Utilization of mineral nitrogen in the subsoil by winter wheat

Abstract Uptake of nitrogen from the subsoil (30–200 cm) by winter wheat has been measured in field experiments on deep loess‐parabrown soils in northern Germany and at Rothamsted (England) for different crop rotations and manuring schemes. The results can be summarised as follows: The mineral nitrogen content of the subsoil varies widely depending on farming practice. The effective depth limit for N uptake by winter wheat appears to be 150 cm. Averaged over 22 sites, 33% of the total N uptake was from the subsoil (range 9–75%); 25% was from the 30–90 cm soil layer and 8% from the 90–150 cm soil layer. Decreasing the N supply to the topsoil increased N uptake from the subsoil. N uptake from the subsoil is not dependent on water uptake from the subsoil; nitrate is readily transported to absorbing roots by diffusion. When deciding on the rate of fertilizer N to apply in early spring, soil mineral N to a depth of 90 cm should be taken into account. For subsequent dressings, the soil mineral N between 90–150 cm depth needs to be considered.