Plant Water Uptake, Soil Types, Microorganisms, Wheat & Erosion
Plant Water Uptake
The topic of the lecture is: the uptake of water in plants. All plants need water that they get from the soil. Water from the soil is taken in through the root hairs. Root hairs are near the root tip. A healthy crop plant has millions of root tips. The uptake of water is due to a suction pull that starts in the leaves. Water transpires from the cells in the leaf. As water transpires, more water is drawn from the xylem tubes. These tubes extend from the leaves to the root tips. In these tubes the water is stretched like a tight piece of string or wire. Due to the pull of water in the xylem tubes, water is transferred through the root cells to the root hairs. Water is absorbed into the roots and then up to the leaves. A plant does not take an equal amount of water every day or every hour, but we can say that the greater the rate of transpiration, the greater the amount of water the plant takes in. That is to say, the more water a plant loses through the cells in its leaves, the more it absorbs from the soil. The first reason for reduced water uptake is when there is not enough water in the soil. Note this down as shortage of water. The second reason is when there is not enough oxygen for the roots to breathe properly. Note this down as lack of oxygen for root respiration. This happens when the soil is waterlogged, that is to say, when there is far too much water in the soil. The third factor affecting water absorption happens when there are too many salts in the soil water near the roots of the plant. Note this down as high concentration of salts in the soil water near the roots.
Types of Soil
The lecturer will speak about soils all over the world. The title she suggests is types of soil. They can be grouped into four broad classes.
Podzolic Soils
The first type of soil is Podzolic. These soils are mainly found in cool moist climates, climates that you find, for example, in Northern Europe and Canada. These soils were formed under coniferous or partly coniferous forests. They are grey in colour because most of the ion and other minerals have been washed away. They are acid. They have an upper layer of partly decayed plant matter. Below there is a mineral layer with little organic content. For this reason, agriculturally, these soils are very productive. This is so because they are less acid and they allow soil organisms to flourish.
Latosol Soils
Latosol soils are found in countries like Brazil, West and Central Africa and South East Asia (Thailand or Malaysia, for example). They are typical of rainforests. In these areas the climate is hot and humid. An important characteristic is that they are very porous. For this reason, water can easily flow through it. As a result, plant nutrients are washed out and these plant nutrients are needed for agriculture. In colour, these soils are usually red or yellow.
Chernozemic Soils
Chernozemic soils are black or dark brown. These soils are found in parts of Africa, the Soviet Union, the United States, India and parts of South America. These soils were formed under various kinds of grasses, not forests. Concerning agriculture, they are extremely fertile, very good for agriculture.
Desert Soils
There are various types of desert soils. These soils are light in colour. They were formed in arid, that is to say dry, parts of the world (like the Sahara Desert in Africa). As a result, these soils have no organic matter, but desert soils do have a lot of minerals in them. Agriculture may be possible provided that you have proper irrigation, water, in other words, running in ditches through the fields.
Soil Microorganisms
We are going to analyze another aspect of the soil. And so we shall have a look at soil microorganisms. There are millions and millions of very small organisms in every gram of fertile soil, not just millions actually, but thousands of millions. There are five main groups of these microorganisms.
Bacteria
Bacteria are the most numerous group, that means there are more of them, more bacteria than other groups. Bacteria are also the smallest organisms, the smallest that is with one cell, they are single-celled. Most bacteria feed on organic matter. They also break the organic matter down. They get their energy from carbohydrates like sugar, but they also need nitrogen to build cell proteins. Farmers must remember that if they cannot get this protein from the organic matter in the soil, they’ll get it from somewhere else, from the fertilizer that you put on the land, for example. That is the used nitrogen from the fertilizer. Hence the next crop will suffer from a shortage of nitrogen, unless you use extra fertilizer. Bacteria are most active in soil that is warm, damp and well aerated but also not acid.
