4.2: Why Soil Health Matters pg. 130
Key Concepts:
1. Some ecosystems are designed, created, and maintained by humans.
2. It is important to keep Earth’s soil healthy.
Components of Soil
There are four main components of Soil. a) Minerals: minerals are formed when wind, water, chemicals, and living things gradually cause rock to break down (erode) into tiny particles b) Organic Matter: small bits of organic matter found in the soil is called Humus. Humus is produced by the decay and waste produces of living things. Humus provides nutrients that plants will used to grow. c) Air: the minerals and humus have air spaces between them known as spores. Air can be found in the spaces. d) Water: is also found in the pores between the minerals and humus of the soil.

Other than plants, soil also supports other organisms. In soil there are also fungi, insects, worms, and bacteria.
These organisms are responsible for decomposing organic matter, keeping the soil loose and well mixed.
Figure 1: The bacteria, fungi, worms, and insects in soil male nutrients available to plants.

Managing Soil
If the ecosystem is being engineered, then the soil needs to be maintained.
Soil Nutrient Cycles
Nutrients, amount and availability are the most important factors to be maintained, to keep the soil healthy. Nitrogen, phosphorus, and potassium are very important to plant health. These nutrients are cycled through a natural ecosystem by producers (plants), consumers (animals), and decomposers.
On farms there is a problem, the nutrients that need to be recycled are removed when the crop is harvested. Soil nutrients eventually run out and cannot support plant growth.
Figure 2: Nutrients move through farmlands much differently than through natural ecosystems. In this illustration, the nutrients are shown as arrows.

Fertilizers
Fertilizer: a substance applied to an area to provide the nutrients plants need for growth.
Natural Fertilizer: plant nutrients that have been obtained from natural sources and have not been chemically changed by humans.
Synthetic Fertilizer: plant nutrients that are produced by subjecting natural materials to chemical processes.
Farmers replace lost nutrients by using fertilizers, this replaces the nitrogen, phosphorus and potassium. Natural fertilizers like; manure and seaweed were used until the early 1900’s. Natural decay processes broke down the organic matter releasing nutrients into the soil for plants to use.
Synthetic fertilizers are manmade. They contain nutrients, which are released through natural processes. These fertilizers are easy to use, they can be sprayed or spread on the fields. The nutrients are available right away to the plants. Synthetic fertilizers were used often by the 1960’s.

Environmental Impact of Fertilizers
Fertilizers are both good and bad for the environment. The greatest problems occur with synthetic fertilizers.
Fertilizers enter the soil quickly and cause the type of organisms to change. Less organic matter is present therefore there is less nutrients available. The recycling of organic matter and nutrients is altered.
Leaching occurs during heavy rain or the spring thaw.
Nutrients are washed away into streams, rivers, and lakes.
The nutrients that enter the aquatic environment have a negative impact on the aquatic organisms. There are increases in algae growth, creating an algae bloom, which decrease the waters oxygen content. The lack of oxygen will kill will lead to the death of other organisms.
Controlling the Flow of Water in Soil
Crops require a large amount of water to grow, farmers will water their plants quite frequently, and this is called irrigation. Farmers need to control the water flow in their fields especially the drainage. The water supply for the crops, usually come from surface sources like, lakes, ponds, or rivers.
Taking water form lakes, ponds, wetlands can lead to a water shortage and damage habitats and wildlife. These water sources can also be damage by field run off.

Soil Needs Space
Soil must be loosely packed, allowing for air spaces, where water and soil nutrients can be found. Plant roots will absorb the water, dissolved nutrients and oxygen.
Alternative Farming Practices
No-tillage Farming – Farmers will leave their land undisturbed after a crop harvest. This will help the soil retain nutrients and improve soil quality.
Crop Rotation – Farmers will plant one type of crop in a given area one year and then plant a different type of crop for the next year. This practices helps to maintain soil nutrients and requires less amount of fertilizer.
Crop Selection – Farmers will grow on crops that are more suitable to the local growing conditions. This can reduce or eliminate the need for irrigation and fertilizer.

Check Your Learning:
Questions 1 – 10, pg. 134
Wrap Up:
- Healthy soil is vital to plant growth.
- The four main components of soil are minerals, organic matter, air, and water.
- Soil nutrient cycles are different in engineered ecosystems than they are in natural ecosystems.
- Lost nutrients can be replaced by applying synthetic or natural fertilizers.
- Fertilizers can cause problems for the environment.
- Farmers change the natural locations of water supplies when they add or remove water from their fields.
-Soil compaction can reduce the ability of soil to support life.
- Practices such as no tillage farming, crop rotation, and crop selection reduce the impacts of agriculture on soil health.