ANALYSES OF YIELD FROM A COMPETITION TRIAL WITH PERENNIAL RYEGRASS

Four varieties of perennial ryegrass, (S24, S321, S23 and Endura), were grown in monoculture and in all possible binary mixtures. Three spatial arrangements of varieties within mixtures were used. Total DM yields were recorded from nine harvests during 1969 for mooocultures and mixtures and for the mixture components. The arrangement of varieties within mixtures had no effect on the total DM yield of the mixtures. Monocultures and mixtures did not differ significantly in yield at any harvest or in annual total, bnt there were differences between monocultures at some harvests. No differences between mixtures were detected. The experiment took the form of a competition diallel in which monocultures corresponded to the parents in a genetic diallel and mixtures to the crosses between these parents. There was a significant interaction hetween the rows (i.e. main variety effects) and the columns (i.e. associated variety effects) of the diallel table only at the first harvest. The change in the competitive ability of the four varieties throughout the season was examined. The relative ranking order of varieties for competitive ability altered as the season progressed.     

THE EFFECT OF NITROGENOUS FERTILIZER ON THE RATE OF GROWTH OF ITALIAN RYEGRASS.

Residual response to an initial application of nitrogen was measured in 3 years and was found to be quite large, e.g. a response of 8 Ib DM per extra Ib N at the first harvest, when applying 125 Ib N/ac (140 kg/ha) rather than‘75 Ib (84 kg/ha) and allowing 6 weeks' growth, was increased to 21 Ib DM when yield from residual cuts was taken into account. Response was large in relation to the amount of N estimated to have been left behind after the first harvest. Marginal recovery of N, already quite high at the first harvest, was increased to a little over 90% when yield from residual cuts was taken into account Recovery, however, was lower than this when 10 weeks' growth was allowed before the first harvest, and it seems that, in this case, some N may have been lost from the system. A supplementary experiment suggested that the residual effect of N on DM yield could be obscured to some extent by fresh applications of N.     

The measurement and interpretation of genotype-environment interactions

Summary The regression analysis developed by Finlay and Wilkinson to investigate genotype-environment interactions and to assess genotypes for their adaptation to a range of environments is reviewed. Their analysis used the mean yield of many genotypes to provide a measure of the environment; it was not measured in physical terms. To reveal aspects of their analysis it was applied to data of the response of genotypes to variation in a single precisely measured environmental factor. The conclusions were extended to consider variation in several environmental factors.The effects on the regression statistics that occur with different samples of genotypes, sub- and super-optimal environmental conditions, differences in periods of growth, changes in the scale of measurement and the occurrence of several stress factors are outlined.The study byBreese (1969) of genotype-environment interaction inDactylis glomerata is considered against a background of these effects.