Avoiding edge effects in agroforestry experiments; the use of neighbour-balanced designs and guard areas

Abstract

A number of different types of edge effects on experimental plots are defined, and it is shown that they are frequently important in agroforestry experiments. Methods of eliminating edge effects, either at the design or the analysis stage, are described. Computer simulations, based on uniformity data, are used to investigate the efficacy of neighbourbalanced designs, with and without neighbour terms, for reducing the problem of neighbour effects between different treatments. It is concluded that, while neighbour-balanced designs may be useful in certain situations or in combination with other methods, it is preferable to eliminate edge effects by using adequate guard rows. Recommendations are therefore made concerning the correct use of guard areas in agroforestry experimentation.

Development and assessment of a network of water meters and rain gauges for determining the water balance. New SCADA monitoring software

“…2 illustrates, the pots were arranged in two irrigation zones each consisting of two rows of eight pots. Pots under study are outlined in white while those used to eliminate border effects (Allen et al, 1998;Davis et al, 2012;Langton, 1990) are outlined in red. These pots were irrigated independently from those under study.…”

Experiment designs to evaluate inter- and intra-specific interactions in mixed plantings of forest trees

“…It is desirable and customary to use guard (or buffer) rows to reduce edge-effects in experiments (Langton, 1991). In the Atherton trial, the outermost row in each plot was designated a guard row, providing two guard rows between treatments.…”

Circular neighbour-balanced designs and one-sided circular neighbour-balanced designs

“…The design where the plots are in 2-dimensions i.e. the design in which a treatment on a plot influences the responses of the two neighbour plots, is studied and also many contributions have been made in the literatures of Azais et al (1993), Smart et al (1994), Langton (1990) and David and Kempton (1996). Bailey (2003) has developed such designs concerned with the study of one sided neighbour effects.…”