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Quantifying mineral sources of potassium in agricultural soils

Andrist Rangel, Ylva (2008). Quantifying mineral sources of potassium in agricultural soils. Diss. (sammanfattning/summary) Uppsala : Sveriges lantbruksuniv., Acta Universitatis Agriculturae Sueciae, 1652-6880 ; 2008:53
ISBN 978-91-85913-86-2
[Doctoral thesis]

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Soil potassium (K) reserves are crucial for crop quality and yield in low input agricultural systems. Soils contain varying amounts of K-bearing minerals and differ in their inherent K supply capacity. This thesis presents mineralogical methods for characterising and quantifying different K-bearing phases in soil and compares the results with K determined by common soil K extraction methods using 2 M HCl (KHCl) or aqua regia (KAqReg). The aim was to improve evaluations of potential long-term K supply of soils with different parent materials, particularly in grass/clover leys. Mineralogical budgeting based on X-ray powder diffraction was used to determine K distribution in K-bearing minerals in 20 Swedish and Scottish soils. KHCl and KAqReg were then tested against the concentrations of different mineral K pools and HCl effects on mineralogy were assessed through differential X-ray diffraction. Long-term Swedish cropping systems and soil fertility experiments were used to assess field K balances and long-term trends in exchangeable K (Kex) and KHCl and to estimate soil K delivery capacity. The K distribution between K-feldspar and different phyllosilicates varied significantly among soils, with Scottish soils showing greater variation in total K concentrations and K speciation than Swedish soils. HCl and aqua regia solubilised 1-17% and 4-60% of total K, respectively, depending on soil type and mineralogy, most derived from Fe-bearing di- and trioctahedral phyllosilicates. Conventional and organic cropping systems both demonstrated negative field K balances averaging 20-70 kg ha-1 yr-1 over 18 years, indicating a reliance on soil K delivery. This resulted in significantly decreased Kex and KHCl in two soils. Potassium weathering rates were 35-65 kg ha-1 yr-1 in silty clays and sandy loams, and 8 kg ha-1 yr-1 in loamy sands in insufficiently or non-K fertilised experimental plots. To compensate for net K output at field scale, the KHCl soil pool would have to be totally replenished within 30-300 years, depending on site. Although KHCl is a dynamic pool that is not exhausted until the least soluble K-bearing mineral has dissolved, replenishment rate kinetics ultimately limit K delivery from soil reserves. This demonstrates the significance of considering the size and properties of soil nutrient pools when using element balances to assess cropping system sustainability.

Authors/Creators:Andrist Rangel, Ylva
Title:Quantifying mineral sources of potassium in agricultural soils
Series Name/Journal:Acta Universitatis Agriculturae Sueciae
Year of publishing :2008
Number of Pages:105
ALLI. Andrist-Rangel, Y., Simonsson, M., Andersson, S., Öborn, I & Hillier, S. 2006. Mineralogical budgeting of potassium in soil: A basis for understanding standard measures of reserve potassium. Journal of Plant Nutrition and Soil Science 169, 605-615. II. Andrist-Rangel, Y., Edwards, A.C., Hillier, S. & Öborn, I. 2007. Longterm K dynamics in organic and conventional mixed cropping systems as related to management and soil properties. Agriculture, Ecosystems and Environment 122, 413-426. III. Simonsson, M., Andersson, S., Andrist-Rangel, Y., Hillier, S., Mattsson, L. & Öborn, I. 2007. Potassium release and fixation as a function of fertilizer application rate and soil parent material. Geoderma 140, 188-198. IV. Andrist Rangel, Y., Simonsson, M., Öborn, I & Hillier, S. Sources of HCl-extractable potassium in agricultural soils - insights from full pattern quantitative and differential X-ray powder diffraction. (Manuscript). V. Andrist Rangel, Y., Hillier, S., Öborn, I., Lilly, A., Towers, W., Edwards, A. C. & Paterson, E. Assessing long-term potassium supply in grassland soils: A regional perspective based on quantitative mineralogy and aqua regia-extractable K. (Manuscript).
Place of Publication:Uppsala
ISBN for printed version:978-91-85913-86-2
Publication Type:Doctoral thesis
Full Text Status:Public
Agrovoc terms:potassium, agricultural soils, grassland soils, soil fertility, soil analysis, analytical methods, organic agriculture, weathering, sweden, scotland
Keywords:Potassium, soil, agriculture, field balance, mineralogy, grass, ley, organic farming, weathering, HCl, aqua regia, XRPD, differential XRD, XRF
Permanent URL:
ID Code:1805
Department:(NL, NJ) > Dept. of Soil and Environment
(S) > Dept. of Soil and Environment
Deposited By: Ylva Andrist Rangel
Deposited On:04 Sep 2008 00:00
Metadata Last Modified:02 Dec 2014 10:14

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