The Influence of Environment on Seed and Seedling Mortality: III. The Influence of Aspect on Maize Germination

Abstract

Ecologists and agronomists have long been interested in the influence of aspect on the development of both natural vegetation and crops. The previous investigations have been along three main lines: (a) phytogeographical investigations, e.g. the early studies of alpine vegetation on different mountain aspects by De Candolle (1855) and Sendtner (1854), (b) correlations between insolation and plant distribution, e.g. Boyko 1945, 1947a and b, (c) direct measurement of soil temperature on natural and artificial slopes, e.g. Ashbel (1942) and work reviewed by Geiger (1950). Agronomists have observed differences between the growth of crops on different aspects and slopes but no detailed observations or experiments are known to the authors. Most of the observations are general such as the work of Prosser-Jones (1951) who noted that in the Dale area of Pembrokeshire, early potatoes were planted on fields of southern aspect. On the other hand, Kentish fruit farmers avoid southern slopes for orchards, lest the increased warmth of such areas in early spring lead to earlier flowering and increased liability to frost damage (private communication). One of the problems encountered in the extension of maize cultivation into more northern temperate regions is the combination of low temperatures and high water content of the seed bed which results in the rotting of the grain (see Harper et al., 1955b; Harper, 1955 and Wernham, 1951). Thus in Holland, where acreage has expanded rapidly since 1947 maize has proved to be a crop for the warm sandy soils of the south-eastern provinces. In England it seemed that a careful choice of site would be necessary to ensure as far as possible quick and even emergence, and it was decided that a critical analysis of the influence of aspect would merit consideration. In the earlier papers of this series (Harper, Landragin and Ludwig, 1955a, b) it was shown that the rate and extent of emergence of maize in the field is largely determined by soil temperature and moisture. In this investigation the soil temperature was varied in the field by building mounds of different slopes so that the direct influences of aspect and slope on the temperature of these could be assessed, together with the effects on the rate and extent of emergence of maize. In addition, the inquiry was widened to include varietal and sowing-date factors in the multifactorial experiments.