Have you ever noticed the colour of the water in a river or stream after a heavy rainfall？What do you think caused this change in colour？It is soil that has been washed into the river from the riverbank or from the nearby fields．
你注意过大雨后小河小溪中的水的颜色吗？你认为是什么导致了颜色的变化？是从河岸还是附近田野冲到河里的土壤。
Components of Soil
土壤成分
Soil is made up of a number of layers, each having its own distinctive colour and texture. The upper layer is known as the litter. It acts like a blanket, limiting temperature changes and reducing water loss. The topsoil layer is made up of small particles of rock mixed with rotten plant and animal matter called humus, which is black and gives the topsoil its dark colour. This layer is usually rich in nutrients, oxygen, and water. Below the topsoil is the subsoil, a layer that contains more stones mixed with only small amounts of organic matter. This layer is lighter in colour because of the lack of humus. Beneath the soil lies a layer of bedrock．
土壤由多层组成，每一层都有自己独特的颜色和质地。上层被称为表土层，它起到地毯的作用，限制温度变化，减少水分流失。表土层由岩石的小颗粒与腐殖质混合而成，腐殖质是黑色的，使表土呈深色。这一层通常富含养分、氧气和水。在表层土下面是心土，这一层有较多的石头和少量有机物。由于缺乏腐殖质，这一层颜色较浅。土壤下面是一层基岩。
Soil forms from the bottom up. Over time bedrock is attacked by rain, wind, frost, and snow. It is gradually broken down into smaller particles in a process called weathering. Plants begin to grow, and rotten materials enrich the topsoil. Most of the soil in Eastern Canada, for example. Was formed from weathered rock that was exposed when the ice disappeared 12,000 years ago．
土壤是自下而上形成的。随着时间的推移，基岩会受到风霜雨雪的侵蚀。在风化过程中，逐渐分解成更小的颗粒。植物开始生长，腐烂的物质会使表土层更加肥沃。例如，加拿大东部的大部分土壤是由12000年前冰消失时露出的风化岩石形成的。
Water Beneath the Soil
土壤地下水
Surface water collects and flows above the ground in lakes, ponds, and rivers. Once in the soil or rock, it is called groundwater. Gravity pulls groundwater through the soil in a process called percolation. Eventually the water reaches a layer called the water table. Under this is bedrock through which water cannot percolate.
地表水在地面以上的湖泊、池塘和河流中聚集和流动。一旦进入土壤或岩石中，则称为地下水。重力将地下水从土壤中抽取出来的过程称为渗透。最终，水进入地下水位层。在这个层下面是基岩，水不能通过它渗透。
As water percolates downward, it dissolves organic matter and minerals from the soil and carries them to deeper layers. This causes a serious problem because plants require these nutrients for growth.
当水向下渗透时，它会溶解土壤中的有机物和矿物质，并将它们带到更深的土层。这会导致一个严重的问题，因为植物生长需要这些养分。
Soil pH
土壤pH值
Soil can be acidic, neutral, or basic. The pH of the soil is determined by the nature of the rock from which it was formed, and by the nature of the plants that grow and rot in it．
土壤可以是酸性、中性或碱性。土壤的pH值取决于形成土壤的岩石的性质，以及在其中生长和腐烂的植物性质。
The acidity of rain and snow can lower the pH of the groundwater that enters the soil. By burning fossil fuels such as coal, oil and gasoline, humans have been contributing to higher levels of acidity in many soils. When fossil fuels are burned, gases are released into the air and then fall back to earth as acid rain. Acid soil increases the problem of carrying nutrients to lower soil levels. As nutrients are removed, soil is less fertile. Plants grow more slowly in acidic soil, and also become easily attacked by diseases.
雨雪的酸度会降低进入土壤的地下水的pH值。通过燃烧煤炭、石油和汽油等化石燃料，人类一直在提高许多土壤的酸度。当燃烧化石燃料时，气体会释放到空气中，然后随着酸雨落回地面。酸性土壤会增加将养分输送到较低土壤水平的问题。随着养分的流失，土壤变得不那么肥沃。植物在酸性土壤中生长较慢，也容易受到疾病的侵袭。
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