Evaluation of sampling methods and assessment of the sample size to estimate the weed seedbank in soil, taking into account spatial variability

Abstract

Summary As field sampling is time consuming, it is necessary to develop efficient sampling techniques to obtain accurate estimates of the weed seedbank in soil. The relative efficiency between sampling schemes depends on the spatial variability in weed seed density across agricultural fields. Spatial variability of the weed seed density was characterized by theoretical correlograms. A systematic sampling (square grill) scheme was considered and it was found that, taking into account spatial variability, this sampling scheme was more efficient than simple random sampling. As a result, the sample size can be reduced in comparison with that given in previous studies, where spatial correlation was ignored. The reduction depends on the correlation structure defined as a function of the ratio, τ, between the nugget effect and the sill of the variogram. The maximum reduction of the sample size, without loss of either precision or confidence level corresponds to the case where there is no nugget effect, τ = 0. The opposite extreme case, where the reduction is nil, corresponds to the case of a pure nugget effect τ = 1. The abaci based on given expressions are provided to determine the sample size in species whose spatial pattern can be fitted either to a Poisson or to a negative binomial distribution.

Comparing solar radiation interception and use efficiency for the energy crops giant reed (Arundo donax L.) and sweet sorghum (Sorghum bicolor L. Moench)

“…Because our experimental RUE value of 5.74 g M J −1 for giant reed is at the theoretical limit for a C4 canopy, a cautionary remark is appropriate here. The choice of optimal sampling size is fundamental to obtain reliable estimates of variables describing agroecosystem evolutions (Ambrosio et al, 2004). Confalonieri et al (2006) carried out an accurate experiment on rice (Oryza sativa L.) to determine the optimal sample size for rice aboveground biomass estimation.…”

Seed banking in ancient forest species: why total sampled area really matters

“…Most authors agree that the total sampled area -apart from sampling mode, seed count method, etc. Second, sampling mode has also received some attention (Bigwood and Inouye, 1988;Ambrosio et al, 2004;Bossuyt et al, 2007). Bossuyt et al, 2007;Stark et al, 2008) or even more so for seed densities (e.g.…”

Precision of systematic and random sampling in clustered populations: habitat patches and aggregating organisms

“…Cochran ( 1946, see also Iachan 1982 analytically proved that a systematic design is more precise for linear populations whose spatial autocorrelation declines exponentially with separation distance. Examples of systematic designs bringing higher survey precision in spatially autocorrelated populations were reported in a range of applied ecological contexts (e.g., Dunn and Harrison 1993, Ambrosio et al 2004, Aune-Lundberg and Strand 2014 and in the application of Euclidean distance analysis to animal habitat selection analysis (Benson 2013 ) and in stereology (Gundersen et al 1999 ).…”

“…More recent statistical investigation (D ' Orazio 2003, Wolter 2007 ) assumed systematic sampling to be more precise in autocorrelated populations and focused on the still unsolved problem of how to reliably estimate the variance of the estimate of the mean from a systematic survey for linear (Wolter 1984(Wolter , 2007 and two-dimensional (i.e., spatial) populations (D ' Orazio 2003 ). Published studies in the applied ecological literature have now shifted to general agreement that systematic designs are more precise in spatially autocorrelated populations (e.g., Dunn and Harrison 1993, Ambrosio et al 2004, Aune-Lundberg and Strand 2014.…”