Nature 350, 146 - 148 (14 March 1991); doi:10.1038/350146a0

Amelioration of subsoil acidity by application of a coal-derived calcium fulvate to the soil surface

H. v. H. van der Watt^*, R. O. Barnard^*, I. J. Cronje^†, J. Dekker^†, G. J. B. Croft^* & Maria M. van der Walt^*

^* Department of Soil Science and Plant Nutrition, University of Pretoria, 0002 Pretoria, South Africa
^† Division of Energy Technology, CSIR, PO Box 375, 0001 Pretoria, South Africa

SUBSOIL acidity is a serious problem in many tropical and sub-tropical soils^1–3. The high acidity, low calcium contents and often toxic levels of soluble and/or exchangeable aluminium severely impair plant-root development in these soils^1–3. The relative immobility of surface-applied liming materials limits their ability to reduce subsoil acidity. Recently, the use of gypsum or phosphogyp-sum has been advocated as an alternative to lime^3–7. On the other hand, it is well known that humic substances can mobilize and form complexes with metals in soils^8–11. Here we report that a newly available, coal-derived calcium-fulvate is highly efficient as a carrier of calcium in the soil profile. Moreover, subsoil pH was considerably higher when calcium-fulvate was applied to the soil surface, than when gypsum, calcium-EDTA, Ca(OH)² or CaCO³ were applied.

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