The Distribution of Wheat and Maize Roots as Influenced by Biopores in a Subsoil of the Kanto Loam Type

Abstract Biopores are tubular soil macropores left by plant roots after their decay or burrowed by soil animals, which provide channels for deep rooting and improve crop access to water and nutrients. The density oi biopores, number of biopores per unit area, and proportion of biopores occupied by roots were measured on horizontal soil profiles at 30, 50, and 70 cm in depth in a fine-texture subsoil of Andosol (Light clay, a volcanic ash of the Kanto loam type) at the mature stage of wheat and maize. Images of 0,1 mm resolution from the pictures of cleaned profile surfaces were examined on a computer display. Dark spots with a circular and smooth boundary were regarded as biopores. The density of biopores larger than 1 mm in diameter ranged from 500 to 2,000 m–2. The percentage of biopores occupied by roots was more than 30% of biopores larger than 1 mm and increased with depth. Roots were accumulated in biopores. The proportion of biopores (> 1 mm) with roots increased with depth. It was 28-35% in the wheat plot and 14-20% in the maize plot. This suggested that thinner wheat roots easily entered a biopore and remained in it. The possible influence of biopores on the spatial distribution of roots was discussed.