Plant density and yield of shoot dry material in maize in England

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Abstract
Yields of shoot dry material of maize at harvest in September or October are reported for 19 experiments involving differing plant densities within the range 3–36 pl/m2. The experiments were conducted at the Oxford University Field Station on a freely drained clay loam soil, adequately supplied with nutrients, in the years 1953–55, 1957–60, 1962–70.In one experiment, in the very dry season of 1964, yield/unit area recorded at a density of 14 pl/m2 was significantly higher than that obtained with a density of 31 pl/m3, but in all other experiments a satisfactory fit to the data was obtained with the asymptotic relationship between yield/unit area and density given by the equation w-1 = α+βρ, where w = weight per plant and ρ = density/unit area. The values of the parameters in this model give an indication of asymptotic yield (β-l) and of potential yield per plant when free from competitive stress (α-1). The estimated values of the parameters are given for the individual experiments, and comparisons are then made between the estimates obtained for contrasting varieties in seven experiments and for relatively early flowering European hybrids (Foliant & Inra 200) in ten different seasons.In direct comparisons between varieties, similar estimates of β were obtained for a very late variety (White Horsetooth) and much earlier flowering varieties of American (Wis. 275A) or European (Foliant) origin, but estimated values of α for White Horsetooth were lower than for Foliant and much lower than for Wis. 275A. Mean parameter values have been used to predict yield response to density in the differing varieties and the practical implications discussed.Estimated values of β in the model fitted to data for early European hybrids in differing seasons indicate that asymptotic yield of shoot dry material will be sharply lower in dry seasons, averaging 142 hkg/ha, than in seasons of more adequate rainfall, with an average of 187 hkg/ha. Values of a, however, were lower in the drier seasons, and it is suggested that this reflects the fact that drier seasons in Britain are normally warmer.Differences in spatial arrangement of plants were obtained by variations in row width, between 30 and 100 cm, or by changes in rectangularity – the ratio of the distances between rows and between plants in the row – from 1 to 9. Within these limits the pattern of yield response to density was not significantly affected, and at densities of 10–15 pl/m2 the average increment in yield associated with more even spacing was less than 5%.From the viewpoint of productivity, the predicted yield/density response curves show that a density of at least 10 pl/m2 is required for maize grown for fodder or silage in this country and, under irrigation or in areas where rainfall is less likely to be limiting, a density of 15 pl/m2 is preferable. Information on the effect of plant density on quality components in maize forage is surprisingly limited, but it is suggested that the fear of serious lodging at very high plant populations, rather than any possible decline in quality, is the main deterrent to further exploitation of environmental resources by increasing density.