Hidden miners the roles of cover crops and soil microorganisms in phosphorus cycling through agroecosystems

Background Phosphorus (P) is a limiting nutrient in many agroecosystems and costly fertilizer inputs can cause negative environmental impacts. Cover crops constitute a promising management option for sustainable intensification of agriculture. However, their interactions with the soil microbial community, which is a key driver of P cycling, and their effects on the following crop, have not yet been systematically assessed. Scope We conducted a meta-analysis of published field studies on cover crops and P cycling, focusing on plant-microbe interactions. Conclusions We describe several distinct, simultaneous mechanisms of P benefits for the main crop. Decomposition dynamics, governed by P concentration, are critical for the transfer of P from cover crop residues to the main crop. Cover crops may enhance the soil microbial community by providing a legacy of increased mycorrhizal abundance, microbial biomass P, and phosphatase activity. Cover crops are generally most effective in systems low in available P, and may access unavailable P pools. However, their effects on P availability are difficult to detect by standard soil P tests, except for increases after the use of Lupinus sp. Agricultural management (i.e. cover crop species selection, tillage, fertilization) can improve cover crop effects. In summary, cover cropping has the potential to tighten nutrient cycling in agricultural systems under different conditions, increasing crop P nutrition and yield

Can soil improving cropping systems reduce the loss of soil biodiversity within agricultural soils?

Soil biodiversity, including abundance and function of species living in the soils are important aspects of soil health, and acknowledges that soil is a living ecosystem. The decline of soil biodiversity can lead to a simplification of the soil food web and the inter-relationships as a result of poor soil management. The impact of agricultural management has been shown to reduce diversity, with damaging consequences for nutrient cycling, soil structure and potentially crop yields. However, research is often siloed and the effect of soil biodiversity on crop yields is overlooked by soil ecologists focusing on other ecosystem services; and the role of soil biodiversity on maintaining soil quality and improving crop yields is missed by agronomy researchers. Introducing specific soil improving cropping systems (SICS) have previously been considered as a method to combat soil threats (such as soil erosion or compaction) but have been overlooked as a method of reducing soil biodiversity losses within agriculture. As soil biodiversity loss is interlinked with these other soil threats, SICS will also potentially reduce the impact of them. Here, we review the range of SICS that can be utilised to reduce the threat of soil biodiversity loss, evaluating the effect of SICS on biodiversity across a wide range of organismal groups and consider the impact this will have on the sustainability of agricultural management. There are examples of measures and practices that combine high crop yields with the promotion of soil biodiversity. Selecting specific cropping systems designed to maintain or increase soil biodiversity (e.g., cover crops), promoting the stabilisation of the soil environment (minimum tillage), reducing chemical amendments (targeted spraying and biocontrol), or increasing biological amendments (adding organic matter) are all potential SICS that can be utilised

Rhizosphere Organic Anions Play a Minor Role in Improving Crop Species' Ability to Take Up Residual Phosphorus (P) in Agricultural Soils Low in P Availability

Many arable lands have accumulated large reserves of residual phosphorus (P) and a relatively large proportion of soil P is less available for uptake by plants. Root released organic anions are widely documented as a key physiological strategy to enhance P availability, while limited information has been generated on the contribution of rhizosphere organic anions to P utilization by crops grown in agricultural soils that are low in available P and high in extractable Ca, Al, and Fe. We studied the role of rhizosphere organic anions in P uptake from residual P in four common crops Triticum aestivum, Avena sativa, Solanum tuberosum, and Brassica napus in low- and high-P availability agricultural soils from long-term fertilization field trials in a mini-rhizotron experiment with four replications. Malate was generally the dominant organic anion. More rhizosphere citrate was detected in low P soils than in high P soil. B. napus showed 74–103% increase of malate in low P loam, compared with clay loam. A. sativa had the greatest rhizosphere citrate concentration in all soils (5.3–15.2 μmol g−1 root DW). A. sativa also showed the highest level of root colonization by arbuscular mycorrhizal fungi (AMF; 36 and 40%), the greatest root mass ratio (0.51 and 0.66) in the low-P clay loam and loam respectively, and the greatest total P uptake (5.92 mg P/mini-rhizotron) in the low-P loam. B. napus had 15–44% more rhizosphere acid phosphatase (APase) activity, ~0.1–0.4 units lower rhizosphere pH than other species, the greatest increase in rhizosphere water-soluble P in the low-P soils, and the greatest total P uptake in the low-P clay loam. Shoot P content was mainly explained by rhizosphere APase activity, water-soluble P and pH within low P soils across species. Within species, P uptake was mainly linked to rhizosphere water soluble P, APase, and pH in low P soils. The effects of rhizosphere organic anions varied among species and they appeared to play minor roles in improving P availability and uptake

