Date of Award

Winter 1986

Project Type

Dissertation

Program or Major

Plant Science

Degree Name

Doctor of Philosophy

Abstract

Field and greenhouse studies were conducted to examine the seedling vigor of sod-sown alfalfa (Medicago sativa L.).

Seedlings grown in tilled soil had more dry matter, were taller, and had longer internodes than seedlings in sod. Node number and plant density were reduced in some experiments. Seedling vigor was not hindered by physical impairment of seed germination, inadequate soil fertility, weed or sod competition, soil moisture, herbicide injury, or predators.

Time interval between tillage of sod and planting date affected seedling vigor. Seedlings growing in sod tilled the previous fall had higher yields than those sown in freshly tilled sod or in sod itself. At a second seeding, six weeks later, seedlings sown in sod tilled that spring were comparable to those in sod tilled the previous fall, while sod-sown seedlings continued to be inhibited. Seedlings sown in August following tillage 115 days before seeding had higher yields than those sown in sod or in sod tilled 62 days before seeding.

A water soluble toxin was found in ground dry sod collected from the field. Solutions of two salts (KCl or NaCl) with comparable electrical conductivities did not inhibit alfalfa seedlings germinating in petri dishes. Under greenhouse conditions, ground sod incorporated into field soil at 5 or 10% (w/w) inhibited alfalfa seedling yield and reduced leaf area, compared to those sown in unamended field soil. Increased watering level accentuated this effect, indicating that anaerobic conditions may favor inhibition.

Cores of sod evolved 8-10 times more ethylene over 12 days, compared with tilled soil. Alfalfa seedlings exposed to 6.6 mPa ethylene continuously for 14 days were shorter, had smaller yields, and had less leaf area than those exposed to air. The appearance was vey similar to damage incurred by sod-sown seedlings in the field or greenhouse.

Ethylene may be one of many potential toxins in decaying sod which inhibits alfalfa seedlings. Other toxins may be released and/or produced by the decaying sod. They appear to be present in killed sod, dissipate over time, and their disappearance is accelerated by tillage.

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