Water is held in the soil in two main ways - Leaving Cert Agricultural Science - Question 2 - 2017

1. Lowering Water Table: Artificial drainage helps manage the water table by reducing excess water in the soil. This prevents waterlogging, which can hinder root development and crop growth.

2. Improved Crop Yield: By controlling the soil moisture through drainage, farmers can cultivate crops more effectively. This leads to healthier plants and ultimately increases crop yield due to reduced disease risk and enhanced nutrient availability.

1. Leaching of Calcium: Rainfall can lead to the leaching of calcium ions ($ext{Ca}^{2+}$) from the soil, which reduces the neutralizing capacity of the soil and increases acidity.

2. Use of Acidifying Fertilizers: Fertilizers that contain ammonium or other acid-forming elements are incorporated into the soil. When these fertilizers decompose, they release hydrogen ions, contributing to increased acidity.

3. Decomposition of Organic Matter: Organic matter breaks down over time, releasing acidic components that lower the pH of the soil. This can be exacerbated by the presence of acidic manures.

1. Leaching Mechanism: As rainfall occurs, soluble calcium ions ($ext{Ca}^{2+}$) are washed away from the soil horizon into deeper layers or out of the root zone entirely. This reduction in base cations diminishes the soil's buffer capacity, leading to an increase in acidity.

2. Fertilizer Decomposition: Fertilizers that release ammonium undergo nitrification, which converts ammonia to nitrate. This process generates hydrogen ions ($ ext{H}^+$$), thus increasing soil acidity as these positively charged ions displace the base cations, making the soil more acidic.

3. Organic Matter Decomposition: As organic matter decomposes, it produces organic acids. These acids lower the pH of the soil, increasing the overall acidity and reducing the availability of some nutrients.

1. Poor Nutrient Uptake: Increased soil acidity can hinder the availability of essential nutrients such as phosphorus and potassium. Crops may struggle to absorb these nutrients effectively, leading to stunted growth and poor yields.

2. Inhibition of Nitrogen Fixation: Higher acidity levels can affect the viability of nitrogen-fixing bacteria in the soil, reducing their activity. This can limit the availability of nitrogen for plants, further affecting growth and productivity.

To demonstrate cation exchange, you can set up a simple laboratory experiment:

1. Materials Needed: Soil sample, KCl solution (for leaching), and ammonium oxalate.

2. Procedure:

   • First, wash a soil sample with KCl solution to saturate it with potassium ions ($ext{K}^+$).
   • Then, leach the sample with ammonium oxalate solution to wash out the calcium ions ($ext{Ca}^{2+}$) that will be replaced by potassium ions.
   • A white precipitate will form indicating the presence of calcium oxalate if Ca²⁺ is present.

3. Observation: If the resulting solution turns positive for potassium when testing with sodium cobalt nitrate solution, a positive color will indicate successful cation exchange.