Abstract

In order to compare sampling methods for estimating the populations of the seed bank and the populations of weed seedlings during the growing season in the field, an experiment was conducted in the research field of the Agriculture college of Karaj in the cropping year of 2007. In this experiment, sampling of the seed bank was carried out first at the start of the growing season. Then, during the growing season, the weed populations were sampled in 96 points using the networking method, and their means were considered as the base and the real means of the populations of the weeds. Next, to compare other methods with the networking method, sampling was carried out using the systematic, the diagonal, and the random methods, and then the variance of error of each method was calculated and compared with that of the networking method in the format of factorial using a completely randomized design. The first factor studied, the species of weeds, included the three species of grasses, Amaranthus, and Portulaca. The zigzag, the diagonal, and the random sampling methods constituted the second factor. Results relating to the seed bank and those concerning the populations of the weeds were different from each other. The results obtained showed that the suitable method for each species differed according to the different distribution patterns of the weed species in the field. In the seed bank, there were no significant differences among sampling methods for any of the species, but the random method for grasses and Portulaca showed the least error in predicting weed populations. Altogether, among the sampling methods used for Amaranthus, there were no differences in accuracy. Concerning the populations of weed seedlings, the random method for broadleaf weeds (Amaranthus and Portulaca), and the zigzag method for grasses, were the best. As for the seed bank, the variance of error of all the methods decreased with an increase in the number of samples taken; and when more than 15 samples were taken, this trend of decrease in the variance of error stabilized and no more reduction in  error was observed. Regarding the populations of the weeds, no trend was found between the number of samples taken and the variance of error.

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