Most of the soil investigations in this country have been conducted at Rothamsted or other parts of South Britain and the soils examined have been chiefly those overlying the stratified rocks of the southern half of England. These, however, are by no means typical of the whole of Britain and research is needed into soils found extensively in Scotland and other parts of Britain which differ greatly in their origin, nature and properties from those which have hitherto been the chief subjects to which British investigators have devoted attention. The various agricultural colleges are taking up the study of the soils of their respective districts, and when the Farm of Craibstone was acquired as an Experiment Station by the North of Scotland College, a series of soil investigations was immediately commenced.

Accounts have already been published by this department of investigations made as to the origin, nature and properties of the glacial drift soils of the north-east of Scotland; in particular, the soil as found at the Experimental Farm of Craibstone, near Aberdeen, has been studied by means of mechanical analysis and the determination of the chemical composition of the fractions resulting therefrom (4). The results obtained have brought out some characteristic features of the Craibstone soil, and have indicated that important differences may exist between a glacial drift soil, derived mainly from rocks of granitic nature, and such a soil as that of Rothamsted, arising from the “Clay with flints” formation.

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Infiltration into the soil is regulated in part by sealing of the soil surface by raindrop impact. Soil surfaces protected from such impact maintained higher rates of infiltration than exposed soil surfaces. It was hypothesized that the cover particles protected the covered portion of the soil and prevented the reaction of raindrop impact on the sot1 state. The soil under the cover particles remained in the original state in which infiltration could occur. However, since the cover particles in this study were impervious, infiltration could not occur on the covered area but would occur along the available perimeter of the cover particles. Water would then move in both vertical and lateral directions. The effective lateral distance that the water moved after entry was defined as the effective width. To evaluate the effects of soil surface cover on the infiltration rate of soils exposed to raindrop impact, simulated rainfall was applied at a constant rate to one soil type in small plots with free drainage, and square and rectangular cover particles of varying sizes and percentages were used as surface cover. THEORY AND PROCEDURE Infiltration involves three interacting phases:(1) the surface entry of water, (2) the available storage capacity of the soil, and (3) the movement of water through the soil profile. The surface entry of water controls the rate of infiltration during all periods when water can be stored in the soil or passed downward through the soil profile more rapidly than it can penetrate the soil. Generally the initial infiltration rate is high. The rate diminishes, however, during continued rainfall toward a nearly constant lower rate.The initial rate, the rate of decrease, and the final rate are affected by characteristics and conditions of the soil surface, soil profile, and rainfall.