The soil is a complex mixture of mineral and organic materials, which interact with one another. Soil can be shallow to very deep, but the surface of the soil also known as topsoil is what I want to focus on. Topsoil is soil consisting of various mixtures of sand, silt, clay and organic matter; considered to be the nutrient-rich top layer of soil that supports plant growth. Topsoil is critical in producing good crops. It is in the topsoil where most of the natural soil fertility is found. It can take more than a hundred years to produce 2.5 cm of topsoil, but poorly managed fields can lose this amount in just a year or two.
You can learn a great deal about your soil just by looking at it. In this broadcast I want to tell you about some the physical properties of soil and how this can be used to learn about the soil. Soils, like all physical bodies, have unique properties that define them. There are seven physical properties that we look at when diagnosing if a soil is healthy or not, or to tell one type of soil from another. These include: color, texture, tilth, water holding capacity, drainage, depth, and slope. I will discuss each of these properties separately, but they are also all interrelated.
The Color of a soil can give clues to its health, origin, and long-term changes. It can also indicate the color of the parent material. The parent material is the substance from which the soil developed. In my area most the parent material is a mixture of rock. But, parent material could be mud washed in from rivers, sand from desert of coastal regions, or lava from volcanic regions. I just always have to remember that the soil has a parent just as we all do.
Let me tell you a story about my parents. I grew up on a farm that produced both grain and livestock. I was able to work with my parents and they taught me a great deal about farming and life. I tried to please my parents, but from time to time I would disappoint them and I felt terrible. Jesus tells a story about a parent and his sons by saying: “There was a man who had two sons. The younger one said to his father, ‘Father, give me my share of the estate.’ So he divided his property between them. “Not long after that, the younger son got together all he had, set off for a distant country and there squandered his wealth in wild living. After he had spent everything, there was a severe famine in that whole country, and he began to be in need. So he went and hired himself out to a citizen of that country, who sent him to his fields to feed pigs. He longed to fill his stomach with the pods that the pigs were eating, but no one gave him anything. “When he came to his senses, he said, ‘How many of my father’s hired men have food to spare, and here I am starving to death! I will set out and go back to my father and say to him: Father, I have sinned against heaven and against you. I am no longer worthy to be called your son; make me like one of your hired men.’ So he got up and went to his father. “But while he was still a long way off, his father saw him and was filled with compassion for him; he ran to his son, threw his arms around him and kissed him. “The son said to him, ‘Father, I have sinned against heaven and against you. I am no longer worthy to be called your son.’ “But the father said to his servants, ‘Quick! Bring the best robe and put it on him. Put a ring on his finger and sandals on his feet. Bring the fattened calf and kill it. Let’s have a feast and celebrate. For this son of mine was dead and is alive again; he was lost and is found.’ So they began to celebrate.
While the younger son was rebellious against his father, it is the loving father of this story who depicts the heart of the loving Heavenly Father. God the Father longs for the return of the sinner, who willingly grants forgiveness, and who rejoices in the return of the wayward. This father gave the son what he had asked for. He allowed the son to go his own way, even when he could have prevented it. The heart of that father never forgot the wayward son. It was no accident that the father saw the son coming “from a long way off”. The father ran to meet the son. He did not force the son to beg. He did not even allow the son to finish his confession. The father quickly restored the son to his position as a son. The father commanded that there be a celebration. How great the love of this father. How much like the Heavenly Father he is.
When I think about the younger brother, I can see myself. There has been so many times that I have rebelled against God and have found myself coming back to God. I am so glad that my God is just like the father in this story. He always welcomes me back with open arms. If you do not know God he is also longing for you to come to Him. It is my prayer that anyone listening to this broadcast who does not know God will seek Him out. If you do this God will throw his arms around you and love you just as the father in this story.
I have had the opportunity to travel all around the world and I also have a great deal of interest is soil. When I look at a soil the color is the first thing I notice. It can tell me a great deal. Near the surface of the soil I first look to see how dark the soil is. Dark colors in the topsoil usually indicate the soil has a high organic matter content. Organic matter is just the small fraction of the soil, which was once alive. Most organic matter comes from decomposed plants and plant roots. The more organic matter the blacker the soil. Look at your soil and if it has a very dark color and if it very productive, that means it has a high amount of organic matter.
Some soils that I have seen have very little in the way of dark colors. Some soils are red to yellow at the surface. These soils are found mostly in the tropical areas of the world. In these areas the higher temperatures and rainfall has resulted in the rapid decomposition and removal of organic material. These soils are generally not very productive, and require more fertilizer to grow crops.
