Environmental factors determining weed species distribution in organic manure and inorganic fertiliser smallholder maize (Zea mays L.) production

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AbstractWeeds are a major concern in crop production, and their environmental plasticity hinders successful control. A phytosociological study assessed weed distribution patterns in smallholder maize (Zea mays L.) production under different climatic and soil factors in the 2020/2021 and 2021/2022 cropping seasons. Thirty‐six maize fields from the Highveld (Mankayane) and the Middleveld (Luve) of Eswatini, were investigated with three fertiliser regimes applied (cattle manure only, cattle manure plus inorganic fertiliser and inorganic fertiliser only). Phytosociological attributes of weed species including density were collected using a 25 m transect placed horizontally at the centre of each field. Climatic factors and soil physiochemical properties considered included altitude, rainfall, temperature, soil texture, soil pH, nitrogen, phosphorus, potassium, calcium, magnesium, copper, iron, zinc and manganese. Fifty‐six weed species belonging to 16 families were recorded. Distance‐based multivariate multiple regression (DistLM) analysis was used to determine the relationship between weed species composition as the dependent variable from the fertiliser regimes and the environmental factors as the independent variable. Eight environmental variables explained 25% variation in species distribution namely; altitude, temperature, nitrogen, phosphorus, potassium, copper, magnesium and percentage silt. At Luve, temperature, copper and magnesium significantly explained weed distribution in all three fertiliser regimes, while phosphorus influenced weed distribution in the manure only regime. At Mankayane, nitrogen affected weed distribution in the manure plus inorganic fertiliser and inorganic fertiliser regimes whereas altitude, phosphorus, potassium, and %silt influenced weed distribution in the manure only and manure plus inorganic fertiliser regimes. The observations suggest that some weed species coexist between fertiliser regimes and study areas while others occur in specific environments only.