Sowing Depth and Soil Water Effects on Seedling Emergence and Root Morphology of Three Warm‐Season Grasses

Abstract

AbstractGreater seed burial has been suggested as a way to increase the time of water availability to seeds and seedlings in revegetation of semiarid rangelands. The effects of sowing depth on seedling emergence and root development of ‘Vaughn’ side‐oats grama [Bouteloua curtipendula (Michx.) Torr.], ‘A‐130‘ blue panic (Panicum antidotale Retz.), and ‘Cochise’ atherstone Iovegrass (Eragrostis lehmanniana Nees × E. tricophora Coss. & Dur.) were measured in relation to water availability on a sandy loam soil in the greenhouse. Side‐oats grama and blue panic were sown at depths of 0, 10, 20, and 30 mm, while Cochise lovegrass was sown 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 greenhouse were initially higher and decreased more rapidly than those of field seedbeds. Seedling emergence was generally highest from surface‐sown 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. Adventitious 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 enough 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. Frequent rainfall is apparently necessary to permit adventitious root development and establishment of these species.