet sind. Die Höhe der Phosphorverlagerung war abhängig vom langjährig kumulierten P-Düngesaldo. Vom überschüssig gedüngten Phosphat verbleiben nur 63% im Pflughorizont, etwa 90 % jedoch im effektiven Wurzelraum bis 75 cm Tiefe. Hohe P-Gleichgewichtskonzentrationen der Bodenlösung von > 1 mg l-1 traten im tieferen Unterboden nur bei extremer P-Überdüngung auf. Ein Einfluss der P-Düngeform auf die P-Mobilität im Boden wurde nicht deutlich

C- Speicherung und N-Bilanz im effektiven Wurzelraum in sandigen Ackerböden nach langjährig differenzierter Düngung

In Dauerdüngungsversuchen (Groß Kreutz, Brandenburg) auf typischen Ackerböden der sickerwasserbestimmten, sandigen Grundmoränenstandorte wurde über mehr als 40 Jahre unterschiedlich mineralisch und/oder organisch gedüngt. Bei Gesamt-N-Gaben von 0-150 kg ha-1 a-1 haben sich der C- und N-Vorrat im Ober- wie im Unterboden deutlich differenziert. Zum Untersuchungszeitpunkt hatten sich im Boden bis in 70 cm Tiefe 32 - 50 t ha-1 Corg und 2,1 – 5,5 t ha-1 Nt akkumuliert. Im Mittel der Prüfglieder befanden sich bis zu 37 % des Corg- und 32 % des Nt-Vorrates im Unterboden. Die Pflanzenwurzel muss einen bedeutenden Anteil an der C-Speicherung im Unterboden haben, da bei steigender Mineraldüngung und steigenden Erträgen der C-Vorrat nicht nur im Oberboden sondern auch im Unterboden zunimmt. Die N-Bilanz des Bodens verbessert sich nicht, wenn zusätzlich zum auswaschungsgefährdeten Oberboden auch der Unterboden (bis 70 cm) berücksichtigt wird. Um Unterboden ist die Beziehung zwischen C- und N-Vorrat deutlich schwächer als im Oberboden

Überprüfung der Heißwasserextraktion zur präzisierten Bewertung der Humusversorgung humusarmer Sandböden

Untersuchungen an zwei Dauerdüngungsversuchen in Groß Kreutz (Brandenburg) bestätigen, dass es bei der Bewertung des Humuszustandes nach DirektZahlVerpflV im Rahmen von Cross Compliance zu erheblichen Fehleinschätzungen kommen kann. Unter den Standortbedingungen in Groß Kreutz (trockene Sandböden mit < 6% Ton) haben sich langfristig selbst bei optimaler Bewirtschaftung Corg - Gehalte von nur 0,59 - 0,15% eingestellt. Diese liegen weder eindeutig über dem nach DirektZahlVerpflV geforderten Mindestgehalt von 0,58% Corg, noch ist eine klare Abgrenzung zu suboptimaler Bewirtschaftung möglich. Durch die Bestimmung der heißwasserextrahierbaren C - Gehalte (Chwe) war eine präzisere Bewertung nicht möglich

Iron isotope fractionation in soil and graminaceous crops after 100 years of liming in the long‐term agricultural experimental site at Berlin‐Dahlem, Germany

Sustainable arable cropping relies on repeated liming. Yet, the associated increase in soil pH can reduce the availability of iron (Fe) to plants. We hypothesized that repeated liming, but not pedogenic processes such as lessivage (i.e., translocation of clay particles), alters the Fe cycle in Luvisol soil, thereby affecting Fe isotope composition in soils and crops. Hence, we analysed Fe concentrations and isotope compositions in soil profiles and winter rye from the long-term agricultural experimental site in Berlin-Dahlem, Germany, where a controlled liming trial with three field replicates per treatment has been conducted on Albic Luvisols since 1923. Heterogeneity in subsoil was observed at this site for Fe concentration but not for Fe isotope composition. Lessivage had not affected Fe isotope composition in the soil profiles. The results also showed that almost 100 years of liming lowered the concentration of the HCl-extractable Fe that was potentially available for plant uptake in the surface soil (0–15 cm) from 1.03 (standard error (SE) 0.03) to 0.94 (SE 0.01) g kg−1. This HCl-extractable Fe pool contained isotopically lighter Fe (δ56Fe = −0.05 to −0.29‰) than the bulk soil (δ56Fe = −0.08 to 0.08‰). However, its Fe isotope composition was not altered by the long-term lime application. Liming resulted in relatively lower Fe concentrations in the roots of winter rye. In addition, liming led to a heavier Fe isotope composition of the whole plants compared with those grown in the non-limed plots (δ56FeWholePlant_ + Lime = −0.12‰, SE 0.03 vs. δ56FeWholePlant_-Lime = −0.21‰, SE 0.01). This suggests that the elevated soil pH (increased by one unit due to liming) promoted the Fe uptake strategy through complexation of Fe(III) from the rhizosphere, which favoured heavier Fe isotopes. Overall, the present study showed that liming and a related increase in pH did not affect the Fe isotope compositions of the soil, but may influence the Fe isotope composition of plants grown in the soil if they alter their Fe uptake strategy upon the change of Fe availability.Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/50110000234

