The influence of soil moisture on weed species composition and diversity in flood recession farming in the Okavango Delta, Botswana

Abstract

Soil moisture influences the composition and diversity of weed species, as well as the competitive dynamics between crops and weeds. The purpose of this study was to determine how soil moisture shape weed community structure in flood recession farming systems. Vegetation sampling was conducted in 17 fields using 1 m² quadrats along gradient-oriented transects, and soil samples were collected at the upper and lower slopes of each field across the 2 cropping seasons at depth of 15 cm, 30 cm, 45 cm and 60 cm, each field had 4 composite samples per cropping season giving a total of 136 composite samples. Statistical analyses, including Kruskal–Wallis, hierarchical cluster analysis, indicator species analysis, multi-response permutation procedures, and Canonical Correspondence Analysis, were employed to evaluate weed distribution and their relationship with environmental variables. The findings showed statistically significant differences (p < 0.05) in soil moisture distribution across the various zones, with distinct weed communities corresponding to specific moisture levels. Species such as Cenchrus biflorus and Tricholaena monachne were more abundant in well-irrigated areas, while Boerhavia coccinea and Portulaca oleracea thrived by accessing moisture near the surface at a depth of 15 cm. In contrast, deep-rooted weeds like Sida cordifolia and drought-resistant species such as Panicum repens favored deeper soil moisture found at 45 cm and beyond. These results emphasise the critical role of soil moisture in shaping weed community composition, affecting both species competition and ecological adaptation within cropping systems. The study highlights the need for effective moisture management to enhance weed control and support sustainable agricultural productivity.