Fungi
Fungi are really plants although they are very simple types of plants. They break down the lignified tissues. They feed on and break down organic matter. In arable soils, fungi are usually quite small, but in other kinds of soils they can be much larger. A mushroom is an example of a fungus. Fungi differ from bacteria in that they can live in acid conditions; they can also live in drier conditions than bacteria. Some fungi produce diseases in crops, for example, in cereals such as wheat.
Actinomycetes
Actinomycetes have very much the same kind of effect on the soil as bacteria and fungi; they need oxygen to grow. They are common in drier, warmer soils. They are not as numerous as bacteria or fungi. When they are present, they can sometimes cause diseases to plants, for example to potatoes. The disease is at its worst in light, dry soils.
Algae
Algae are very small and simple organisms. Since they contain chlorophyll, they can build up their bodies by using carbon dioxide from the air and nitrogen from the soil. Algae grow well in damp soils exposed to the sun. They can also grow in waterlogged soils. Here they can be helpful because they use dissolved carbon dioxide from the water and then release oxygen. This process is important for crops such as rice.
Protozoa
Protozoa are single-celled like bacteria, they are actually animals; very, very small animals, but still animals. Most protozoa feed on bacteria. Some protozoa contain chlorophyll. Therefore, they can produce carbohydrates.
Wheat
One of the main cereal crops of the world is rice. Another important cereal crop is wheat. Its Latin name is triticum aestivum. This cereal is adapted to harsher environments than rice. It mainly grows in prairies. Prairies are large mainly flat areas of land. They are found in the United States and Russia. Prairies are windswept and too cold and dry. The main producers in the world are the Soviet Union with about 23.7% followed by the United States with about 15.1%. They are followed by Canada and France with 4.8%. Other producers are: India with 4.4%, Italy with 3.8%, Turkey with 3%, Australia with about 2.8%, Argentina with about 2.8%. A primitive kind of wheat was used in Iraq some 9 thousand years ago. It was used in Egypt about 5 thousand years ago. We do not know when people began to use wheat to make bread. The Egyptians made bread from wheat about four thousand five hundred years ago. Bread is made from two types of wheat; firstly, there is hard wheat and, secondly, there is soft wheat. Hard wheat has more proteins in it. It is used to make the best formed bread and also bread that lasts longer. Soft wheat is starchy. It is used to make pastries or bread that is eaten quickly. Wheat can also be classified into winter and spring types. Winter type is sown in winter so that they can get up to a good start before the freezing weather section. They can live through temperatures below freezing particularly if they have a covering of snow to protect them. Winter wheat crops are ready for harvesting in the early summer. Spring types are sown in the spring in more northerly parts of the world. They are adapted to a short growing season, sometimes as short as ninety days. They give a satisfactory crop.
Soil Erosion
The lecture is soil erosion. What is erosion? The loss of soil, more exactly, the loss of topsoil. Soil erodes due to the action of two main agents: water and wind. Erosion affects more severely farmers in the tropics facing tropical agriculture today. The loss due to erosion amounts to 250 tons of topsoil per hectare every year. This amount is higher in areas where there is a lot of rain, heavy rainfall and where the slopes, or sides of the hills, are bare. If there are trees on the side of the hill, erosion can be reduced to as little as 1% even with the same amount of rain. The severity of erosion depends on five main things. The first factor is the slope itself. Erosion begins when the slope is less than one degree. Erosion becomes very serious when the slope is more than six degrees. The second factor is how much vegetation, trees, bushes and so on, there are on the slope. The roots of trees and other plants hold the soil together. If trees are cut, you’ll get more erosion. The next factor is soil type and humus content, how much humus there is in the soil. Dry, light soils that don’t have much humus in them, don’t hold together so well as, for example loams, so they are more erodible. Erosion also depends on the use we make of the soil, cultivation in other words. If we leave large areas of bare soil on our land, we’re more likely to get erosion. So large areas of bare soil should be avoided. The last factor is climate, something we can be aware of but we can´t make much about it. We should remember that rain faster than ten millimeters an hour is dangerous. On the other hand, light rain is obviously useful. This often happens in the first one or two storms of the season.