March 13, 2012

FOOD & AG: The Forgotten Ecosystems

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Soils are hugely important to human life.  Do you like to eat?  Topsoil, the top layer of soil, is the nutrient rich medium where we grow most of our crops.  Nowadays it is possible to grow crops without soil, using hydroponics, but the vast majority of our food and cash crops are grown in soil.  Enjoy not being flooded?  Soils, with their many air-filled pores, have the capacity to absorb large amounts of water, which prevents floods from happening every time it rains.  And after soil absorbs rainwater, it filters it as the water slowly percolates down to the water table, making it safe to drink.  How about having a house?  To this day, many places in the world still use mud and clay as material to build their houses.  This stuff works perfectly: walls made of soil are cool in the summer and warm in the winter (walls made of concrete do the opposite).

Soils are also important as habitat.  They are home to a great diversity of organisms.  In fact, there are a greater number of species (mostly microbes) in one cubic foot of soil than in the entire Amazon rainforest.  These organisms play a vital part in the circle of life.  The majority of soil organisms are decomposers.  They take dead plant and animal matter and break it down as they use its energy to live.  Without these soil organisms, we would be buried under miles and miles of undigested organic matter.

So what exactly is this amazing ecosystem made of? Soil is a matrix of gas, liquid, and solid.  The solid component of soil is made up of mineral particles and organic matter.  The mineral particles are separated into three categories based on particle size: sand, silt, and clay.  Sand particles are the largest, clay particles are the smallest, and silt is whatever falls in between.  Clay particles are so small that one handful of clay has more particles than there are people on the planet.  Different combinations of amounts of the three particle types yield different soil textures.  For instance, a clay soil has some sand and silt, but is mostly clay.  A loam is the holy grail of soil textures.  It has the perfect proportions of sand, silt, and clay.  No matter the kind of particle, there are spaces between them called pores.  Some of the pores hold liquid water, while others hold air.  The fact that there is air and water in soils makes it possible for bacteria, fungi, and plant roots to survive underground.  The texture of the soil determines the size of the pores and their ability to hold water.  Because of this, soils are classified largely by texture.  The broadest category is a soil order, and there are 12 defined soil orders worldwide.

So, as you can see, soils are important and soils are cool.  Soils provide us with many ecosystem services and serve as diverse habitats.  Soils do not deserve to be forgotten.

If you would like to dig deeper into the topic of soils, check out these links:

There is also an awesome documentary about soil called “Dirt! The Movie” (its free on Hulu).

Elizabeth Perkus is a freshman in the College of Agriculture and Life Sciences. She may be reached at [email protected]. The Missing Link: Food & Ag appears on Wednesdays.

Original Author: Elizabeth Perkus