Impact of potassium on plant uptake of non-exchangeable NH 4 + -N

• Published in: Plant and soil Vol. 387; no. 1/2; pp. 37 - 47
• Main Authors: Beuters, Patrick, Scherer, Heinrich W., Spott, Oliver, Vetterlein, Doris
• Format: Journal Article
• Language: English
• Published: Springer 01.02.2015
• ISSN: 0032-079X; 1573-5036

Aims and background Release of 'non-exchangeable' NH4+-N from interlayers of 2:1 clay minerals is postulated to depend not only on soil solution NH4+-N concentration but also on the concentration of K+ and Ca2+. Concentrations of all three cations are altered in rhizosphere compared to soil solution at larger distance from the root surface. Methods Non-exchangeable NH4+-N pool was labelled with 15N. Treatments including application of K+, Ca2+ and K+ + Ca2+ were established. In a compartment system approach we analysed changes in soil solution concentrations of 15NH4+-N, 15NO3−-N, K+ and Ca2+ in situ at different distances from the root surface over time and related them to the release of non-exchangeable 15NH4+-N and uptake of 15N by plants. Results and conclusions The 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 the interlayers. A promoting effect of increasing Ca2+ concentrations on release of non-exchangeable NH4+-N could not be evaluated since the Ca2+ concentration in soil solution was largely controlled by small amounts of carbonate contained in the substrate and thus the addition of Ca2+ did not result in a relevant increase of soil solution Ca2+ concentration as originally intended. The use of 15N to follow the fate of non-exchangeable NH4+-N proved very useful as it provides a higher sensitivity for all measured fractions compared to total N. However, as soil N fractions equilibrate with each other labelling one fraction exclusively is not possible.