Quadrat misuse: Confessions of a cover crop researcher's biomass sampling journey

Abstract

AbstractRectangular quadrats (1 m2 or less) are commonly used in cover crop research to sample shoot biomass in fields where the cover crops are planted in narrow rows. However, in drilled cover crops, quadrats do not accurately estimate cover crop biomass unless the width dimension of the quadrat, that runs perpendicular to the rows, is a multiple of the cover crop row spacing. Illustrations are provided with correctly sized and placed quadrats for sampling drilled cover crops along with calculations to convert sampled biomass to field‐scale units. Examples with various quadrat sizes, row spacings, and quadrat placements are used to illustrate how researchers can inadvertently underestimate or overestimate biomass by up to 49% and 27%, respectively. A survey of 92 articles with cover crop biomass data published in the Agronomy Journal and Weed Technology from 2017 to 2021 found that many studies used an incorrect quadrat size, which suggests that they may have inaccurately estimated cover crop biomass. However, assumptions were made to reach this conclusion because only a few papers provided the dimensions, orientation, and shape of the quadrat used. These results (1) raise important questions about possible errors made in papers reporting cover crop biomass data and associated metrics (nitrogen uptake, weed biomass, etc.), and (2) highlight the need for describing sampling methods in greater detail to ensure that accurate data and analysis are published in the literature. Approaches to correct possible errors in published research are described along with biomass sampling suggestions for future cover crop research.