No abstract

Greater 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.

Location of seeds in the scedbed may affect germination and seedling establishment of range grasses. Our objective was to determine the effects of trampling by livestock and mechanical secdbed preparation on burial of grass seed on a sandy loam seedbed. Plots were root plowed or ripped then broadeast seeded, or broadcast seeded then iigbtly or heavily trampled by cattle or land imprinted before summer rains. Seedbeds were sampled by extracting soil plugs with plastic vials, splitting the plugs, and determining seed location with a dissecting scope. Sampling occurred after treatment, after summer thunderstorms, and after seedling emergence. An average of 75, 42, 17, and 7% of seeds found were buried immediately after heavy trampling, land imprinting, light trampling, and no disturbance, respectively. After summer thunderstorms an average of 78,72,63,40, and 29% of seeds found were buried on plots root plowed or ripped, heavily trampled, imprinted, lightly trampled, and undisturbed, respectively. Although bigb percentages of seeds were buried on plots heavily trampled, imprinted, and root plowed or ripped, many of these seeds were too deep for seedling emergence. Smaller-seeded blue panic (Pa&urn antidotale) and the lovegrasses (Eragrostis lehmandana Nees and Eragrostis lehmandana Nees XE. trlcbopbera) were buried by treatment and rain better than sideoats grama [Bouleloua curtipu#da (Micbx) Tot?.].

Successful germination and establishment of grass seedlings from surface-sown seeds requires a microsite which provides nde quate soil water and temperature conditions, among other speciesspecific requirements. The microsite where these requirements are met has been termed a "safesite". Safesites may occur naturally as cracks and depressions in the soil surface, gravel, and plant litter, or be prepared by seedbed equipment and livestock trampling. A greenhouse study was conducted to determine the intluence of seedbed microsite characteristics and soil water treatments on seedling emergence of 'Vaughn' sideoats gramn (Bouteloua curtipendula (Michx.) Torr.), 'A-130' blue panic (Panicurn antidotule Retz.), and 'Cochise' Atherstone lovegrass (Eragrostis lehmanniana Nees X E. tricophera Coss and Dur.). Although there were several interactions, in general, emergence of all 3 species was highest from gravel, followed by litter, cracks, and finally the bare soil surface. Bare surface sites decreased in water content more quickly than the other sites. Cochise lovegrass had high emergence in gravel under all water treatments. Small-seeded species such as Cochise lovegrass broadcast on coarse-textured surface soils may establish with minimal seedbed preparation, provided summer precipitation is adequate.

No abstract