Passage IV

Compost consists largely of organic matter that has been decomposed by bacteria that require oxygen. Compost is used as soil fertilizer. Two studies were done to examine the effect of compost use on the growth and yield of bean plants.

Study 1

Four different materials were selected for composting—coffee grounds, pine needles, crushed eggshells, and alfalfa (a plant). Each material was placed in a separate container. A small amount of distilled water was added to each material. The 4 containers were then left in a warm location for about a week to allow the materials to decompose. During the week, the materials were stirred periodically and moistened with distilled water. The decomposition process was considered complete when the temperature at the center of the material had risen to 40°C. For each type of compost, the pH, and the nitrogen, phosphorus, and potassium contents were then determined (see Table 1).

Study 2

Each type of compost was added to 2 different amounts of a given soil to create mixtures that were either 20% compost or 50% compost. A ninth mixture contained 10% pine needles, 50% crushed eggshells, 20% alfalfa, and 20% soil. Each mixture was used to fill 5 pots. Ten bean seeds were planted in each pot. All pots received the same amount of light and distilled water. After 6 weeks, the number of mature bean plants growing in the pots and the number of bean pods on each plant were counted for each mixture. The percent of seeds that produced mature bean plants for each mixture is shown in Table 2. Figure 1 shows, for those plants that produced bean pods, the average number of bean pods present on mature bean plants growing in each mixture.