An assessment of the spaced-plant trial technique

Abstract

The study was designed to investigate the effects of ramet size, site conditions and fertilizer applications on the relative performance of plant populations, when grown in spaced-plant trials. The effects of other factors are also considered. Ten-fold differences in initial ramet size had little effect on the subsequent performance of eight contrasting genotypes of the grass species Anthoxanthum odoratum. Increasing the number of planted tillers per ramet from one to four slightly increased plant survival, but did not significantly affect plant height, plant yield or flowering date. Planting large tillers slightly increased plant yield but did not significantly affect plant survival, height or flowering date. The subsequent effects of initial ramet size were always small, compared with differences between genotypes, and there were no significant genotype × ramet size interactions. Six diverse populations of A. odoratum were grown in spaced-plant trials at three sites with contrasting soils, and with various additions of nitrogen and phosphorus fertilizer. There were large differences between populations in panicle height, vegetative height, shoot dry weight, flowering date and disease susceptibility. There were no significant population × N or population × P interactions, but there were significant population × site interactions for panicle height, shoot dry weight and mildew score, so that the performance of the various populations was not significantly correlated between sites. On the basis of this and other studies, we conclude that the relative performance of populations in spaced-plant trials is little affected by initial ramet size or by fertilizer applications. By contrast, relative performance is greatly affected by differences between sites in soil type and climate. The limitations of extrapolating the results of spaced-plant trials to the competitive conditions that normally exist in both natural and agricultural plant communities are briefly discussed.