Problem Soils and their Reclamation | Agriculture Optional Notes for UPSC PDF Download

Introduction

Problem soils are those with inherent unfavorable conditions that lower their productivity, such as high salt content and adverse soil pH levels. In India, the extent of salt-affected soils has significantly increased to cover 6.74 million hectares. Soil salinity stands as one of the major challenges constraining crop production in arid and semi-arid regions worldwide.

Types of problematic soil

Problem soils can be categorized into several types, including:

• Saline soil
• Sodic/alkaline soil
• Saline-sodic soil
• Acidic soils

Other problematic soils, such as acid sulfate soils and calcareous soils

Salt-Affected Soil

Salt-affected soil is a prevalent issue in India, primarily found in four major regions:

• Semi-arid Indo-Gangetic alluvial tract
• Arid tract of Rajasthan and Gujarat
• Arid and semi-arid tract of central and southern states
• Coastal alluvial soil

In India, saline soils cover approximately 2.96 million hectares, with Gujarat and Rajasthan being the primary states affected. Sodic soils encompass 3.78 million hectares, with Uttar Pradesh and Gujarat leading in prevalence.

Characteristics of Salt-Affected Soil

• Saline soils contain neutral soluble salts of chlorides and sulfates of sodium, calcium, and magnesium. These soils typically have an electrical conductivity of the saturated extract exceeding 4 dS m-1, an exchangeable sodium percentage (ESP) below 15, and a pH level below 8.5. Their physical condition is relatively good, allowing water to pass through them, and they often exhibit a white crust of salts on the surface.
• In contrast, alkali or sodic soils contain most of the sodium in exchangeable form. Their electrical conductivity of saturated extract is typically lower than 4 dS m-1, ESP exceeds 15, and pH is above 8.5. These soils usually have a poor physical condition, sometimes resulting in slick spots when plowed when wet.
• Saline-alkali soils combine characteristics of both saline and sodic soils. They have high electrical conductivity (above 4 dS m-1), ESP exceeding 15, and a pH around 8.5. These transitional soils can transform into saline or sodic soils.

Comparison of the Characteristics of Salt-Affected Soils

A comparison of the characteristics of salt-affected soils is presented in the table below:

Reclamation of Saline Soils

Several methods can be employed to reclaim saline soils:

• Cultural Practices
  • Scraping
  • Flushing
  • Leaching
  • Improving irrigation
  • Land leveling
  • Subsoiling
  • Sanding
  • Safe disposal of saline water
• Tolerant and Sensitive Crops
  • Crops such as sorghum, wheat, triticale, oats, barley, and some vegetable crops exhibit high tolerance to soil salinity.
• Biological Reclamation
  • Decomposing organic matter in the soil liberates carbon dioxide and organic acids, which help dissolve insoluble calcium salts.
  • Green manuring, crop residues, and afforestation are among the biological methods for reclamation.
• Chemical Method
  • Gypsum and sulfur are commonly used to amend saline soils.
  • Gypsum reacts with sodium carbonate to replace sodium with calcium, aiding in reclamation.
• Irrigation Water Management
  • Proper irrigation frequency and methods are crucial for controlling salt levels in the soil.

Reclaiming of Sodic Soils

Reclaiming sodic soils involves the removal of exchangeable sodium by replacing it with more favorable calcium ions in the root zone. This can be achieved through chemical, cultural, biological, and irrigation water management methods.

• Chemical Method: Chemical amendments like gypsum and calcium chloride can be used to replace exchangeable sodium with calcium.
• Cultural Method: Deep ploughing, subsoiling, sanding, land leveling, and other cultural practices can help reclaim sodic soils.
• Biological Method: Applying bulky organic manure, green manure, crop residues, and crop rotation can contribute to sodic soil reclamation.
• Tolerant and Sensitive Crops: Choosing crops that are tolerant to excess exchangeable sodium is essential during the reclamation process.
• Irrigation Water Management: Leaching with high-quality water and the use of suitable irrigation methods further aid in displacing adsorbed sodium.

Reclaiming of Saline-Sodic Soils

Saline-sodic soils can be reclaimed by replacing exchangeable sodium with calcium, typically through the application of gypsum or sulfur. Proper leaching with low-sodium water is essential in the reclamation process.

Acidic Soils

Soils with a pH below 7 are termed acidic soils, often containing excessive amounts of dissolved ions of aluminum, iron, manganese, and copper. These soils are deficient in calcium and magnesium. Acid sulfate soils, which have a pH below 3.5, can cause crop issues due to aluminum toxicity and nutrient deficiencies.

Distribution of Acid Soils in India

• Total area with acid soils: 92 million hectares
• Major affected states: Madhya Pradesh (1st), Maharashtra (2nd)
• Acid soils constitute about 28% of the total geographical area, with 9.3% having a pH below 5.5 and 18.9% falling within the pH range of 5.5-6.5.

Formation of Acid Soils

Several factors contribute to the formation of acid soils, including parent materials, acid rain, acid-forming fertilizers, high rainfall areas, and highly weathered soils.

Reclaiming of Acid Soils

Reclaiming acid soils involves the following methods:

• Liming: The application of lime, including burnt lime, hydrated lime, basic slag, dolomite, and calcite, is recommended to improve base saturation and neutralize harmful ions.
• Choice of Crops: Selecting crops like rice, millets, oats, groundnut, tea, and potatoes, which are tolerant to soil acidity, can ensure reasonable returns.
• Soil Fertility Management
  • Proper nitrogen fertilizer management, including split applications, can reduce leaching losses.
  • The use of water-soluble sources like SSP, TSP, and DAP is preferred over murate of potash.
• Problems Associated with Over Liming: Over-liming can lead to issues such as deficiencies in iron, copper, manganese, zinc, reduced phosphorus availability, and increased disease incidence, such as Scab in root crops. It can also cause boron deficiency and root tip swelling due to high OH- ion concentrations.

Other Problematic Soils - Acid Sulphate Soils (Kari Soils)

These soils are primarily found in regions like Kottayam and Alleppey in Kerala, the coastal areas of Odisha, and the Sundarbans in West Bengal. Acid sulfate soils are rich in pyrites (FeS2), which, upon oxidation, form sulfuric acid, resulting in a pH below 3.5. They typically occur in humid regions with frequent tides.

Management of Acid Sulphate Soils

Managing acid sulfate soils involves addressing the acidic conditions and preventing the formation of sulfuric acid. This can be achieved through proper drainage and soil amendments.

In conclusion, understanding and effectively managing problem soils is crucial for sustainable agriculture and ensuring food security in regions affected by these soil-related challenges. Utilizing appropriate reclamation methods and crop selection can significantly improve soil conditions and agricultural productivity in affected areas.