Effect of the change of accompanying cation of mineral nitrogen fertilizers on soil physical properties
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Institute of Soil Science, Department of Ecology, Weihenstephan Center of Life and Food Sciences, Technical University of Munich, D-85350 Freising, Germany
Int. Agrophys. 2005, 19(2): 91–97
In 1932, a nitrogen fertilizer trial was initiated on a loamy Oxyaquic Eutrochrept near Munich (Germany). After 45 years, the sodium nitrate plots showed a much stronger slaking of the soil surface compared to the calcium nitrate plots in 1976. Sampling of the experimental plots to 1 m depth in order to determine bulk density, saturated hydraulic conductivity, soil moisture characteristic, slaking resistance and exchangeable cations was only possible after termination of the experiment in 1998. Comparison of the laboratory results of both plots showed increased contents of exchangeable Na, but no decrease of exchangeable Ca for the sodium nitrate plots. Bulk density at depths >50 cm increased and the slaking resistance decreased on those plots. The other soil structural properties determined were not significantly affected. The reason behind these unexpected findings is the change from sodium nitrate to calcium nitrate + cattle salt as the sodium nitrate fertilizer in 1984, 15 years prior to sampling. The resulting additional supply of Ca2+ was able to remediate the formerly visible deterioration of the soil structure by Na+. The adverse structural effects of an unfavourable fertilizer type (based on monovalent cations) can therefore be reversed by a change to a more appropriate type (based on bivalent cations, preferentially Ca2+).