Is the control of green area index of barley crops by application of alkaline materials possible in field conditions?

The risk of excessive leaf canopy growth in winter barley (Hordeum vulgare L.) grown in the UK is usually reduced by avoiding very early sowing at high seed rates, and in spring by delaying and reducing nitrogen fertilizer application. A preliminary study was conducted of a possible additional agronomic method for retarding winter barley leaf growth in spring. The study was based on previous plant physiological experiments showing that drought-induced reduction in leaf growth of barley is mediated by increasing alkalinity of the xylem sap. Leaf extension was measured in plants detached from the roots and fed artificial xylem sap adjusted to a wide range of pH. A field experiment tested the effects on barley canopy growth of solid calcium carbonate and alkaline pH buffer solution application to the foliage. Rate of leaf extension in the detached plant experiments decreased linearly with increasing artificial xylem sap pH, confirming the previous results in a different cultivar. Rate of canopy growth in the field experiment was halved by application of 1000 kg/ha of calcium carbonate up to four days after application. In contrast at six and eight days after application, following rain, compensatory growth occurred and the rate of increase in canopy size was larger with increasing calcium carbonate application rate. A pH buffer spray gave similar results but was less effective at reducing canopy growth. An improvement in persistence of the reduction in canopy growth by alkaline materials is needed before the potential for retarding leaf growth as an additional agronomic practice can be assessed.

► Aim was to study alkaline pH as a method for retarding leaf growth of barley.
► Leaf extension decreased with increasing artificial xylem sap pH in detached plants.
► Solid CaCO3 applied to foliage initially reduced, but later increased, canopy growth.
► Further research needed to improve persistence of reduction in canopy growth.