Variable responses of maize roots at the seedling stage to artificial biopores in noncompacted and compacted soil

Purpose The objective of this study was to test the hypothesis that the presence of biopores in compacted soil affects the behavior and promotes the growth of maize roots and their uptake of N from fertilizer applied to subsoil. Materials and methods Disturbed Vertisols with a clay loam soil texture were collected for a column experiment. Artificial biopores (2 mm diameter) were created in noncompacted (1.3 g cm(-3)) and compacted (1.6 g cm(-3)) soil columns. The root architectures of maize and their interactions with biopores were quantified in three dimensions with X-ray computed tomography and image analysis. The N uptake from the lower part of the soil column (100-150 mm) was measured with (15) N-labeled urea (Nlab-low). Results The number of biopores colonized by roots in the compacted soil was 2.7 times higher than that in the noncompacted soil, while in the noncompacted soil, the number of biopores crossed by roots was significantly larger than that in the compacted soil (P < 0.05). The presence of biopores with 2 mm diameter in the compacted did not improve maize growth at the seedling stage, likely due to poor contact between the roots and the biopore walls. A significant linear relationship between root surface area in the lower part of the column and shoot Nlab-low uptake (r = 0.72, P = 0.002) was observed. However, this relationship was not changed (r = 0.72, P = 0.002) when the surface area of roots that intersected biopores was removed from the model, indicating a negligible role of the roots growing within biopores in absorbing Nlab-low. Conclusions The behaviors of roots encountering biopores included colonization in the compacted soil but only crossing in the noncompacted soil. In the compacted soil, the biopores, which were 2 mm in diameter, had minor impacts on crop growth and nutrient uptake at the seedling stage, in which direct contact between the root and biopore wall played a critical role.

Automated summary

This study investigated the effects of biopores on the behavior and nitrogen uptake of maize roots in compacted soil. The results showed that the number of biopores colonized by roots was higher in compacted soil compared to noncompacted soil. However, the presence of 2 mm diameter biopores did not significantly improve maize growth and nitrogen uptake at the seedling stage.