Soil-Improving Cropping Systems for Sustainable and Profitable Farming in Europe

Soils form the basis for agricultural production and other ecosystem services, and soil management should aim at improving their quality and resilience. Within the SoilCare project, the concept of soil-improving cropping systems (SICS) was developed as a holistic approach to facilitate the adoption of soil management that is sustainable and profitable. SICS selected with stakeholders were monitored and evaluated for environmental, sociocultural, and economic effects to determine profitability and sustainability. Monitoring results were upscaled to European level using modelling and Europe-wide data, and a mapping tool was developed to assist in selection of appropriate SICS across Europe. Furthermore, biophysical, sociocultural, economic, and policy reasons for (non)adoption were studied. Results at the plot/farm scale showed a small positive impact of SICS on environment and soil, no effect on sustainability, and small negative impacts on economic and sociocultural dimensions. Modelling showed that different SICS had different impacts across Europe-indicating the importance of understanding local dynamics in Europe-wide assessments. Work on adoption of SICS confirmed the role economic considerations play in the uptake of SICS, but also highlighted social factors such as trust. The project's results underlined the need for policies that support and enable a transition to more sustainable agricultural practices in a coherent way

Soil-Improving Cropping Systems for Sustainable and Profitable Farming in Europe

Soils form the basis for agricultural production and other ecosystem services, and soil management should aim at improving their quality and resilience. Within the SoilCare project, the concept of soil-improving cropping systems (SICS) was developed as a holistic approach to facilitate the adoption of soil management that is sustainable and profitable. SICS selected with stakeholders were monitored and evaluated for environmental, sociocultural, and economic effects to determine profitability and sustainability. Monitoring results were upscaled to European level using modelling and Europe-wide data, and a mapping tool was developed to assist in selection of appropriate SICS across Europe. Furthermore, biophysical, sociocultural, economic, and policy reasons for (non)adoption were studied. Results at the plot/farm scale showed a small positive impact of SICS on environment and soil, no effect on sustainability, and small negative impacts on economic and sociocultural dimensions. Modelling showed that different SICS had different impacts across Europe—indicating the importance of understanding local dynamics in Europe-wide assessments. Work on adoption of SICS confirmed the role economic considerations play in the uptake of SICS, but also highlighted social factors such as trust. The project’s results underlined the need for policies that support and enable a transition to more sustainable agricultural practices in a coherent way

Soil microorganisms as hidden miners of phosphorus in soils under different cover crop and tillage treatments

