Understanding Soil Organic Carbon Decline: Insights from ICAR Study

Declining Soil Organic Carbon in India: ICAR Study Highlights

A recent study by the Indian Council of Agricultural Research (ICAR) has revealed that unscientific fertilizer use and climate change are among the primary causes of declining Soil Organic Carbon (SOC) levels in India’s arable lands. Falling SOC levels pose a major threat to soil health, crop productivity, and the long-term sustainability of agriculture.

Understanding Soil Organic Carbon (SOC)

Soil Organic Matter (SOM) consists of organic residues at various decomposition stages and plays a critical role in maintaining soil health. The largest component of SOM is Soil Organic Carbon (SOC). SOC forms the biggest terrestrial carbon reservoir and is essential for the planet’s carbon cycle. It helps soils provide vital ecosystem services, making SOC a key scientific indicator of overall soil health.

Background of the ICAR Study

The study, initiated in 2017 and coordinated by the ICAR–Indian Institute of Soil Science (IISS), Bhopal, analyzed soil samples across 29 Indian states. It provides a comprehensive assessment of how SOC levels are changing across India’s agricultural landscapes and identifies major factors responsible for soil degradation.

Key Drivers of Soil Organic Carbon Decline

• Impact of Climate Change: Rising temperatures adversely affect SOC levels. While rainfall changes have minimal direct impact, increased heat accelerates decomposition and carbon loss. Reduced SOC further weakens soil health and increases heat reflection, intensifying the greenhouse effect.
• Correlation Between SOC and Micronutrients: A strong relationship exists between organic carbon and soil micronutrient levels. Low SOC is associated with high micronutrient deficiency, which reduces soil fertility and crop nutrition.
• Influence of Altitude: Organic carbon content increases with elevation. Higher-altitude soils tend to retain more carbon due to cooler temperatures and slower organic matter decomposition.
• Impact of Cropping Systems: Rice and pulse-based cropping systems show higher SOC levels. In contrast, wheat and coarse-grain systems exhibit lower SOC due to reduced biomass return and intensive tillage practices.
• Imbalanced Fertilizer Use: Unbalanced fertilizer use—particularly excessive application of urea and phosphorus—in regions like Punjab, Haryana, and Western Uttar Pradesh has led to rapid SOC depletion and soil health deterioration.

Other Impacts of Climate Change on Agriculture

• Changed Growing Seasons: Shifts in seasonal temperature and rainfall patterns alter crop calendars, disrupting traditional planting and harvesting cycles.
• Increased Pests and Diseases: Rising temperatures expand the geographical range of plant pathogens, exposing new areas to pests and leading to severe crop losses.
• Water Scarcity: Prolonged meteorological droughts, intensified by global warming, reduce water availability for irrigation and threaten agricultural productivity.

Recommendations for Soil Restoration

• Balanced Nutrient Management: Adopt balanced fertilizer application, sustainable cropping practices, and policy incentives to restore SOC and control land degradation.
• Promote Carbon Sequestration: Encourage organic carbon sequestration in soils that contain less than 0.25% carbon.
• Carbon Credit Incentives: Introduce carbon credit benefits for farmers contributing to soil carbon enhancement.
• Continuous Crop Cover: Promote continuous crop cover and large-scale plantation efforts to reduce soil erosion and improve organic content.
• Climate-Resilient Crop Management: Develop and adopt climate-resilient crop management systems to mitigate SOC loss and maintain soil productivity.
• Climate-Adaptive Varieties: Breed and promote crop varieties that can adapt to climate variability, combined with improved agronomic practices and pest management.

Frequently Asked Questions (FAQs)

Q1. What is Soil Organic Carbon (SOC)?
Answer: Soil Organic Carbon (SOC) is a crucial component of Soil Organic Matter (SOM) that plays a significant role in soil health and fertility. It is the largest terrestrial carbon reservoir and is vital for the carbon cycle and ecosystem services.

Q2. How does climate change affect SOC levels?
Answer: Climate change affects SOC levels primarily through rising temperatures, which accelerate decomposition and carbon loss. This leads to decreased soil health and productivity.

Q3. What are the impacts of imbalanced fertilizer use?
Answer: Imbalanced fertilizer use, particularly excessive application of urea and phosphorus, can lead to rapid SOC depletion and deterioration of soil health, especially in specific regions of India.

Q4. How can SOC levels be restored?
Answer: SOC levels can be restored through balanced nutrient management, promoting carbon sequestration, and adopting sustainable agricultural practices to enhance soil health and fertility.

Q5. What role do cropping systems play in SOC levels?
Answer: Different cropping systems impact SOC levels significantly. Rice and pulse-based systems generally promote higher SOC levels, while wheat and coarse-grain systems tend to reduce them due to lower biomass return.