The effects of drying of the topsoil and of micronutrients in the subsoil on micronutrient uptake by an intermittently defoliated ryegrass

Summary A glasshouse experiment was conducted to study the effects of water content of the topsoil on the micronutrient nutrition of Italian ryegrass (Lolium multiflorum Lam.) growing in a siliceous sandy soil of marginal micronutrient status, with and without a supply of micronutrients at lower depths. The main objectives were to investigate whether micronutrient supplies would be sustained for the regrowth of defoliated grass after the topsoil had dried, and to assess the contribution made by small amounts of micronutrients in the subsoil to nutrient supply.In the absence of supply from deeper layers, topsoil drying rapidly induced deficiency of micronutrients, particularly of manganese, resulting in significant yield depression. When small amounts of micronutrients were present in a deeper, wet layer there was little reduction in yield after the topsoil had dried.The evidence suggests that, provided the roots had access to water in the subsoils, significant amounts of manganese, zinc and copper can be absorbed from topsoils as dry or drier than wilting point. Supply of micronutrients to the subsoil appears to have enhanced the efficiency of manganese absorption from dry topsoil.