Effects of biopores on the growth and N-uptake of wheat at three levels of soil moisture

Abstract

Roots grow more rapidly through soil spaces such as vacated root channels than through undisturbed soil. This experiment was conducted to determine the extent to which transfer of nutrients is compromised by gaps between the pore wall and the root. Undisturbed cores were obtained from a no-till Dark Brown Chernozemic soil. The cores were divided into three 2.5-cm-thick segments (3.8–6.3 cm, 7.8–10.3 cm, and 11.75–14.25 cm soil layers). The density of 200–500 μm (P200) and 500–1000 μm (P500) diameter pores was visually assessed in each segment. The cores were adjusted to water potentials of − 0.01, − 0.1 and − 1.5 MPa by adding K15NO3-labelled water. Pots containing wheat (Triticum aestivum) plants were placed on top of the cores and the number of roots that appeared at the bottom of the cores, the root length within the cores, and shoot 15N content were measured after 72 h. Small pore (P200) density had no effect on root number at any moisture level. Large pore (P500) density correlated positively with root number at − 0.10 MPa (r2 = 0.57) and − 1.5 Mpa (r2 = 0.68). The equation relating shoot 15N content and root number had a common slope across all moisture treatments, suggesting that the rates of N-uptake per unit root were not compromised by macropore-assisted root growth at the investigated moisture levels. It is unclear if uptake is directly across the pore or via laterals growing outside the pore wall. N-uptake per unit root length of roots growing through soil pores may be compromised at moderate levels of soil moisture. Key words: Biopores, macroporosity, N-uptake, nitrogen, penetrometer resistance, root growth