Nitrogen supply to cereals and sugar beet by mass flow and diffusion on a silty loam soil

Abstract

Abstract In a four‐year field study the nitrogen supply by mass flow and diffusion to cereals (spring wheat, winter barley, winter wheat) and sugar beet was investigated on a silty loam soil. The rates of water withdrawal, N mass flow and N diffusion were determined as a function of soil depth and time. The contribution to the N supply to roots by mass flow was 15–33% and mainly confined to the topsoil layer. The N supply by diffusion plays with 67–85% the dominant role, particularly in deeper rootzone layers. During periods of high N uptake, the N inflow (per unit root length and time) ranges between 0.26–2.07 μmol/(m · d) at various rootzone layers for cereal, and between 3.80–8.98 μmol/(m · d) for sugar beet, respectively. As a consequence of the high proportion of diffusion supply, at harvest the whole rootzone was largely depleted of nitrate. Thus, nitrate leaching losses during winter were small, the average nitrate concentration of the yearly groundwater recharge being only 7.9 mg N/l. Additionally, some results on supply of K, Ca, Mg and Cl for spring wheat and sugar beet are given. Diffusion supply prevails for K, and in the case of sugar beet for Mg and Cl also. Mass flow of Ca exceeded uptake considerably.