Is the use of commercial organic ameliorants for cropping justified?

Abstract

Large areas of soils in sub-Saharan Africa are poor in organic matter and nitrogen-phosphorus-potassium (NPK) fertilisation is essential for cropping. Most farmers are smallholders who cannot afford NPK fertilisers but they could consider alternatives like commercial organic ameliorants.This applies also for commercial farmers to improve profitability. The effects of nine ameliorants on the grain yield, biomass yield and harvest index of maize were evaluated over three years at Bothaville (8% clay), Ottosdal (12% clay) and Potchefstroom (34% clay). All ameliorants were applied as manufacturers prescribe. None of the ameliorants can serve as replacement of NPK fertilisers. Active ingredients other than the small amounts of N, P and K they contain, comprised of effective microorganisms (EMs), human manure, humic acids and poultry manure, and were not able to boost crop growth as manufacturers advocated. Biozone (EMs), Gliogrow (EMs), Growmax (Human manure), K-humate (Humic acid) and Crop Care (Humic acid) that were applied with NPK fertilisation resulted in 22 to 44% instances in significantly higher grain yield (938 to 1 288 kg ha−1) compared to the NPK control; however, many inconsistencies between experimental sites and years were observed. The use of commercial organic ameliorants cannot recommended to farmers without proper evaluation.