In last week’s study guide (week 26), guide author Cáit McEllistrem set students a number of questions as part of the student activities. Please find answers below:

Explain what is meant by the term pH?

It is a measure of how acidic or basic a substance is (the concentration of hydrogen ions in a solution). It goes from 1 to 14.

  • pH7 =neutral.
  • pH1-6 = acidic.
  • pH8-14 = basic.
  • Cathal and Sinéad collected four soil samples from the same location and tested the pH of each sample. The results are presented in the table below:

    A. The actual pH of the soil sample was 6.0. State with a reason who was most accurate in their analysis of the soil samples.

    Sinéad’s, her average (show calculation) is closer to the true answer.

    B. Place a tick in the correct box which illustrates the optimum pH level for crop growth:

    C. Identify two issues that may affect crop growth in soils when either a very low- or a very high-pH (ie, below 5.5 or above 8.5) is present.

    • 1. Reduced availability of nutrients to plants resulting in reduced yield.
      • 2. Has an impact on the microbiome in the soil leading to unsuitable environmental conditions. This may lead to lower yield.
      • 3. Name three methods of spreading inorganic fertiliser.

      • Broadcast.
      • Placement.

    • Top dressing.
    • 4. What is a cation and name two examples.

      Cations are positively charged nutrients such as calcium and nitrogen which will stick on to negatively charged anions in the soil such as clay and humus.

      Examples include: hydrogen, potassium, calcium, magnesium and aluminium ions. (H+, K+, Ca2+,Mg2+,Al3+)

      5. In what type of plant tissue do the nutrients travel throughout the plant?

      Xylem.

      6. When is the ideal growth stage for grazing of perennial ryegrass?

      Vegetative stage

      7. Give two examples each for the biological, chemical and physical functions or organic manure.

    • Biological: nutrient reservoir, biodiversity.
    • Chemical: pH buffering, cation exchange.
    • Physical: soil structure, water retention, reduction of soil capping.
    • 8. Describe four benefits of earthworms.

    • They convert organic matter into humus which improves soil fertility.
    • They improve soil structure through burrowing, creating channels that improve and aid aeration and drainage.
    • They mix layers of soil by bringing organic matter to deeper levels through burrowing.
    • Worm casts created by excretion are high in nitrogen, phosphates and potash due to the breakdown of organic and mineral material in the earthworm’s digestive system. This leads to higher nutrient levels in the soil.
    • 9. Calcium is drawn from the bloodstream to make milk. Calcium has many functions in the cow’s body. Name a deficiency disorder of calcium and explain how the symptoms of this disorder are linked to the functions of calcium in the body.

      Milk fever: reduced blood calcium levels due to insufficient calcium in the diet. Most common in first few days of lactation when demand for calcium for milk production exceeds the body’s ability to mobilise calcium reserves. Prevention: make sure cattle are at a BCS 3.35. Magnesium supplement (mineral lick) promotes calcium metabolism and mobilisation.

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