Assessing Cumulative Effects of Irrigation on Iron Isotope Fractionation and Mobilization in Arable Soil in Germany

Iron is one of the most abundant elements in soil and analysis of iron isotopes can be a powerful tool to elucidate the biogeochemical cycle of Fe in nature. Over the last two decades, studies of stable isotope variations of Fe have markedly increased, as there are multiple pedogenic processes which induce iron fractionation like continental weathering including dissolution, precipitation, biological processes and redox transformations. Up to date, there is only a limited number of studies that have investigated iron isotope fractionation in soil and, except for one study on a paddy field, none of them are related to agriculture soils. We present first-time data of the stable iron isotope compositions in different depths (down to 100 cm) of agricultural fields. Under long-term irrigation we detected a depletion of light Fe isotopes in deeper soil horizons. By comparison, the non-irrigated plots displayed a relatively uniform isotope composition across all depths. After 50 years of irrigation, significant Fe losses could be detected in the irrigated plots. The Fe isotopes composition of the plant available Fe is also investigated. In all investigated layers, the irrigated plots displayed a greater plant available fraction (9 - 23 % total Fe) than their non-irrigated counter-parts (8 – 17 % total Fe). We will compare the isotope composition of plant available Fe to that of the strategy II plant Triticum aestivum L. grown on this field. We will hence present a comprehensive overview of the Fe isotope fractionation in a lomg-term irrigated agricultural soil-plant system

Applying stable isotope analysis to evaluate soil management techniques in agricultural field sites

An increasing number of studies demonstrate the potential of using non-traditional stable isotopes as a tool to identify soil formation processes, to pinpoint translocation processes or to determine geologic sources, however, these ratios are rarely applied to agricultural systems to assess the impact of agricultural practices on nutrient cycling in soils. Studies show that the isotope composition of several nutrient elements may vary between top- and subsoil due to biogeochemical processes (1, 2). Agricultural soil management may alternate these variations in isotope composition, potentially leading to different isotope signatures in crop tissues due to nutrient uptake. In this study, we present for the first time Mg isotope compositions in soil profiles (down to 100 cm) from a long-term field trial (> 90 years) in Berlin-Dahlem, Germany. The effect of long-term liming was assessed by analysing the isotope compositions of Mg pools in soil and plants. The soil δ26Mg values increased along the soil profile, showing a depletion of heavier Mg in the topsoil and an enrichment of heavier Mg in the subsoil. Magnesium in the non-limed fields was found to be isotopically lighter than that in the limed plots across all depths. Thus, the isotope signature could potentially yield significant information on elemental transports in soils and help to clarify important nutrient uptake processes by crops. In another long-term field trial in Berlin-Thyrow, where irrigation practices have been applied over 50 years, we detected a depletion of light Fe isotopes in deeper soil horizons, while the plough horizons showed an enrichment in light Fe isotopes. By comparison, the non-irrigated plots displayed a relatively uniform isotope composition across all depths. These two studies confirmed that long-term agricultural practices can impact isotope composition of nutrient elements

Non-traditional stable isotope analysis to assess the impact of agricultural soil management techniques on nutrient cycles

An increasing number of studies demonstrate the potential of using non-traditional stable isotopes as a tool to identify soil formation processes, to pinpoint translocation processes or to determine geologic sources, however, these ratios are rarely applied to agricultural systems to assess the impact of agricultural practices on nutrient cycling in soils. Studies show that the isotope composition of several nutrient elements may vary between top- and subsoil due to biogeochemical processes (1, 2). Agricultural soil management may alternate these variations in isotope composition, potentially leading to different isotope signatures in crop tissues due to nutrient uptake. In this study, we present for the first time Mg isotope compositions in soil profiles (down to 100 cm) from a long-term field trial (> 90 years) in Berlin-Dahlem, Germany. The effect of long-term liming was assessed by analysing the isotope compositions of Mg pools in soil and plants. The soil δ26Mg values increased along the soil profile, showing a depletion of heavier Mg in the topsoil and an enrichment of heavier Mg in the subsoil. Magnesium in the non-limed fields was found to be isotopically lighter than that in the limed plots across all depths. Thus, the isotope signature could potentially yield significant information on elemental transports in soils and help to clarify important nutrient uptake processes by crops. In another long-term field trial in Berlin-Thyrow, where irrigation practices have been applied over 50 years, we detected a depletion of light Fe isotopes in deeper soil horizons, while the plough horizons showed an enrichment in light Fe isotopes. By comparison, the non-irrigated plots displayed a relatively uniform isotope composition across all depths. These two studies confirmed that long-term agricultural practices can impact isotope composition of nutrient elements. References:(1) Fekiacova Z., Pichat S., Cornu S., Balesdent J., 2013. Geoderma 209-210, 110-118.(2) Bolou-Bi E.B., Vigier N., Poszwa A., Boudot J.-P., Dambrine E., 2012. Geochimica et Cosmochimica Acta 87, 341–355