Choosing Planters for the School Cotton Patch

A Cotton Patch with Limits

A school garden club is planning a cotton patch in planting boxes. The boxes will stay in a bright, open part of the garden. Each box may contain at most 1,200 grams of dry soil. A volunteer can visit on Mondays to water by hand or refill a water tank. The club wants a design that helps cotton plants build new roots, stems, and leaves within these limits.

First, the club compares two soil amounts. Each box holds four cotton seedlings of similar starting size. Both receive the same light, normal outdoor air, temperature, and care. A cloth wick carries water from a tank to keep each box's roots moist. Water contains the same small supply of mineral nutrients. After six weeks, an adult harvests, cleans, and dries the plants and soil before weighing them. Drying removes stored water that could hide differences in newly built plant material.

Closely matched extra seedlings provide an estimated starting dry plant mass of 8 grams per box. The heavy-soil box starts with 2,400 grams of dry soil and ends with 2,398 grams. Its final dry plant mass is 44 grams. The light-soil box starts with 1,200 grams of dry soil and ends with 1,198 grams. Its final dry plant mass is 42 grams. Covers prevent soil spills, and the club collects fallen plant parts.

Next, the club tests three watering designs with new, matched groups of four seedlings. Each box starts with 1,200 grams of dry soil and an estimated 8 grams of dry plant mass. Soil type, mineral supply, light, air, temperature, and growing time stay the same. The club changes how water reaches the roots: a tank-fed wick, daily hand watering, or Monday hand watering. The graph shows the dry plant mass gained in six weeks.

The club also reads research notes. Leaves take in carbon dioxide, a gas in air. Researchers have traced material from this gas into new plant parts. They have also traced material from water into new plant parts. Roots take in water and small amounts of mineral nutrients. Light supplies energy for building plant parts; it does not supply building material. These findings help the club interpret its records.