Unit B: Sustainable Ecosystems
4.2: Managing the Soil-Controlling the flow of Nutrients and Water
pg. 123
Key Concepts:
2. Agricultural practices alter natural biogeochemical cycles.
3. Agricultural practices alter water cycles.
- The soil is our most important resource.
- Formers require fertile soil to grown their plants.
- Plants use soil for support, water, nutrients, air and decomposition of dead
matter.
- Many different organism and micro-organisms live within the soil.
Managing Soil Nutrients
- In farms or agroecosystems, the natural nutrients and water cycles are
disrupted.
- Plants used water and take up nutrients from the soil.
- When plants are harvested, the nutrients are removed from the ecosystem.
- Even with livestock nutrients are not returned.
- Soil becomes depleted of nutrients and can no longer support grow.
Figure 2: In agroecosystems, many nutrients (shown here as arrows) are
added to the soil as fertilizers. Nutrients are taken up by plants and removed
from the agroecosystem when we harvest the crop. After we eat the crop,
some of the nutrients end up in our waste disposal system.
Natural and Synthetic Fertilizers
Natural Fertilizer: plant nutrients that have been obtained from natural
sources and have not been chemically altered by humans.
Synthetic Fertilizer: fertilizers that are manufactured using chemical
processes.
- Farmers add nutrients to the soil by using natural and or artificial fertilizers.
- Natural ecosystems recycle their nutrients, and are healthy and sustainable.
- Artificial ecosystems lose their nutrients, farmers harvest their crops and
the nutrients are removed, not recycled. We mow our lawns and collect the
grass clippings.
- Synthetic fertilizers were introduced in the 60”s, and quickly increase crop
yields and profitability.
Environmental Impacts of Fertilizer Applications
- Fertilizers can negatively impact both terrestrial and aquatic ecosystems.
- Synthetic fertilizers when used can stress the natural soil community.
- Synthetic fertilizers breakdown quickly and enter the ground water.
- Leaching is a natural process where water dissolves minerals and removes
them from the soil, including fertilizers.
- If these nutrients should enter our drinking water, there can be detrimental
to our health.
- When nutrients enter aquatic ecosystems, an increase in algae growth will
occur.
- The result is an Algal bloom. Algae grow, die and decompose.
- Bacteria decompose the algae. During this process oxygen is greatly
consumed.
- Aquatic organisms die because of the lack of oxygen.
- Natural fertilizer is less concentrated and release nutrients gradually, while
synthetic fertilizers are the opposite.
Table 1: Advantages and Disadvantages of Using Synthetic and Natural
fertilizers
Examples
Synthetic Fertilizer
Ammonia, synthetic urea,
potash, potassium,
commercial chemical
fertilizers
Natural Fertilizer
Animal manure, sludge, plant
materials, such as; seaweed
and compost, blood meal,
bone meal, wood ashes
Advantages
Disadvantages
Controlling the Flow of Water in Soil
- To grow crops and raise livestock a large supply of water is required.
- Water from rivers, lakes, and ground water supply these farms.
- Irrigation systems are developed to divert water to where it is required,
drainage is used to convert wetlands into fertile farmland.
- Altering water levels has a negative affect on the ecosystem. Aquatic
ecosystems are harmed and water shortages occur, droughts.
Soil Air Spaces and Compaction
- Air spaces in the soil perform two purposes; allow water and oxygen to
enter the soil and travel to the roots of plants.
Alternative Farming Practices
- There are three alternative farming practices that protect the soil;
a) no-tillage
b) crop rotation
c) crop selection
BLM: 4.2-1: Try This: Compare Synthetic Fertilizers and Natural Fertilizers
Awesome Science: Black gold
BLM: 4.AS-1
Evidence of Learning: Students can …
- understand how human activity in agroecosystems can change natural
environments.
- understand how agriculture can impact the sustainability of an ecosystem.
Check Your Learning
Questions 1 – 8, page 128
Summary:
- Fertilizers disrupt biogeochemical cycles and can pollute the environment.
- Synthetic fertilizers cause more ecological problems than natural
fertilizers.
- Farmers alter the water cycle by irrigating fields or using drainage pipes to
remove water.
- Soil compaction limits water flow and harms plants by reducing oxygen
and nutrient.
- Practices such as no-tillage farming, crop rotation, and crop selection
reduce the impacts or agriculture on the soil ecosystem.