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Effect of Trees on Forms of Soil Phosphorus in an Agroforestry Parkland in Burkina Faso
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Gerhard Gröbner)ORCID iD: 0000-0001-9395-5030
Burkina Faso.
Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics. (Jurgen Schleucher)
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Gerhard Gröbner)
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2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Phosphorus is commonly a limiting nutrient for crop production, especially in highly weathered tropical soils. In two semi-arid areas in Burkina Faso with high and low aluminum and iron content respectively, we studied the effect of scattered trees within cropping fields (an agroforestry system called “parklands”) on soils from two areas with high and low aluminum and iron content, respectively. The study focused on different P forms using liquid-state 31P NMR, and their relation to soil chemical properties, determined by XRF. We hypothesized that i) There is generally a difference in P forms between under canopies and in openings outside canopies due to higher input and turnover of organic material close to trees; ii) Close to trees there are more P forms of microbial origin due to the increased activity of the microbial community; iii) This difference is more pronounced in the area with higher content of aluminum and iron. We took topsoil samples under tree canopies as well as outside tree canopies. Our results showed that there were generally low levels of organic carbon and P, but under the canopies of the scattered trees the levels were higher. 31P-NMR showed that soil P was composed of similar ratios of inorganic and organic P as has been observed in other ecosystems, and that the organic P pool was composed of P species commonly observed in soils. NMR also revealed that areas outside the canopies had a less diverse P composition. In the area with high Al/Fe content, microbial activity under trees had a more pronounced effect on the soil P composition, by significantly increasing the amounts of P species of biological origin. In conclusion, the study confirmed the importance of soil organic matter and trees for P availability in semi-arid tropical ecosystems.

Place, publisher, year, edition, pages
2014. , 58 p.
Keyword [en]
phosphorus, 31P NMR, agroforestry, multivarate, nutrients, sub-sahelian
National Category
Physical Chemistry Geosciences, Multidisciplinary
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-93378ISBN: 978-91-7601-132-4 (print)OAI: oai:DiVA.org:umu-93378DiVA: diva2:748459
Available from: 2014-09-19 Created: 2014-09-18 Last updated: 2014-09-30Bibliographically approved
In thesis
1. Analysis and speciation of organic phosphorus in environmental matrices: Development of methods to improve 31P NMR analysis
Open this publication in new window or tab >>Analysis and speciation of organic phosphorus in environmental matrices: Development of methods to improve 31P NMR analysis
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Phosphorus (P) is an essential element for life on our planet. It is central in numerous biochemical processes in terrestrial and aqueous ecosystems including food production; and it is the primary growth-limiting nutrient in some of the world’s biomes. The main source of P for use as agricultural fertilizer is mining of non-renewable mineral phosphate. In terrestrial ecosystems the main source is soil P, where the largest fraction is organic P, composed of many species with widely differing properties. This fraction controls the utilization of P by plants and microorganisms and influences ecosystem development and productivity. However, there is only scarce knowledge about the molecular composition of the organic P pool, about the processes controlling its bioavailability, and about its changes as soils develop. Therefore, the aim of this thesis was to develop robust solution- and solid-state 31P nuclear magnetic resonance spectroscopy (NMR) methods to provide molecular information about speciation of the organic P pool, and to study its dynamics in boreal and tropical soils. By studying humus soils of a groundwater recharge/discharge productivity gradient in a Fennoscandian boreal forest by solution- and solid-state NMR, it was found that P speciation changed with productivity. In particular, the level of orthophosphate diesters decreased with increasing productivity while mono-esters such as inositol phosphates increased. Because the use of solution NMR on conventional NaOH/EDTA extracts of soils was limited due to severe line broadening caused by the presence of paramagnetic metal ions, a new extraction method was developed and validated. Based on the removal of these paramagnetic impurities by sulfide precipitation, a dramatic decrease in NMR linewidths was obtained, allowing for the first time to apply modern multi-dimensional solution NMR techniques to soil extracts. Identification of individual soil P-species, and tracking changes in the organic P pools during soil development provided information for connecting P-speciation to bioavailability and ecosystem properties. Using this NMR approach we studied the transformation of organic P in humus soils along a chronosequence (7800 years) in Northern Sweden. While total P varied little, the composition of the soil P pool changed particularly among young sites, where also the largest shift in the composition of the plant community and of soil microorganisms was observed. Very old soils, such as found Africa, are thought to strongly adsorb P, limiting plant productivity. I used NMR to study the effect of scattered agroforestry trees on P speciation in two semi-arid tropical woodlands with different soil mineralogy (Burkina Faso). While the total P concentration was low, under the tree canopies higher amounts of P and higher diversity of P-species were found, presumably reflecting higher microbial activity.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2014. 58 p.
Keyword
Phosphorus, soil, 31P NMR, NaOH/EDTA, terrestrial, sulfide, speciation, bioavailability, paramagnetic, humus, boreal, tropical, multi-dimensional, agroforestry, chronosequence
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-93409 (URN)978-91-7601-132-4 (ISBN)
Public defence
2014-10-17, KBC-huset, Stora hörsalen, KB3B1, KBC huset, s-90187, Umeå, 10:00 (English)
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Supervisors
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I delarbete III har titel och författaruppgifter förändrats.

Available from: 2014-09-26 Created: 2014-09-19 Last updated: 2014-09-24Bibliographically approved

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Vestergren, JohanSchleucher, JurgenGröbner, Gerhard

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