Evaluation Of The Impact Of A Range Of Soil Ameliorants On Soil Chemical And Biological Properties

Crop yields in southern African sugar industries are frequently limited by unfavourable chemical and biological conditions in soils. In addressing these problems, growers make use of various organic and inorganic products, depending on the nature of the limitation. However, the efficacies of numerous products currently in use remain untested. This investigation involved the evaluation of 12 products in a short-term (8 weeks) pot incubation study using a sandy, acid Cartref topsoil. The organic products included were chicken litter (CL), mushroom compost substrate (SMS), flyash, filterpress, vermicast, liquid CMS (CMS_L), and granular CMS (CMS_G). Inorganic products were the liming agents, dolomitic lime and Calmasil, and gypsum, Langfos, and quarry dust. Short term (3-day) CO2 release, a sensitive indicator of biological activity, increased significantly with the application of the liming agents, filterpress, CL and flyash. Mineral N levels were increased significantly by liming agents, CL and CMS_G. Potassium levels were unaffected by inorganic products but increased with the application of CL and CMS_L. Resin-extractable P levels increased with CL, filterpress and CMS_G; Calmasil, too, increased resin P levels, with this being probably due to the Si in the product promoting P release from soil colloids. Of all the products tested, only lime and Calmasil increased pH significantly. Acid saturation was decreased by liming agents, gypsum and quarry dust, while CMS_G increased acid saturation, probably due to nitrification of the ammoniacal N in the product. It is concluded that short-term incubation studies of this kind provide a useful alternative to more costly field trials for characterising the efficacies and modes of action of various soil ameliorants.