Doctoral Dissertations

Date of Award

8-1983

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

David L. Coffey

Abstract

The use of fresh spent mushroom compost (SMC) and SMC which had been aerobically composted for five weeks as replacements for peat in soilless media were studied.

Determination of physical and chemical characteristics revealed that fresh and aged SMC had high concentrations of calcium and potassium, high percentages of air space, low water buffering capacities, and high soluble salt concentrations. Fresh SMC had very high levels of ammonium, was basic, shrank excessively, and held little easily available water. Aged SMC held adequate amounts of easily available water, contained low levels of ammonium, and had a pH near neutral.

Lettuce (Lactuca sativa L.), tomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativus L.), and marigold (Tagetes patula L.) transplants were grown from seed in leached and unleached potting mixes containing 0, 25, or 50% (by volume) peat and/or fresh or aged SMC, with 50% vermiculite. Heights, quality ratings, dry weights, percent dry weights, and tissue element concentrations were measured. Plants similar to control plants were produced in 25% aged SMC, with 25% peat and 50% vermiculite. Acceptable plants of slightly reduced quality were produced in 50% aged SMC with 50% vermiculite. Reduced growth and symptoms of ammonium toxicity were seen in plants grown in fresh SMC. Leaching improved yields of lettuce and marigolds grown in 25% SMC and of all crops grown in 50% SMC. Tissue concentrations of calcium and potassium were higher and of magnesium and phosphorus were lower in plants grown in SMC than in those in the control mix.

Broccoli (Brassica oleracea L. var. italica), lettuce, tomato, and marigold transplants were grown from seed in media containing 50% vermiculite (by volume), fresh or aged SMC in a range of levels from 0 to 50%, and peat (comprising the remaining portion). Heights, dry weights, and percent dry weights were measured. Crop responses to fresh and aged SMC had significant linear and quadratic trends. Generally, percent dry weight decreased linearly, while dry weight and height rose initially and then dropped as the level of SMC in the growing medium increased. Lettuce, marigolds, and tomatoes grew best in 25% aged SMC, while cucumbers grew best in 37.5% aged SMC.

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