Soil structure has a greater effect on the rooting of wheat (Triticum aestivum L.) than nitrogen fertilisation rate or genotype.

Despite extensive research over the last century concerning the application of nitrogen fertilizer to support the production of wheat (Triticum aestivum L.), our understanding on how this impacts on root growth in subsoils is limited. In this study, we investigated how different rates of nitrogen fertilization (100, 200 and 350 kg/ha N) affected the root and shoot growth of three different wheat genotypes. We collected field soil cores to a depth of 100 cm and scanned them using X-ray Computed Tomography (CT) to quantify the volume of macropores and stony material. The collected soil cores were then destructively segmented to determine root number density. Our results showed nitrogen fertilization rate had a limited effect on root growth and proliferation in both the topsoil and subsoil. Furthermore, wheat genotype did not play a significant role in determining root growth at any depth, with no significant differences between the different genotypes. However, soil macroporosity was positively correlated to root number density, accounting for 48% of the variation. Our results provide evidence that soil management (e.g. cultivation techniques) may be the key to improving subsoil rooting regardless of crop genotype and nitrogen rates applied.