ROOT-GROWTH AND WATER EXTRACTION PATTERNS FROM A CALCIC HORIZON

There is considerable uncertainty regarding the effectiveness of calcic horizons in supplying water to plants. We conducted a field experiment on Acuff fine sandy loam (fine-loamy, mixed, thermic Aridic Paleustoll) that contained a calcic horizon starting at 0.65- to 1.30-m depth. Sunflower (Helianthus annus L. 'Gro-Agri 380'), kochia (Kochia scoparia [L.] Schrader), and cotton (Gossypium hirsutum L. 'GSA-71') were grown to determine if (i) plant roots can proliferate readily within a calcic horizon, (ii) plant roots are as effective in extracting water from the calcic horizon as from overlying horizons and (iii) there are differences among the three species in the ability of their root systems to extract water from calcic horizons. We concluded that (i) plant roots proliferated readily in the calcic horizons, (ii) kochia roots were more effective in extracting water from the calcic horizon than from overlying layers, (iii) sunflower root systems were substantially more effective than cotton root systems in extracting water from calcic horizons, and (iv) plant roots seemed to be less effective in extracting water when they first entered a soil layer, compared with their effectiveness a few days later.