Soil fertility maintenance with organic amendments to orange fleshed sweetpotato

Abstract

Smallholders in sub-Saharan Africa traditionally cultivate orange-fleshed sweetpotato without soil fertility management, leading to soil nutrient mining and thereby threatening future food security. We set out to determine the potential of locally-accessible organic amendments and weed biomass management to secure crop nutritional quality and yield while maintaining soil fertility. Orange-fleshed sweet potato was fertilized with sole or co-application of poultry manure, cowpea residue, and inorganic fertilizer, combined with removal or incorporation of biomass residue from the fallow period. Non-amended control represented current farmers practice. Poultry manure fertilization, in sole or co-application with inorganic fertilizer, maintained storage root yield from the first to the second season, averaging 7.7 t ha−1. Conversely, non-amended control decreased storage root yield by 61% from the first to the second season. Poultry manure with weed biomass incorporation maintained total soil C and N at 14.4 g kg−1 and 1.1 g kg−1, respectively, after two growing seasons. Poultry manure co-applied with inorganic fertilizer decreased total C and N by 15% and 14% respectively. The changes in soil total C and N observed in this experiment provide basis to support management recommendations for farmers focusing on locally-sourced organic amendments. Poultry manure is the more reliable organic amendment to maintain sweet potato agricultural performance and soil fertility, with potential to support long-term sweet potato cultivation. The negative effect of inorganic fertilizer on total soil nutrient concentration after two seasons needs consideration to avoid soil fertility mismanagement.