WEED DIVERSITY AND SEED BANK STUDIES IN DIFFERENT AGRICULTURE FIELDS IN SOME AREAS OF BHAKTAPUR DISTRICT

Abstract

Weeds in agricultural fields reduces crop yields by competating in nutrients, sunlight, and moisture, among other things.Weeds have the ability to produce a huge number of seeds, and propagate rapidly in agricultural fields due to presence of congenial environment and ultimately reduces crop yield. The weeds present in different fields may be different due to agricultural practices and crops grown there. The aim of present study was to compare the weed diversity in different agricultural fields having cultivation of wheat, cabage and potato. Besides this the aim of this study was also to find out differences in seed bank at different agriculture fields of Bhaktapur. To understand this five different sites (Sudal, Wonti, Chitapole, Gundu, and Jhaukhel) of Bhaktapur district were selected as theses places were having similar crops and agricultural practices. From each sites potato, cabbage and wheat fields were selected for weed diversity and seed bank study in January to Februrary of the year 2020 and 2021. The study of weed diversity was conducted using quadrats of 2×2m2 in both years whereas the study of seed bank was conducted only in 2021. For seed bank study, soil samples from each field was collected using composite sampling, then the seed germination was observed in the collected soil samples by spreading it on plastic plate along with regular watering after 2nd weeks from February 16 th to March 27th 2021. Altogether 49 weed species belonging to 16 families were found in three different agriculture fields. Among them 47 were found in first year and 49 were found in second year. Asteraceae (16) was the dominant family followed by poaceae (8). Poa annua, Soliva anthemifolia, Stellaria media, Chenopodium album, Persicaria hydropiper were the most dominant species as their IVI and weed density/m2 were high in most of the sites except Jhaukhel. Spergula arvensis scored highest IVI and highest weed density/m2 in wheat field of Jhaukhel. The weed density in agriculture fields were increased in second year in compare to first year. From the seed bank study, altogether 1023 seeds of 37 weed species belonging to 15 families were recorded in soil. The dominant families in soil seed bank were Poaceae, Asteracea and Caryophyllaceae. The most abundant species recorded in soil seed bank were Poa annua, Stellaria media, Soliva anthemifolia. Emergence of Cynodon dactylon, Poa annua, Stellaria uliginosa and Persicaria hydropiper were not significantly different at P=0.05 in all selected sites in potato field. Emergence of common weeds Poa annua, Soliva anthemifolia, Stellaria media, Chenopodium album, Persicaria hydropiper were significantly different at P=0.05 in all selected sites in cabbage field and wheat field. Weed seed density of three different agriculture fields in selected sites were insignificantly different. Weed species diversity was high in Gundu whereas it was low in wheat and potato fields of Jhaukhel. But high weed diversity was recorded at cabbage fields of Jhaukhel and low diversity was found in cabbage fields of Wonti. Weed seed bank diversity was high in Gundu and low in Wonti. The similariy index of weeds in agriculture fields and soil seed bank is high in cabbage field of Chitapole and low in wheat field of Jhaukhel. Species richness of soil seed bank followed the same pattern as in fields, with the highest richness in Gundu and lowest richness in Wonti. From both field studies and seed bank study by germination method, weed species richness was found to be high at wheat field and low at cabbage fields. The Shannon diversity index was found to be higher in seed banks than in agricultural field weeds, indicating the importance of seeds in the soil as a reservoir of biodiversity. The similarity index of weeds in cabbage fields and soil seed bank were foud to be highest (86.96%). Some of the weeds like Rorripa palustris, and Amaranthus spinosus, of which A. spinosus is an invasive species, were recorded in the soil seed bank study only but were not found in field study. This finding indicated the possibilities of invasive weed infestation in the agriculture field in future. From this it is evident that the study of a weed seed bank is important as it provided more information about the weed seed infestations at present and also warns us for the future as well.