Factors influencing the precision of soil seed bank estimates

Abstract

The dimension of soil augers needed to sample a seed bank of Chenopodium spp. (lamb's-quarters) was determined by randomly sampling a 1.35-ha area within a cornfield in Oxford County, Ontario. Sampling units of three different auger sizes (1.9, 2.7, and 3.3 cm in diameter) were collected. On a per volume basis, there were no significant differences between the three sizes of auger in estimating the number of lamb's-quarters seeds in the soil. Three sampling methods, systematic, stratified random, and cluster, were compared with random sampling in their capacity to minimize the sampling variance. Soil cores of 1.9 cm diameter and 15 cm deep were taken systematically at 3.5-m intervals to form a 32 × 32 matrix. Repeated sampling within the matrix using Monte Carlo techniques indicated that the estimate of sampling variance decreased with increasing sample size, regardless of the sampling method used. No fewer than 60 sampling units should be collected to quantify the seed bank of an abundant weed such as lamb's-quarters. The estimates of sampling variance of systematic and cluster sampling were clearly influenced by the sampling interval and the cluster's shape, respectively. This was attributed to the underlying seed distribution of lamb's-quarters in the soil that was clustered with patterns of high and low seed density parallel to corn rows. There were no significant differences between the estimate of sampling variance of random and stratified random sampling with a fixed sample size of 64 units.

Correlação da distribuição espacial do banco de sementes de plantas daninhas com a fertilidade dos solos

“…Além da época de realização do mapeamento, o tempo disponível para executá-lo em grandes áreas pode ser limitante, pois existem estádios ideais para o controle das plantas daninhas (Cardina et al, 1997), comprometendo a confecção do mapa para tratamento localizado, uma vez que, se o tempo despendido para o mapeamento da infestação for grande, poderá ser tarde para se tomar alguma decisão de controle.…”

“…Quando feito adequadamente, o mapeamento do banco de sementes pode ser utilizado para previsão dos locais de infestações em cultivos posteriores (Cardina et al, 1997).…”

“…No entanto, existe uma grande dificuldade em mapear a flora emergente das plantas daninhas durante o ciclo da cultura, pois sua emergência depende de vários fatores biológicos, ambientais e de manejo. Entre os fatores que interferem na emergência de plantas daninhas, podem-se citar o sistema de produção, o histórico de fertilidade e de manejo de solos, os herbicidas utilizados, a cultura e o clima (Benoit et al, 1989). …”

Weed flora of cassava in west Nile zones of Uganda

“…Weeds grow more vigorously and regenerate more quickly because of the heat and high light intensity (Benoit et al, 2004). High humidity and high temperature that are characteristic of subSaharan Africa, favour rapid and excessive weed growth (Akobundu, 1980).…”

The effect of different soil core samplers on precision of estimating weed seedbank in soil

“…However, along with increasing precision, the estimation becomes more time-consuming and decreases the labour productivity. In order to achieve an adequate precision of estimation, it is necessary to determine the optimum number of samples taken per unit area and/or the volume of the analyzed soil (Barralis et al 1986, Benoit et al 1989, Dessaint et al 1990). The number of replications (cores) does not depend on the size of the examined area, but on the uniformity of its weed infestation (Dvořák 1971).…”