The root activity of cereals and peas when grown in pure stands and mixtures

Lithium was used as a non-radioactive tracer to investigate the root activity of two cereals (wheat and barley), and of two contrasting cultivars of pea (leafy and semi-leafless), both in pure stands and in mixtures. The mixtures included combinations of each cereal with each pea cultivar in single rows, alternative rows and cross-drilled. Total lithium uptake (mg m^-2) was higher for wheat than for barley, and higher for semi-leafless pea than for leafy peas. Growing cereals with peas reduced the total lithium uptake by peas, compared with pure stands, especially in alternate-row mixtures. Growing peas with cereals only reduced the total Li uptake by cereals when they were cross-drilled. The Li uptake by wheat, barley and peas generally decreased with soil depth in a similar manner; however, semi-leafless peas absorbed proportionately more Li from close to the soil surface than did leafy peas. Both pea cultivars absorbed more Li at 10–20 cm depth when grown in intimate mixtures with cereals, compared with less intimate mixtures or pure stands. The potential of lithium as a non-radioactive tracer in mixed-cropping studies is briefly discussed.