Plant induced weathering of minerals in the subsoil - release of 'non-exchangeable' potassium from 2:1 layer minerals (TransMinK)
Final Report Abstract
We successfully investigated the role of soil solution concentrations of different cations for the release of interlayer K from 2:1 minerals. The compartment system approach combined with soil solution sampling and the mineralogical analyses was very well suited to answer the initial questions. It could be shown that within 49 and 98 days, respectively, 6.4 and 14.4 % of the illite’s total K was released upon contact with the root system. Together with SP8 we were also able to demonstrate with the compartment system approach that 15N enrichment in plant tissue was significantly lower in treatments with K+ application compared to those without. This was in line with smaller depletion of non‐exchangeable 15NH4+ ‐N in the rhizosphere for these treatments and also with lower 15N abundance in soil solution NO3‐ ‐N fraction. Hence, K+ application hampered the release of NH4+ from interlayers. Also we conducted with the compartment system approach an experiment to proof the reciprocal effect of NH4+ on the release of K+. Plant K status (shoot) was increased by foliar application of KNO3 but no difference was found in root tissue. K depletion in the rhizosphere soil solution was similar whether plants received NH4NO3 or KNO3 as foliar application. Foliar application of nutrients (NH4NO3; KNO3) did neither directly increase soil solution concentration of the respective nutrient nor indirectly affect the concentration of other nutrients by cation exchange. Surprisingly, foliar application of nitrate salts induced a strong increase in rhizosphere pH. In a test with illite, buried in the research group´s Central Field Trial at Klein‐Altendorf in the mineral bags, we got no results visible by X‐ray diffraction after being exposed in the field for 3 months. Root growth into biopores could be investigated with undisturbed soil columns from the subsoil (Luvisol Klein‐Altendorf) by X‐ray micro CT and the pore‐ and root systems could be analysed and partly quantified. In addition pore profiles extending from the pore wall into the bulk soil were chemically analysed. For Ct, Nt, and Pt there is a trend of decreasing concentrations with increasing distance from the pore surface which is in line with literature and for P was also confirmed by SP7 in the first phase. Rhizosphere soil is showing no difference from bulk soil. For K no gradient is found for the exchangeable fraction but for ‘non‐exchangeable’ and total K a clear increase with increasing distance from the pore surface was found. Surprisingly very marked gradients were also found for total concentrations of Al, Fe, Mg, which are lower at the wall surface and increase towards the bulk soil, and for Si, Ca and Mn, which show the opposite trends, i.e. decreasing concentrations with increasing distance from the wall surface. Most results have been published in peer‐reviewed journals relevant for the community. The next step, addressing spatial heterogeneity of root growth, spatial distribution of K and soil structure was supposed to be addressed in the second phase of the research group. This was not successful, although the technology would be available (X‐ray CT, undisturbed soil sampling, small scale soil solution sampling) for addressing this topic and recent publications show that it would be very timely to address root growth and function in structured soil.
Publications
-
(2013): Illite transformation and potassium release upon changes in composition of the rhizosphere soil solution. Plant Soil 371 (1‐2), 267 – 279
Vetterlein, D., Kühn, T., Kaiser, K., Jahn, R.
-
(2013): Nutrient acquisition from arable subsoils in temperate climates: a review. Soil Biol. Biochem. 57 , 1003 – 1022
Kautz, T., Amelung, W., Ewert, F., Gaiser, T., Horn, R., Jahn, R., Javaux, M., Kemna, A., Kuzyakov, Y., Munch, J.C., Pätzold, S., Peth, S., Scherer, H.W., Schloter, M., Schneider, H., Vanderborght, J., Vetterlein, D., Walter, A., Wiesenberg, G.L., Köpke, U.
-
(2014): Contribution of anecic earthworms to biopore formation during cultivation of perennial ley crops. Pedobiologia 57 , 47 – 52
Kautz, T., Lüsebrink, M., Pätzold, S., Vetterlein, D., Pude, R., Athmann, M., Küpper, P.M., Perkons, U., Köpke, U.
-
(2015): Impact of potassium on plant uptake of non‐exchangeable NH4+ ‐N. Plant Soil 387 (1‐2), 37 – 47
Beuters, P., Scherer, H.W., Spott, O., Vetterlein, D.
