Response of weed flora dynamics in organic manuring and inorganic fertilisation in a smallholder crop-livestock system

Abstract Fertiliser input in annual cropping systems can benefit crops and weeds. The effects of organic and inorganic fertilisers on weed species composition were evaluated across two agroecological zones in Eswatini: the Highveld and the Middleveld. Weed field surveys and weed seed bank studies were conducted over two cropping seasons, 2020/2021 and 2021/2022, in fields managed by smallholder farmers practising maize and cattle production. Fertiliser regimes were cattle manure only, cattle manure plus inorganic fertiliser, and inorganic fertiliser only, replicated six times in each region. The weed survey was conducted using three 25-m transects, and the weed seed bank was assessed at sampling depths of 0–10 and 10–20 cm. Results showed that cattle manure only and cattle manure plus inorganic fertiliser regimes had higher species richness and diversity than the inorganic fertiliser only regime. However, weed seed distribution did not differ between sampling depths or fertiliser regimes. Twelve weed species, including bermudagrass, crabgrass, and goosegrass, were key contributors to the differences in species composition between fertiliser regimes and agroecological zones, and were the most prevalent weeds in the seed bank. The study established that fertiliser type influences weed species composition and diversity. Proper cattle manure composting is essential to mitigate weed proliferation and enhance sustainable maize production. These findings demonstrate the need for integrated weed management and fertiliser strategies to improve crop yield and agricultural sustainability for smallholder farmers.