Experimental methods with cotton: I. The design of plots for variety trials

Abstract

1. The results of three uniformity trials with a U4 cotton at Barberton are reported. Two of these trials, carried out in a dry year, gave yields in the region of 400 lb. seed cotton per acre; the third, in a wet year, yielded over 1100 lb. per acre.2. Results from the three experiments agreed closely in essential details regarding size and shape of plots.3. In all three cases the percentage standard error per plot decreased rapidly as the plot was lengthened, but tended to increase slightly as the width of the plot was increased.4. The standard error increased as the block size was increased by the addition of more plots, indicating the desirability of keeping the number of strains in a variety trial as low as possible.5. With plots of the same shape the smallest plots were the most efficient, while with plots of the same size the efficiency increased as the plot shape became longer and narrower.6. Two fertility contour maps are given, which illustrate a general patchiness in yield common to cotton crops in the Barberton district.7. Details of the types of plot used at Barberton are given, together with the reasons for their adoption.