1. A study of the effects of cultivation on root development of winter wheat was made in two Midlothian soils, Boghall and Corstrophene, during the years 1945–46 and 1946–47. Cultivation treatments consisted of ploughing to a depth of 8 in., deep cultivation (4 in.) and shallow cultivation (2 in.) with a tined cultivator.
2. Ploughing to a depth of 8 in. loosened the soil of the ploughed plots in the 4–8-in. layer and increased the non-capillary porosity of the soil (aeration) in this layer compared with the 4-in. and 2-in. tine cultivations. No significant differences existed between the treatments in respect of looseness of soil or its non-capillary porosity at depths of 0–4 in.
3. The effects of cultivation on root development were more pronounced at the later stage of growth in July than at the early stages. Compared with time cultivation, ploughing increased the number and lengths of roots at all depths in July, but only at the 10–20-cm. depth in the early stage of growth. No significant differences existed between the treatments in respect of average vertical root penetration at the early stages of growth. A deep root system with a large number of roots and with profuse branching developed after ploughing, and a shallow root system with a comparatively smaller number of roots and with sparse branching followed tine cultivation.
Increased non-capillary porosity of the soil at a depth of 10–20 cm. and the richer condition of the soil at this depth (formerly the upper layers, now inverted by ploughing) probably contributed to the greater root development in the ploughed plots at the early stage of growth, and presumably in July.
4. The degree of branching was affected by the depth of cultivation. Ploughing to a depth of 8 in. induced a higher degree of branching at 10–20-cm. and 20–30-cm. depths than did working the soil to 4 or 2 in. with a tine cultivator. Root branching of the second and third order occurred predominantly at depths below 10 cm., and that of the first order predominated at the 10-cm. level. The poorer conditions of soil moisture in the upper layers probably limited the degree of branching in these layers.
5. In the humid and rich soil of Boghall, a shallow root system of wheat developed, the majority of roots (74%) being in the 0–8-in. layer. Ploughing to 8 in. extended the spread of roots in the deeper layers of the soil in horizon A2 (8–12 in.), but restricted it in the upper layers of soil in horizon A1 (0–8 in.). It is doubtful if deepening the working depth of roots by ploughing in a rich soil offers any advantages over the 2–4-in. cultivations from the view point of water and nutrient supply.
6. At the early stages of plant growth top/root ratio in crop weight as well as in surface area was smaller with the 2-in. tine cultivation than with ploughing or 4-in. cultivation. No such differences existed between the treatments after manuring. A deficiency in the supply of nitrogen in the 2-in. tine-cultivated plots was indicated.