title: Designing a sampling scheme to reveal correlations between weeds and soil properties at multiple spatial scales.
abstract: Weeds tend to aggregate in patches within fields, and there is evidence that this is partly owing to variation in soil properties. Because the processes driving soil heterogeneity operate at various scales, the strength of the relations between soil properties and weed density would also be expected to be scale-dependent. Quantifying these effects of scale on weed patch dynamics is essential to guide the design of discrete sampling protocols for mapping weed distribution. We developed a general method that uses novel within-field nested sampling and residual maximum-likelihood (reml) estimation to explore scale-dependent relations between weeds and soil properties. We validated the method using a case study ofAlopecurus myosuroidesin winter wheat. Using reml, we partitioned the variance and covariance into scale-specific components and estimated the correlations between the weed counts and soil properties at each scale. We used variograms to quantify the spatial structure in the data and to map variables by kriging. Our methodology successfully captured the effect of scale on a number of edaphic drivers of weed patchiness. The overall Pearson correlations betweenA. myosuroidesand soil organic matter and clay content were weak and masked the stronger correlations at >50 m. Knowing how the variance was partitioned across the spatial scales, we optimised the sampling design to focus sampling effort at those scales that contributed most to the total variance. The methods have the potential to guide patch spraying of weeds by identifying areas of the field that are vulnerable to weed establishment.
authors.affiliation: Rothamsted Research Harpenden Hertfordshire UK; School of Agriculture Policy and Development University of Reading Earley Gate Reading UK.
authors.forename: H
authors.initials: H
authors.lastname: Metcalfe
authors.affiliation: Rothamsted Research Harpenden Hertfordshire UK.
authors.forename: A E
authors.initials: AE
authors.lastname: Milne
authors.affiliation: Rothamsted Research Harpenden Hertfordshire UK.
authors.forename: R
authors.initials: R
authors.lastname: Webster
authors.affiliation: British Geological Survey Keyworth Nottingham UK.
authors.forename: R M
authors.initials: RM
authors.lastname: Lark
authors.affiliation: School of Agriculture Policy and Development University of Reading Earley Gate Reading UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Murdoch
authors.affiliation: Rothamsted Research Harpenden Hertfordshire UK.
authors.forename: J
authors.initials: J
authors.lastname: Storkey
keywords: Alopecurus myosuroides; black‐grass; geostatistics; nested sampling; reml; soil; weed patches