Root Length Growth of Eight Crop Species in Haplustoll Soils

Quantifying the dynamics of root growth is necessary for knowledge about development of rhizoplane and rhizosphere structure, and will indicate potentials for soil C sequestration and for water and nutrient usage. Root growth was measured during 3 yr in spring wheat ( Triticum aestivum L.) on fallow and in seven crops in spring wheat–winter wheat–alternative crop rotation under minimum tillage on Wilton silt loam (fine silty, mixed, superactive, frigid Pachic Haplustolls). Two types of minirhizotrons (standard [Stand MR] and pressurized‐wall [P‐wall MR]) were read with a microvideo camera. Average maximum rooting depths fell into agronomic groups: oilseeds safflower ( Carthamus tinctoris L.), 1.64 m, and sunflower ( Helianthus annuus L.), 1.45 m; spring wheat, 1.31 m; mustard family crops crambe ( Crambe abysinnica Hochst. ex R. E. Fr.), 1.17 m, and canola ( Brassica rapa ), 1.13 m; and legumes dry bean ( Phaseolus vulgaris L.), 1.00 m, soybean [ Glycine max (L.) Merr.], 0.99 m, and dry pea ( Pisum sativum L.), 0.99 m. Median depths of root length growth ranged from 0.92 m for safflower to 0.46 m for dry bean, and ratios of median to maximum depths averaged 0.51. Six out of eight crops showed greatest rooting depths in relatively wet 1995, likely because of wetter subsoil. Greatest total root length in safflower, crambe, canola, soybean and dry bean occurred in drier‐than‐average 1997, which is interpreted as a response to soil water deficit. Results indicate that diverse crop rotations have the potential to utilize water and nutrients and input C over different soil profile positions than spring wheat‐based monocropping.