S. D. Merrill, D. L. Tanaka, J. M. Krupinsky, and R. E. Ries
Abstract
Root growth of safflower was studied with a minirhizotron-microvideo system in field studies conducted on Typic and Pachic Haploborolls. The system consists of clear plastic tubes, 2- or 3-m long, installed in the field and read with a miniature video camera that magnifies images. Root growth was measured for two years in Study 1 with three seeding date treatments. The average median depth (half of total root length above, half below) observed at root growth maximum was 1.02 m, and average maximum depth was 1.65 m. In Study 2, median and maximum root growth depths of safflower were found to be greater than those of seven other crops: dry bean (Phaseolus vulgarus L.); dry pea (Pisum sativum L.); soybean (Glycine max (L.) Merr.), canola (Brassica rapa), crambe (Crambe abysinnica), spring wheat (Triticum aestivum L.), and sunflower (Helianthus anuus L.). Average median depths at dates of greatest root growth for 1995, 1996, and 1997 were 1.09, 0.75, and 0.90 m, respectively; greatest maximum depths were 1.77, 1.52, and 1.64 m, respectively. Soil water depletion measured by a neutron moisture meter was added to seasonal precipitation to quantify water use. Of the seven crops observed in Study 2, only sunflower had greater water use than safflower during the three years. Measurements of water use by 10 crops in Study 3 confirmed that sunflower was the greatest water user and that safflower was the second greatest, and both crops were shown to withdraw from 3 cm to greater than 10 cm more water than did other crops. Safflower, with its taproot-organized root growth system, is the most deeply rooted of the crops commonly grown in the Northern Great Plains, and has the capability of extracting subsoil water at greater depths than all other crops studied.
Key words: root growth, water use