A Quantitative Analysis of the Weed Flora on Arable Land

Singh, B; Chalam, G

A quantitative analysis of the weedflora on arable land is made in experimental plots of 5 sq. m. each, consisting of nineteen samples selected at random from a field with a history of uniform crop production. Altogether ninety-five quadrats were examined and the frequencies (n occurrences) for the twelve weed species are recorded. The number of plants of Cyperus rotundus and Cynodon dactylon were determined by counting the number of rhizomes and the root stocks respectively. The data are plotted and compared with Poisson distribution, the agreement between observed and calculated values being tested by the |chi2 test. The relative variance V/m is estimated for the different species, and this shows a tendency to over-dispersion in all. The maximum over-dispersion (patchiness) is found in the two species with high mean values, i.e. Cyperus rotundus and Chenopodium album. On the other hand, species with low mean frequencies, i.e. all the rare species, are distributed in good agreement with the calculated Poisson distributon, or in other words, their distribution is not distinguishable from random dispersion. Thus the nature of distribution of weed species on arable land is found to be dependent on the mean density of the species and on the mode of reproduction. Individuals with high mean density and vegetative modes of reproduction are not distributed at random.

A Quantitative Analysis of the Weed Flora on Arable Land

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