Ecology of Some Weeds of Winter Crop Fields in Kathmandu Valley

Abstract

In Nepal, weeds cause yield loss up to 45% in the mustard (Brassica campestris L.) field and 50% in wheat (Triticum aestivum L.), sometimes even more losses when the weed population and density are higher. Usually, weeds are harmful but some may have economic importance as organic compost, food or fodder, medicine, and industrial uses. The use of invasive plants (like Ageratina adenophora (Spreng) King & Rob. and Parthenium hysterophorus L.) and a native weed (Artemisia dubia Wall. Ex. Besser), for preparing biofertilizer and their effect on weed and winter crops have been investigated in the present study. The main objectives of the present study were to understand the weed ecology in winter crop fields. Other important objectives were to investigate the allelopathic effect of Artemesia dubia, Ageratina adenophora and Parthenium hysterophorus to control selected weeds of winter crops by using aqueous extract, compost extract, and their compost. The study was carried out at the wheat and mustard fields of selected sites (Kirtipur, Bhaktapur, Godawari, Chapagaon, Dharamsthali, and Shivapuri) during winter (Oct-March) in the year 2012-2014. Based on the highest IVI value only four common weed species (Ageratum conyzoides L., Bidens pilosa L., Cyperus rotundus L., and Galinsoga parviflora Cav.) were selected for a further ecological studies like phenology, soil seed bank, seed morphology, seed germination, and allelopathic effect. Altogether 40 plants of each weed (Ageratum conyzoides, Bidens pilosa, Cyperus rotundus, and Galinsoga parviflora) were randomly selected and their phenophase was carefully examined from the germination stage to seed dispersal stage of plants using the phenological index technique. The shape, color, and size (length and breadth) of the four common weed seeds were measured under a compound microscope for weed seed morphology study. Seed germination experiment was conducted on environmental conditions like moisture (content 3, 6, 9, 12, 15 ml), temperature (5, 10, 15, 20 and 25˚C), pH (value 4, 5, 6, 7, 8 and 9) and light (normal, red, yellow, blue, green and dark color). For the crops, optimum moisture content (9 ml) was required. The experiments on seed germination of moisture indicated that Cyperus rotundus and Galinsoga parviflora do not require more moisture to germinate and grow. Seed germination of both crops enhanced significantly at 15 to 20˚C treatments but all weed seeds were significantly high at 10 to 15˚C. The percentage of seed germination of both crops Brassica campestris and Triticum aestivum increased significantly in normal and green light. Seed germination of Ageratum conyzoides, Cyperus rotundus, and Galinsoga parviflora was significantly different in normal, red, yellow, and green light. Germination of all weed seeds was completely inhibited in blue and dark light. Seed germination and seedling growth were higher in pH 5-7 in most cases. Seed germination was also conducted with different concentrations (control, 1, 2.5, 5, 10%) of chemical fertilizer solutions and different doses of fertilizer amended in soil (control, 10, 20, 40, 50 g/kg soil). Seed germination of both crops and all the weeds were mostly high in control and 1% of both urea and potash solution. The germination of selected weed seeds reduced significantly with increasing concentrations of both urea and potash in soil. The aqueous extracts vegetative parts of Ageratina adenophora, Parthenium hysterophorus, and Artemisia dubia, their compost extract (of the whole plant) of different concentration (control, 1, 2.5, 5, and 10%) and soil amended with composts (of different doses 0, 10, 20, 40, and 50 g compost/kg soil) were used to understand their effects on seed germination, seedling growth of crops (Triticum aestivum, Brassica campestris) and the common weed. The aqueous and compost extracts of Ageratina adenophora and Parthenium hysterophorus significantly reduced seed germination and seedling length (shoot and root) with increasing concentrations. The stem and leaf extracts of Ageratina adenophora showed a more inhibitory effect on the seed germination of both winter crops and all weeds as compared to root extract. In the soil amended with different amounts of Ageratina adenophora and Parthenium hysterophorus compost showed more reduction in seed germination among the weeds in comparison to both crop plants. Seed germination of Cyperus rotundus was completely inhibited even at 1% Parthenium compost extract and soil amended with 10 g/kg Parthenium compost. The aqueous extract and compost extracts and compost of the native plant Artemisia also significantly reduced seed germination, seedling length of both selected crops and weeds, with increasing concentrations, but were less detrimental than the compost of the other two invasive weeds. From this study, it was found that compost of Ageratina adenophora and Parthenium hystrophorus at the rate of 20-40 g/kg soil was effective to control the winter weeds. Hence the use of Ageratina adenophora and Parthenium hysterophorus compost are suggested to use at low concentrations (20-40 g/kg soil) in wheat or mustard fields, especially to control most of the common weeds. This information suggests preparing compost from the invasive weeds which can act as environmentally safe and cost-effective bio-herbicides along with an important strategy for weed management.