Root Development and Subsoil 15N-labelled N Uptake in Soybean (Glycine max (L.) Merr.)

Abstract

The aim of this study was to investigate fertiliser-derived N uptake of soybean from different depths of the soil under field conditions. In addition, soybean root growth in sandy and loess soil was evaluated to understand the impact of site and soybean variety characteristics on soybean N uptake under continental conditions in Central Europe. Root analysis to determine rooting depth and root length density (RLD) was carried out using the profile wall method at three growth stages and two soybean cultivars (Glycine max (L.) Merr. cvs. Merlin and Sultana) in three consecutive years at two locations in eastern Germany. Fertiliser-derived N uptake of soybean from the soil surface and the subsoil was determined at 0.3 and 0.6 m depths using 15N-labelled nitrate N. Root studies showed that soybean roots grew up to 1.4 m on sandy and loess soil sites. Root length densities of up to 2.4 cm cm−3 were documented in the topsoil. By means of 15N application, soybean was shown to take up 15% of the surface-applied nitrogen in the dry growing season and 67 % in high rainfall years, between 19 and 77 % of the nitrogen placed at 0.3 m soil depth, and between 2 and 64 % of the nitrogen placed at 0.6 m soil depth by flowering. The field trials showed that soybeans can absorb a high proportion of the nitrogen placed in the subsoil by flowering time. Due to a well-developed root system reaching deep into the soil, soybeans are able to cover their N demand from soil-borne sources and secure yield formation during dry periods by water uptake from the subsoil.