Lesson Notes By Weeks and Term v4 - SHS 3
AGRICULTURAL MACHINERI ES
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AGRICULTURAL MACHINERI ES
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Agricultural Science
Class: SHS 3
Term: 1st Term
Week: 10
Grade code: 3.1.3.LI.2
Strand code: 1
Sub-strand code: 3
Content standard code: 3.1.2.CS.2
Indicator code: 3.1.3.LI.2
Theme: NEW DAWN AGRICULTURE
Subtheme: AGRICULTURAL MACHINERI ES
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In Ghana, our agriculture is heavily dependent on rainfall, which is becoming increasingly unreliable due to climate change. The long dry season (Harmattan) often halts farming activities, leading to food shortages and reduced income for farmers. This lesson explores irrigation – the artificial application of water to land – as a crucial technology to overcome these challenges. We will focus on simple, adaptable systems suitable for valuable crops like mangoes, oranges, and cocoa. Understanding how to use irrigation effectively can transform farming from a seasonal activity into a year-round, profitable business, ensuring food security for our communities and nation.
A. What is Irrigation?
Irrigation is the controlled, artificial application of water to soil or land to assist in the growing of crops. Its primary purpose is to supplement natural rainfall, especially during periods of drought or in areas with low precipitation, ensuring that crops receive the adequate amount of water needed for optimal growth and yield.
Importance in the Ghanaian Context: Combats Climate Change: Counteracts the effects of unpredictable rainfall patterns and prolonged droughts. Enables All-Year-Round Farming: Farmers can cultivate crops during the dry season, leading to multiple harvests per year. Increases Crop Yield and Quality: Consistent water supply prevents water stress, leading to healthier plants, larger fruits, and higher overall yields. Enhances Food Security: Reduces our reliance on seasonal harvests and food imports (e.g., tomatoes and onions from neighbouring countries). Improves Farmer Livelihoods: Provides a stable and increased source of income for farming families. B. Types of Simple Irrigation Systems
These are systems that can be adapted by small-to-medium scale farmers in Ghana without requiring massive industrial infrastructure. Drip or Trickle Irrigation Description: This is a highly efficient micro-irrigation system. Water is delivered slowly and directly to the root zone of individual plants through a network of pipes, tubes, and small outlets called 'emitters' or 'drippers'. How it Works: A pump pushes water from a source (borehole, dam, tank) into main lines, which then feed smaller lateral pipes running alongside the rows of trees. Emitters placed near the base of each tree release water drop by drop. Advantages: High Water Efficiency: Reduces water loss through evaporation and runoff (up to 95% efficient). Crucial for Northern Ghana. Reduces Weed Growth: Water is only applied where it is needed, so areas between plants remain dry. Fertigation: Liquid fertilizers can be mixed with the irrigation water and applied directly to the roots, saving labour and fertilizer. Operates on low pressure, saving energy. Disadvantages: High Initial Cost: The cost of pipes, filters, and emitters can be high for smallholder farmers. Clogging: Emitters can easily get blocked by silt or mineral deposits if the water is not properly filtered. Requires technical knowledge for installation and maintenance. Best Suited For: Orchards (mango, citrus, pawpaw), high-value vegetable farms, and plantation crops in their early establishment phase. Sprinkler Irrigation Description: Water is pumped through pipes and sprayed into the air through rotating sprinkler heads, falling onto the crops like artificial rainfall. How it Works: A powerful pump moves water through a system of main and lateral pipes to sprinklers. The pressure of the water causes the sprinklers to rotate and distribute water over a specific area. Advantages: Suitable for a wide variety of soil types and terrains. Can cover a larger area more quickly than drip irrigation. Can be used for frost protection in some climates. Disadvantages: Lower Water Efficiency: A significant amount of water can be lost to evaporation and wind drift, especially on hot, windy days. High Energy Cost: Requires higher water pressure than drip systems, meaning a more powerful (and expensive) pump is needed. Can promote fungal diseases by wetting the leaves of the plants. Best Suited For: Nurseries (cocoa, oil palm), vegetable farms, and closely spaced crops. Less ideal for widely spaced fruit trees compared to drip. Surface (Furrow) Irrigation Description: This is a traditional and widely used method where water moves over the soil surface by gravity. In furrow irrigation, small channels or 'furrows' are dug between rows of crops, and water is directed into these furrows. How it Works: Water is released from a main channel into the furrows. It flows down the furrow and seeps into the soil, watering the roots of the plants on either side. Advantages: Very Low Initial Cost: Requires minimal equipment, mainly labour to dig the furrows. Low energy requirement as it relies on gravity. Simple to operate. Disadvantages: Very Inefficient Water Use: A large amount of water is lost to runoff and deep percolation below the root zone. Requires a level or uniformly sloped piece of land. Can lead to soil erosion and waterlogging if not managed properly. Uneven distribution of water (plants at the start of the furrow get more water than those at the end). Best Suited For: Row crops on flat land with access to a large, cheap water source. Used in some government irrigation schemes in Ghana (e.g., for maize and rice), but less ideal for valuable tree crops. C. The Extent of Adaptation in Ghana