Problem 210 - A Complete Resource Book in Chemistry for JEE Main

Question

Regular use of which of the following fertilizers increases the acidity of soil? (a) urea (b) super phosphate of lime (c) ammonium sulphate (d) potassium nitrate

Step-by-Step Solution

Answer

(c) Ammonium sulphate increases soil acidity.

Step 1: Understand the Effect of Fertilizers

Different fertilizers have varying effects on soil pH. Fertilizers can be categorized based on whether they increase acidity (lower pH) or alkalinity (raise pH) of the soil. Ammonium-based fertilizers are known to increase the acidity of soil.

Step 2: Analyze Each Fertilizer's Composition

Break down the chemical composition of the options provided: - (a) Urea: CO(NH2)2, primarily used as a nitrogen source, often results in a neutral or slightly acidic effect. - (b) Super phosphate of lime: Ca(H2PO4)2, primarily a phosphorus source, typically has little effect on soil pH. - (c) Ammonium sulphate: (NH4)2SO4, contains ammonium ions which release hydrogen ions into the soil, increasing acidity. - (d) Potassium nitrate: KNO3, primarily a potassium source, usually has a neutral effect on soil pH.

Step 3: Determine the Acidifying Fertilizer

Identify which fertilizer among the options is known to increase soil acidity. Given the analysis, ammonium sulphate ((NH4)2SO4) releases hydrogen ions into the soil, thus making it more acidic. Therefore, ammonium sulphate is the fertilizer that increases soil acidity.

Key Concepts

Fertilizer Chemistry

Fertilizer chemistry is a fascinating area that delves into how fertilizers are composed and how these compositions affect the soil and plant growth. Different fertilizers contain varying nutrient compositions aimed at enhancing plant productivity. Some fertilizers are primarily nitrogen-based, while others might be rich in phosphorus or potassium.

• Nitrogen-based fertilizers like ammonium nitrate and urea are widely used to enhance leaf growth and overall plant vigor.
• Phosphorus fertilizers such as super phosphate help in root development and flowering.
• Potassium-based fertilizers like potassium nitrate improve the plant's resistance to diseases.

Understanding these components helps farmers and gardeners choose the right fertilizer based on plant needs and soil conditions.

Soil pH

Soil pH is a measure of the acidity or alkalinity of soil, which greatly affects nutrient availability and microbial activity. It is measured on a scale from 0 to 14, where 7 is neutral. Soils with a pH below 7 are considered acidic, while those above 7 are alkaline.

• An acidic soil can hinder the availability of essential nutrients like calcium and magnesium.
• An alkaline soil might limit access to micronutrients such as iron and zinc.
• Most plants prefer a slightly acidic to neutral pH, usually between 6 and 7.

Adjusting soil pH can be crucial to ensuring that plants receive the nutrients they need to thrive.

Ammonium Sulphate

Ammonium sulphate is a commonly used inorganic soil additive due to its dual benefits. It not only supplies nitrogen, an essential nutrient for plant growth, but also affects soil pH.

• Chemically, ammonium sulphate is composed of ammonium ions (NH4+) and sulfate ions (SO4^2-).
• The decomposition of ammonium ions in the soil releases hydrogen ions (H+), thus contributing to increased soil acidity.
• Because of this property, it is often used in alkaline soils where a decrease in pH is desired.

Understanding its chemical impact helps farmers manage soil pH effectively to maximize crop yield.

Agricultural Chemistry

Agricultural chemistry focuses on the chemical processes and compounds that occur in agriculture, particularly concerning plant nutrients and soil health. It plays a crucial role in understanding and optimizing soil fertility, crop protection, and environmental sustainability.

• It encompasses the study of macro and micronutrients essential for plant growth, including nitrogen, phosphorus, and potassium.
• Researchers in this field develop safer and more effective fertilizers and pesticides to boost agricultural productivity.
• It also addresses issues like soil degradation and remediation measures to preserve soil health over time.

Knowledge of agricultural chemistry is invaluable for farmers and agronomists aiming to sustainably increase crop yields while protecting the environment.