Section 7: Agriculture (Soils, Pesticides, Fertilizers and Land Use)
SOIL BASICS:
BENEFITS OF SOIL: (click below)
Soil Horizons
O Horizon
The letter 'O' stands for organic. As the name suggests, this horizon is rich in organic material of plant and animal origin. These materials are generally in various stages of decomposition. This decomposed organic material is called the humus that gives this horizon its characteristic dark color.
A Horizon
This is also known as the 'topsoil', and it is the topmost layer of the mineral soil. However, as it lies just below the O horizon, this layer also has some amount of humus in it. Hence, it is darker in color than the layers lying below it. This layer is also known as the 'biomantle' as it is the A horizon in which most of the biological activities take place. Soil organisms like earthworms, fungi and bacteria are mainly concentrated in this layer. The soil particles in this region are smallest and finest as compared to the lower horizons of the soil.
E Horizon
This layer lies below the A horizon and above the B horizon. It is light in color and contains mainly sand and silt. It is poor in mineral and clay content as these are lost to the lower layer by the process of leaching. Hence, this horizon is also called the layer of eluviation (leaching).The soil particles of this layer are larger in size than those in the A horizon but smaller than those in the underlying B horizon.
B Horizon
This is referred to as the 'subsoil'. This lies just below the E horizon and is rich in clay and minerals like iron or aluminum. Though this layer has a higher mineral content than the topsoil, some organic material may reach this layer from the layers above by the process of leaching. Plant roots may reach this layer. However, the B horizon is reddish or brownish due to the oxides of iron and clay.
C Horizon
This layer is also known as regolith. The C horizon is mainly made of large rocks or lumps of partially broken bedrock. This layer is least affected by weathering as it lies deep within the soil and is inaccessible to the soil-forming agents. Hence, the rocks in this layer have changed very little since their origin. Plant roots do not reach so deep down to this layer. The C horizon is typically devoid of organic matter.
R Horizon
This is the bedrock. It is the deepest soil horizon in the soil profile. Unlike the above layers, this horizon does not consist of rocks or even boulders. It is made of continuous mass of bedrock. Digging through this layer is very difficult.
Pesticides:Pesticides are chemicals that we use to kill undesireable organisms.
The Need for Pesticides
1. Make our lives easier.
For instance, (using some of our earlier examples) the pesticides in wool and our wood makes our clothes and furniture last longer. You wouldn't want to have to buy a new wool sweater every year, would you?
2. To feed people.
The world population is 7 billion and growing. Of those, 900 million are undernourished. Even with the use of pesticides, over one-third of our food is lost to pests. (Without pesticides, the losses will probably be even higher).
3. Stop diseases.
Many pests transmit diseases which are very dangerous to us.
For example, In the past, malaria was once a serious disease that killed millions of people globally. (The photo to the right shows the red blood cells of someone with malaria.) To fight this problem, we used the pesticide DDT, to kill the mosquitoes which transmitted the disease. It was successful, and the number of people who died from malaria shrank drastically. (More on this later.)
Millions of people in the US. have allergic reactions to the cockroaches in our homes. The pesticides in insect sprays and baits help reduce this problem.
Dangers of Pesticides
1. Toxicity in humans
Genetic damage, reproductive problems, and possible links to cancer are just some of the risks associated with pesticides.
They get runoff and get into the water supplies.
Erosion:
http://blog.alextiller.com/_blog/Alex_Tiller's_Blog_on_Agriculture_and_Farming/post/9_Simple_Methods_to_Control_Erosion_on_the_Farm/
Controlling Erosion
1. Plant a "cover crop" when you're not using the soil.
2. Plant trees around your growing area.
3. Till less! This means the less you dig into the soil, the more resistant it will become to eroision.
4. Grow crops in a contour patter. See above photo
5. Know your biome including precipitation and soil.
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