Phosphorus (P) is one of the most limiting plant nutrients for agricultural production. The soil microbial community plays a key role in nutrient cycling, affecting access of roots to P, as well as mobilization and mineralization of organic P (Porg). This thesis aimed to better understand the potential of cover crops to enhance plant-soil-microbe interactions to improve the availability of P. This dissertation consists of a meta-analysis of and two field experiments. The used methods showed that microbial P, the activity of P-cycling enzymes and PLFAs increased under cover crops, indicating an enhanced potential for organic P cycling. Gram- positive and Gram-negative bacteria, and to a lesser extent also arbuscular mycorrhizal fungi, increased their abundance with cover crops. However, saprotrophic fungi could benefit most from the substrate input derived from cover crop roots or litter. Enzyme-stable Porg shifted towards pools of a greater lability in the active soil compartments (rhizosheath and detritusphere). The effects of agricultural management, such as cover crop species choice and tillage, were detectable, but weaker compared to the effect of the presence of cover crops. With the obtained results, the research aims of this thesis could be successfully addressed. We were able to confirm that cover crops have the potential to improve main crops access to P. Furthermore, we presented and discussed three pathways of P benefit. In the plant biomass pathway, P is cycled through cover crop biomass and becomes available for the main crop upon litter decomposition. The microbial enhancement pathway describes how the cover crops interaction with soil microbes increases their abundance and activity, thereby increasing the availability of Porg. Some cover crop species seem to be capable of utilizing a biochemical modification pathway, where changes in the sorption capacity of the soil result in a greater quantity of plant-available phosphate. However, the latter pathway was apparently not important in the crop rotations used in our field experiments. The data also allowed us to characterize ways in which plant-soil-microbe interactions under cover crops affected the relationship of soil microbial functions to the enzymatic availability of Porg pools. Cover crops increased the abundance and activity of microbes, especially fungi, as well as microbial P. This enhancement in P-cycling potential shifted Porg toward pools of greater availability to added enzymes. However, the relation between enzymes and Porg pools is complex and is possibly affected by soil P composition and other site characteristics, indicating the need for further research in this area. Finally, we elucidated how the choice of cover crop species and agricultural management can shift the relative importance of the pathways for the P benefit of the main crop, while site-specific management allows farmers to adapt to local conditions and to optimize the functions of their agroecosystems. In conclusion, our results indicate that the pathways of cover crop derived P benefit take place simultaneously. We confirmed the potential of cover crop biomass for the cycling of P, and we suggest that our observed increases in the availability of soil Porg are related to microbial abundance and activity. The interactions of cover cropping and tillage indicate also that P benefit can be optimized by management decisions. Finally, these new insights into soil phosphorus cycling in agroecosystems have the potential to support further development of more sustainable agricultural systems.Phosphor (P) ist einer der wichtigsten limitierenden Naehrstoffe fuer das Pflanzenwachstum in der Landwirtschaft. Bodenmikroben spielen eine Schluesselrolle in Naehrstoffkreislaeufen, beeinflussen das Wachstum von Pflanzenwurzeln, die Mobilisierung sowie die Mineralisierung von organischem P (Porg) und somit den Zugang zu P. Das Ziel dieser Dissertation war die Einschaetzung des Potentials von Zwischenfruechten zur Verbesserung der Interaktionen im System Pflanze-Boden-Mikroben und einer dadurch moeglichen Steigerung der P-Verfuegbarkeit fuer die Hauptfruechte. Diese Dissertation umfasst drei wissenschaftliche Veroeffentlichungen: Eine Literaturrecherche und Meta-Analyse sowie zwei selbst durchgefuehrte Feldexperimente. Die verwendeten Methoden zeigten, dass Zwischenfruechte den P-Gehalt in der mikrobiellen Biomasse, die Aktivitaet von Phosphatasen und mikrobielle Fettsaeuremarker (PLFAs) erhoehen, was auf ein gesteigertes Umsatzpotential von organischen Phosphorverbindungen hindeutet. Die Abundanz von grampositiven und gramnegativen Bakterien, sowie in geringerem Umfang auch von arbuskulaeren Mykorrhizapilzen, wurde durch Zwischenfruechte erhoeht. Gleichwohl waren saprotrophe Bodenpilze die mikrobielle Gruppe, die am meisten von der Substratzufuhr der Wurzeln und Streu profitieren konnte. Stabiles P wurde in den aktiven Bodenzonen der Rhizosphaere und Detritusphaere in labilere Porg-Pools transformiert. Bewirtschaftungseffekte, wie die Wahl der Zwischenfrucht oder Bodenbearbeitung, waren erkennbar, aber wesentlich schwaecher ausgepraegt als der Zwischenfruchteffekt insgesamt. Unsere Ergebnisse bestaetigen, dass Zwischenfruchtanbau zur Steigerung der P - Verfuegbarkeit fuer die Hauptfrucht fuehren kann. Darueber hinaus konnten wir fuer den P- Vorteil drei grundsaetzliche Wirkungspfade aufzeigen, die in aktiven Bodenraeumen stattfinden. UEber den Wirkungspfad Pflanzenbiomasse wird P aus dem Boden in die Biomasse der Zwischenfrucht aufgenommen und waehrend der Zersetzung der Streu fuer die Hauptfrucht verfuegbar. UEber den Wirkungspfad mikrobielle Verstaerkung steigert die Zwischenfrucht im Wurzelraum die Biomasse und Aktivitaet der mikrobiellen Gemeinschaft, wodurch diese die Verfuegbarkeit von Porg erhoehen kann. Durch den Wirkungspfad biochemische Modifikation scheinen manche Zwischenfruchtarten in der Lage zu sein, ueber Wurzelexsudate die P-Sorption im Boden zu senken und dadurch den Anteil an pflanzenverfuegbarem Phosphat zu erhoehen. Weiterhin ermoeglichen die erhobenen Daten die Diskussion, inwiefern mikrobielle Funktionen und die Mineralisierbarkeit von Porg zusammenhaengen und wie die Interaktionen von Pflanzen beeinflusst werden. Zwischenfruechte steigerten sowohl die Abundanz und Aktivitaet von Mikroben, als auch die Menge an P in der mikrobiellen Biomasse. Diese Potentialsteigerung des P-Kreislaufs steigerte die Verfuegbarkeit des Porg fuer zugefuegte Enzyme. Es muss bedacht werden, dass die Rueckkopplungen zwischen Enzymaktivitaet und verschiedenen Porg-Pools komplex sind. Diese haengen von den lokalen Eigenschaften des Bodens, wie etwa der Zusammensetzung des P-Vorrats, ab und sollten durch zukuenftige Studien geklaert werden. Drittens zeigen unsere Untersuchungen, wie die Wahl der Zwischenfrucht und die der Bewirtschaftung (z.B. Bodenbearbeitung oder Fruchtfolge) die relative Gewichtung der verschiedenen Pfade des P-Vorteils fuer die Hauptfrucht beeinflussen. Standortangepasste Zwischenfruchtsysteme erlauben es Landwirt:innen, die Funktionen ihres Agrooekosystems hinsichtlich der lokalen Bedingungen zu optimieren. Zusammenfassend bestaetigen unsere Ergebnisse, dass der P-Bedarf der Hauptfrucht ueber die Biomasse der Zwischenfrucht gedeckt werden kann und zeigen auf, dass die charakterisierten drei Pfade des P-Vorteils durch Zwischenfruchtanbau parallel stattfinden. Schließlich koennen die hier gewonnenen Erkenntnisse ueber den Phosphorkreislauf, basierend auf der Kombination von bodenmikrobiologischen Methoden mit der Charakterisierung der Labilitaet von Porg, zur zukuenftigen Entwicklung einer nachhaltigeren Landwirtschaft beitragen

Interactions between cover crops and soil microorganisms increase phosphorus availability in conservation agriculture, Plant and Soil

Dataset of research articl

Database_archaeobotanical_USOs

Compilation of plant underground storage organs (USOs) recovered at archaeological sites (all countries, all chronologies)

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