The Best Plant Food (page 2)

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Author: Janice VanCleave


Your results may vary, but the author found that at the end of four weeks the nutrient-fed plants had stronger stems and greener leaves.


Many nutrients needed for plant growth are soluble (able to break up and thoroughly mix with another substance) in water. Thus, when mixed with water they form an aqueous solution, which is a mixture in which one or more substances are dissolved in water. (Dissolve means to break into very small particles and mix thoroughly with a liquid.) Nutrients in soil can be removed by a process called leaching. Leaching is the removal of soluble chemicals from a material, such as soil, by filtering water through the material so that water-soluble substances are extracted. In this experiment, the cheesecloth acts as a filter (material that allows a liquid, but not solids, to pass through) and the liquid passing through the cheesecloth is called the filtrate (liquid that passes through a filter). The filtrate collected by leaching is rich in nutrients. Plants grown with this nutrient liquid grow better than plants grown in the washed soil without nutrients. Plants without soil nutrients continue to make food in their leaves by photosynthesis, but photosynthesis alone is not enough to sustain the plants. The nutrients taken in by the roots are necessary for proper growth and maintenance of plant cells. Lack of nutrients results in many problems, including yellow leaves, wilting, thin foliage, small leaves, and generally poor growth.

Try New Approaches

Do all soils contain the same nutrients? Repeat the experiment using samples of soils taken from different locations. Remove any ground covering, grass, and/or plants growing in the soil. Be sure to label the soil samples and make notes of the types of plants growing in the soil and in the general area from which each sample is taken (see Figure 26.2). This information can be used later to determine the nutrients needed by these plants. Use leached water from the different soil samples to grow plants. Determine which nutrient filtrate is the best for the plants used.

Nutrient Differences in Soils

Design Your Own Experiment

The types of nutrients in soil can be determined with an inexpensive soil-testing kit. (Your teacher can order this from a plant nursery or a science supply company. See Appendix 9 for a list.) Design an experiment to compare the effect of specific nutrients, such as nitrates and phosphates, on plants. One way is to repeat the original experiment, but test for and identify the presence of some of the nutrients. Record your testing results in a Nutrient Soil Data table like Table 26.1. You may wish to include information in the table about where the soil was found, as shown in Table 26.1.

Get the Facts

Plants look unhealthy when they do not have proper nutrients. Use a gardening book to determine the nutrients needed for proper plant growth for the plants in your experiments and the symptoms that indicate a deficiency of each nutrient.

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