SOWING DEPTH AND SOIL-WATER EFFECTS ON SEEDLING EMERGENCE AND ROOT MORPHOLOGY OF 3 WARM-SEASON GRASSES

Greater seed burial has been suggested as a way to increase the time o f water availability to seeds and seedlings in revegetation of semiari d rangelands. The effects of sowing depth on seedling emergence and ro ot development of 'Vaughn' side-oats grama [Bouteloua curtipendula (Mi chx.) Torr.], 'A-130' blue panic (Panicum antidotale Retz.), and 'Coch ise' atherstone lovegrass (Eragrostis lehmanniana Nees x E. tricophora Coss. & Dur.) were measured in relation to water availability on a sa ndy loam soil in the greenhouse. Side-oats grama and blue panic were s own at depths of 0, 10, 20, and 30 mm, while Cochise lovegrass was sow n at 0, 5, 10, and 15 mm. Pots were subirrigated every 3 d, on Days 1 and 7 after sowing, or on Day 1 only. Soil water contents in the green house were initially higher and decreased more rapidly than those of f ield seedbeds. Seedling emergence was generally highest from surface-s own seeds and decreased with depth of sowing, possibly due to lack of aeration. All three warm-season grasses elongated their subcoleoptile internodes to place the coleoptilar node and site of adventitious root initiation near the soil surface, regardless of sowing depth. Adventi tious roots required 9 to 13 d of available water to initiate. Seminal root growth and depth were not increased with increased sowing depth. Seminal root elongation rates from 5.8 to 8.7 mm d-1 are not fast eno ugh to stay ahead of a typical drying front of 15 to 20 mm d-1 during the summer rainy season on sandy loam soils in southern Arizona. Frequ ent rainfall is apparently necessary to permit adventitious root devel opment and establishment of these species.