Discovering the Effects of Drought on Soil: An afternoon with the Vacation Garden School
The Vacation Garden School is a summer camp for elementary school students that promotes stewardship of the earth and its resources. It is based at the Church of the Good Shepherd in Watertown, MA. The campers have visited Mount Auburn each of the past four summers and enjoyed activities relating to our diverse plant collections. This year the campers learned about soil prior to visiting Mount Auburn. On July 26, 2016 I planned to continue on this track by conducting an experiment with the campers demonstrating the water holding capacity of different soils. However, as eastern Massachusetts fell from moderate to severe drought, our time together evolved into a discussion on the effect of drought conditions on soil and the plant life it supports.
Originally, I planned to have the campers dig holes in several locations at Mount Auburn, each with a different soil composition. The campers would then fill each hole with water and let the water drain out. Once the water was gone, the campers would refill the holes with water and then measure the depth of the water with a yardstick. We would wait 15 minutes and re-measure the depth of the water. Once this was completed, the campers would multiply the difference from the first and second measurements by four to extrapolate the drainage rate of the soil per hour. The purpose of this experiment was to show the campers how a difference in soil composition affects the ability to store water and by extension, affects what plant material would be successful in that soil. For instance, a sandy soil drains quickly and therefore more drought resistant plants, such as sedums, are apt to be successful (with proper light conditions considered as well). Soils with higher amounts of organic matter have better structure and better water holding capacity. Most summer annuals, vegetables, and perennials are more successful in these conditions. Soils with higher organic matter also have greater diversity in the soil biology, resulting in much more activity in the rhizosphere, or root zone of the plant material. This zone is where the symbiotic relationship between soil organisms and plants sustains life.
The severe drought that we are experiencing is exhibiting obvious impacts on the landscape. Turf is brown and dormant. Leaves are wilting, and in some cases dropping. Mount Auburn is drawing from an aquifer (water below ground) at a higher than usual rate to sustain new plantings and some mature plants as well. Water has been pumped into Auburn and Halcyon lakes to support the aquatic wildlife in their battle for oxygen with algae blooms. The moisture content of the soil is non-existent and unable to meet the demands of all the competing root systems of the plant collection. Diversity of the soil biology has been depleted. The soil lacks the ability to prevent runoff and store rainwater.
In lieu of conducting the experiment as planned, the campers dug only one hole. We observed the lean, depleted look and structure of the soil. We looked at the all the plant material around us, noting the wilt of leaves and the brown turf areas and discussed the impact of drought on soil and plants, and the connection between the two. We also talked about the impacts of drought on our food supply and on wildlife, as well as the effects of erosion by wind and rain on the struggling soil.
In the end, we had a fine afternoon. The campers are concerned for the earth, and enthusiastic about science and experimentation. I hope that they will carry this curiosity with them throughout their lives.