描述土壤由什么构成

What would be the ideal type of soil? What properties would such a soil have? Why do you think this? 

The Science Behind the Science

Soil is a mixture of organic matter and inorganic matter that is found on the surface of the Earth. It isn’t something that we usually think about and we are often surprised at the complexity of it. Soil itself can vary in its structure and composition and is vital to the sustainability of an ecosystem because it is the natural medium for growth of vegetation. The inorganic material within the soil isn’t living and includes minerals and weathered rocks. Did you know that weathering is the process in which rocks are broken down into smaller pieces? Once this process is complete, these smaller pieces of rock then mix with organic materials (those of living organisms) to then release nutrients for growth.

There are three different types of soil. Sand is one type that is made from small particles of rock that have undergone the weathering process. The sand itself is loose so that water can easily drain through it, making it excellent for drainage. It is also coarse. Sand isn’t good for growing plants because it cannot hold water or the nutrients that plants need.

Silt is another type of soil and it can be thought of as fine sand. It holds water a lot better than sand does, and is mainly composed of medium-sized particles. This type of soil holds more moisture than sandy soil, and often feels slick and smooth once water has been added to it. 

Clay soil has over 25% clay in it and is fine-grained. The particles in clay soil are even smaller than those in silt, so there is even less space between the grains for both air and water to circulate effectively. This soil type is also known as heavy soil as it does not drain well or provide enough space for roots to grow. Clay holds most water in comparison to the other soils. However, when moisture is added to clay, it is very easily moulded into different shapes and sizes. Clay soil bakes in the Summer and often cracks due to its hardness.  

Although there are three main types of soil, most soils are made from a combination of the three. For example, loam is a combination of sand, silt and clay. Its properties will vary depending on how much of each substance is present within it. For example, you may get sandy loam, silt loam, clay loam, sandy clay loam, silty clay loam, and loam. This type of soil usually contains a lot more nutrients and moisture which is necessary for better drainage and infiltration of water and air. Loam soil is suitable for growing pretty much all plant varieties.  

Mission Assignment Information
The sand should have the lowest water holding capacity, the clay should have the highest water holding capacity. The loam should be somewhere in the middle with a darker colour than both the clay and the sand. This indicates that this type of soil contains a lot of nutrients.