Koch, Maximilian: Phosphorus forms in fertilized arable soil profiles and related 33P uptake. - Bonn, 2019. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5n-55685
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5n-55685,
author = {{Maximilian Koch}},
title = {Phosphorus forms in fertilized arable soil profiles and related 33P uptake},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2019,
month = sep,

note = {Arable soils usually store several thousand kg phosphorus (P) per ha, thus far exceeding the recommended P fertilizer dose to sustain crop yields. However, the soil profile is frequently not considered in fertilizer recommendations, because P supply to the plants from the subsoil is lacking clarification. This thesis is determined by the overarching hypothesis that a large part of the P already present in the soil is neither physically accessible nor chemically available to plants and thus does not contribute to plant nutrition. Therefore, my goal was to evaluate the P bonding forms at different soil depth, and to determine the contribution of these P forms to plant nutrition.
My specific objectives were (i) to characterize and quantify the chemical speciation of P forms in soil profiles of agricultural long-term fertilizer experiments, (ii) to elucidate the supply potentials of moderately bioavailable P pools for plants, and finally (iii) to methodologically refine radiotracer-based digital autoradiography for quantifying spatial and temporal P uptake in plants. For this purpose I sampled (i) soil profiles (0 cm to 90 cm) from two long-term fertilizer experiments located in Rostock (Stagnic Cambisol, > 16 years duration) and Bad Lauchstädt (Haplic Chernozem, > 100 years duration); each experiment was comprised of an unfertilized control, an organic treatment (compost or manure), a mineral treatment (triple superphosphate or superphosphate), and a surplus treatment combining organic and mineral applications. Soil P analyses comprised the assessment of P stocks and speciation of P pools of varying chemical extractability, using sequential fractionation, nuclear magnetic resonance (NMR) as well as X-ray absorption near edge structure (XANES) spectroscopy. To trace P uptake from moderately bioavailable P pools, I (ii) conducted uptake studies including two soil orders; a Haplic Luvisol subsoil, that had never been P fertilized and an Orthic Ferralsol subsoil from Australia from a conventional agricultural background. Investigations were accompanied by digital autoradiography to trace plant uptake of P radiotracers. The experiment was conducted in rhizoboxes with 33P loaded Fe and Al hydroxides in combination with diffusive gradients in thin films (DGT) techniques. The radiotracer method was then (iii) extended by advanced quantitative evaluation of the uptake of P radiotracers in wheat and maize. The 33P quantification was carried out with co-exposed 14C standard references during the imaging process.
The P fertilizer application (i) in excess of plant P demand significantly increased both top- and subsoil P stocks. Intriguingly, there was little if any difference in P stocks and the speciation of P forms for organically and inorganically fertilized plots, suggesting that the kind of fertilizer used had only limited effects on the soil P status in the long term. The P uptake study suggested that (ii) P supply from non-soluble, soil-inherent inorganic P bonding forms can compensate insufficient levels of available P in soil solution. Specifically, in the rhizobox experiments performed, even subsoil P bound to Fe and Al oxidic phases was able to contribute up to 30% of overall uptake of P by young wheat plants. Additionally, DGT applications indicated a better P availability from amorphous Fe hydroxide than from Al hydroxide. The overall P uptake, however, was regulated by soil moisture contents, indicating that water supply to plants controlled P uptake and the final amount of soluble P. These investigations were fundamentally supported by digital autoradiography, whose application resulted (iii) in a successful method for quantification of 33P radiotracers in plant tissues.
In summary, P fertilizer applications control soil P stocks but effects on P speciation are minor. In the arable soil profiles studied here, P was predominantly bound to oxidic soil phases, suggesting that a significant portion of soil P dynamics is mediated by such inorganic P pools of varying availability, whereas organic P pools seem to be equilibrated with the general P status of the soil. The P supply rates from non-soluble, moderately labile P forms, rather than immediate mineralization processes, seem to control the long-term P supply for crops.},

url = {https://hdl.handle.net/20.500.11811/8005}

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