As I look deeper into the soil I sometimes notice that the soil changes colors as I dig into the soil. Each one of the soil layers that has a distinct difference is called a soil horizon. In some soil horizons the color is mostly red. This is an indication of well-drained soil, where as gray soils indicate poorly drained or wet soils. The soil has a large amount of iron in it. When iron is exposed to air it rusts and turns red. This is the same process that takes place in the soil. In some soil horizons I find both red and gray. This indicates a soil that is dry during a portion of the year and wet at other times.
Using color can be a great way of better understanding your soil. If you find a soil that has a red topsoil and red soil in deeper soil horizons, would you plant rice or would you plant beans? The beans would be the better choice, because it would be hard to maintain a flood for rice production.
The next physical property I want to discuss is called soil texture. Soil texture refers to the relative proportions of sand, silt, and clay in a soil. A soil's texture has a big influence on its productivity and management needs because it affects water movement. To get a general idea of a soil’s texture, take a small amount of topsoil, moisten it, and rub it between your fingers and thumb.
In order to determine the soil texture by feel, the soil must be moistened. Add a small amount of water until the soil is moist but not muddy. You want to be able to move the soil about between your thumb and forefinger. In doing this, you are feeling if the soil is gritty, sticky, or smooth, which are the "feel" characteristics for sand, clay and silt, respectively.
After you have worked the soil, you try to extrude the soil between your thumb and forefinger to stretch the soil; the longer you can stretch the soil, the more clay in the soil.
Soils with a lot of sand will fall apart, while those with more clay will eventually be able to be worked into a very long piece of soil, which is greater than 5 centimeters long. Silty soils feel very smooth. Eventually, after much practice, you will be able to get pretty good at determining what the soil texture is
Tilth refers to a soil's physical condition. A soil in good tilth is easily worked, is crumbly, and readily takes in water when dry. Factors that influence a soil's tilth include: texture, organic matter, and moisture content.
Therefore, tilth can vary markedly with changes in moisture content, the amount of organic matter present, and compaction. Tilth can be improved, which is why farmers plow their fields to break up the clods and add manure to their fields when they can.
About half of a soil's volume is pore space that is occupied by varying amounts of air and water, depending on how wet the soil is. This ability of a soil to store and hold water is called the soil’s water holding capacity. Water is held in the pore spaces in the form of films adhering to the soil particles. Small pores are called micropores, while large pores are called macropores.
Macropores do not hold water well because the water films become too thick to adhere well to the surrounding soil particles. This water is lost downward as it drains below the root zone by gravity. So, macropores allow a soil to retain enough air for root growth, as long as drainage is not impeded.
The films of micropore water, however, resist being drained away by gravity and are responsible for the water-holding capacity of soils. This water is what the roots can tap into and extract for plant use. As you may guess, sands have a lot of macropores due to their large grain size but few micropores. Thus, their water-holding capacity is low although their drainage is good. Clay soils that have a lot of micropores may have a higher water-holding capacity, but because they have fewer macropores, their drainage is poor. Plants really like a soil that lies in between these two extremes so that their roots have both the air and water that they need.
Drainage refers to a soil's ability to get rid of excess water, or water in the macropores, through downward movement by gravity. It is affected by topography, texture, and tilth. With few exceptions, one would be a crop like rice; most plants need fairly good drainage. Without good drainage, plant roots would lack oxygen, nitrogen would be lost, and certain elements like iron and manganese may become soluble enough to injure plant roots. Although clay soils are more likely to have drainage problems, drainage problems also occur on other soils where the water table is close to the surface. The water table is the upper surface of the ground water below which the soil is completely saturated with water. Soil color can be affected by drainage. Soil color can be a tool to check if your soil is having drainage problems.
Soil depth refers to how deep, top to bottom, the topsoil plus the subsoil is. Depth can be easily determined by digging a hole. Soils are classified as being deep or shallow as follows: Deep = 1 meter; Moderately Deep 0.5 to 1.0 meters; Shallow 0.25 to 0.50 meters; and Very Shallow less than 0.25 centimeters. Soil depth is important for plants because deeper rooting means more soil to explore for nutrients and water. Greater soil depth can also mean better drainage, as long as there are no restrictive layers in the subsoil.
A field's slope has a marked influence on the amount of water runoff and soil erosion caused by flowing water. Slope is usually measured in terms of percentages. A ten percent slope has ten meter of vertical drop per 100-meter horizontal distance. Soil conservation measures become necessary on land with as little of a slope as 1-2% to avoid erosion problems.
The physical properties are very complicated and I was only able to share a brief introduction of these properties. In contrast, God’s love for you is very simple. He loves you as a parent loves their child. God is my heavenly Father, and if you do not know him as your heavenly Father I pray that He will soon be yours.