Composition and diversity of weed flora in paddy fields of Bhaktapur, Nepal

Abstract

Weeds are perception-based plant species, which are considered nuisance, undesirable or useful based on, where it flourishes. Generally, weeds are known for their damage, increasing labor and causing economic loses. The weeds can also possess a lot of use value from biodiversity aspect, ecological aspect, utilitarian benefits as well as using them as herbicides and insecticides. So, enumeration and understanding environmental variables affecting weed composition and diversity is important. The study was carried in Changunarayan Municipality of Bhaktapur District. An approach for enumeration of weeds and its response to environmental variables was studied. A total of 60 quadrats of (1 × 1) m 2 were studied in three different sites which were categorized based on their crop rotation practice as Site A (CRPC), Site B (CRW) and Site C (CRB). The environmental variables used were soil organic matter, soil pH and water level in the field. Weed population and their density were recorded, which were subjected to multivariate analysis. Altogether 32 species of weeds were enumerated that were making up community assemblage in paddy ecosystem, which belong to 27 genera and 14 families. Among the enumerated weeds 20 species found inside paddy fields and 12 species in the levee. Asteraceae, Poaceae and Cyperaceae were most dominant families in the paddy field. Mainly the field were dominated by broad leaved species (dicots) than the narrow leaved species (monocots). The study of IVI showed that Acmella paniculata, Lindernia antipoda, Blyxa aubertii, Cyperus iria, Cyperus difformis and Alternanthera philoxeroides were major dominant species in the paddy fields. The density of weeds in Site A (CRPC), Site B (CRW) and Site C (CRB) was 40, 44 and 85 individuals per square meter respectively. The application of diversified crop rotation in the field change the soil properties, level of fertilizer input and soil organic matter. The diversified crop rotation field experience higher diversity than monoculture or fallow land. The DCA and RDA analysis showed beta diversity was found low and linear relationship in the study. It might be due to habitat homogeneity, management practice or similar climatic conditions. RDA showed preference of specific environmental variables by species, whose manipulation can cause change in composition & diversity of those species. The water level and soil pH had positive correlation to species density. The soil pH, water level, SOM and crop rotation were important environmental variables. They were not acting alone, but the multitude of other variables might be related to weed species composition and their diversity.