Methods of adjustment for two-dimensional spatial heterogeneity of gra
in yield were investigated for 224 UK cereal trials. The methods used
row and column 'block' analysis of plot yields and neighbour analysis
based on first differences of plot yields. In 36 % of trial analyses f
or block models and 30 % for neighbour models the average variance of
variety differences was reduced by more than 10 % compared with the be
tter of the one-dimensional row or column models. Compared with comple
te blocks, 2-D block analysis had a mean efficiency of 153 % whereas t
he conventional 1-D block analysis (by rows) had a mean efficiency of
127 %. Similarly, 2-D neighbour analysis had a mean efficiency of 159
% whereas the 1-D analysis had a mean efficiency of 137 %. Recently, g
eneral statistical methods have been developed for two-dimensional des
ign and analysis; their wider use should lead to major gains in the pr
ecision of variety trials.