Long-term conservation agriculture to enhance soil properties and quality in rice–wheat cropping system – Nature

 

Report on the Long-Term Impact of Conservation Agriculture on Soil Quality and Productivity in the Rice-Wheat Cropping System

Executive Summary

This report details an on-farm study conducted in the northwestern Indo-Gangetic plains of India to assess the temporal effects of Conservation Agriculture (CA) on soil quality and its alignment with the Sustainable Development Goals (SDGs). The study compared conventional tillage (CT) with CA practices adopted for 2, 4, 8, and 12 years. Results indicate that long-term CA (≥8 years) is crucial for significantly improving soil physical, chemical, and biological properties, thereby restoring soil health and combating land degradation (SDG 15: Life on Land). These improvements led to a higher Soil Quality Index (SQI), which showed a strong positive correlation with crop productivity, directly supporting the goal of sustainable food production (SDG 2: Zero Hunger). The enhancement of soil organic carbon stocks under long-term CA also contributes to climate change mitigation (SDG 13: Climate Action). The findings advocate for the widespread, long-term adoption of CA as a key strategy for building climate-resilient, sustainable agricultural systems that support multiple SDGs.

1.0 Introduction: Aligning Agriculture with Sustainable Development Goals

The rice-wheat cropping system (RWS) of the Indo-Gangetic plains is fundamental to regional food security but faces sustainability challenges from conventional tillage-intensive practices. These practices lead to soil degradation, yield stagnation, and environmental pollution, undermining progress towards several Sustainable Development Goals.

1.1 The Challenge: Unsustainable RWS and Land Degradation (SDG 15)

Conventional agricultural practices in the RWS have resulted in significant environmental and productivity issues:

• Soil Degradation: Frequent tillage disrupts soil aggregates and accelerates the depletion of soil organic carbon (SOC), contributing to land degradation, a direct challenge to SDG 15 (Life on Land).
• Environmental Pollution: The common practice of burning crop residue degrades soil health and contributes to air pollution, impacting SDG 13 (Climate Action) and SDG 11 (Sustainable Cities and Communities).
• Yield Stagnation: The combination of degraded soils and inefficient residue management leads to stagnating crop yields, threatening food security and the objectives of SDG 2 (Zero Hunger).

1.2 The Solution: Conservation Agriculture as a Pathway to Sustainability

Conservation Agriculture (CA), based on principles of minimal soil disturbance, permanent soil cover, and crop diversification, emerges as a promising solution. This study investigates the time required for CA to manifest significant improvements in soil quality, thereby contributing to a more sustainable and productive agricultural model. The research hypothesizes that long-term CA adoption enhances soil properties and overall soil quality, fostering a system that is productive, resilient, and aligned with global sustainability targets.

2.0 Study Methodology

2.1 Site and Scenarios

The on-farm study was conducted in the Nilokheri block of Haryana, India, a region representative of the northwestern Indo-Gangetic plains. Soil samples were collected from fields under a continuous rice-wheat system with different management histories:

1. Conventional Tillage (CT): The control scenario with intensive tillage.
2. CA2: Conservation Agriculture practiced for 2 years.
3. CA4: Conservation Agriculture practiced for 4 years.
4. CA8: Conservation Agriculture practiced for 8 years.
5. CA12: Conservation Agriculture practiced for 12 years.

2.2 Soil Analysis and Quality Indexing

Soil samples were collected from 0-5 cm and 5-15 cm depths and analyzed for 22 different physical, chemical, and biological parameters. A comprehensive Soil Quality Index (SQI) was developed using Principal Component Analysis (PCA) to provide an integrated measure of soil health. This SQI was then validated against system productivity, measured as Rice Equivalent Yield (REY) and Wheat Yield (WY), to link soil health improvements directly to agricultural output, a key target of SDG 2.

3.0 Key Findings: Temporal Impacts of Conservation Agriculture on Soil Quality

The study revealed that the duration of CA practice is a critical factor, with significant improvements becoming evident primarily after eight years of adoption. Short-term CA (2-4 years) showed limited impact compared to conventional tillage.

3.1 Improvements in Soil Physical Properties (SDG 15)

Long-term CA (≥8 years) significantly improved the physical structure of the soil, a crucial step in reversing land degradation as targeted by SDG 15.

• Bulk Density (BD): Scenarios CA8 and CA12 showed 9.8% to 11.3% lower bulk density compared to CT, indicating reduced soil compaction.
• Water Dynamics: Mean Weight Diameter (MWD), Saturated Hydraulic Conductivity (Ks), and Water Holding Capacity (WHC) were significantly higher in CA8 and CA12, improving water infiltration and retention.

3.2 Enhancement of Soil Biological Health (SDG 15)

Soil biodiversity and biological activity, essential components of a healthy ecosystem under SDG 15, were markedly enhanced with long-term CA.

• Microbial Biomass Carbon (MBC): Increased by up to 42.7% in CA12 compared to CT in the surface soil.
• Enzyme Activity: Dehydrogenase (DHA) and β-glucosidase (GLUA) activities, key indicators of microbial function, were significantly higher in CA8 and CA12.
• Mycorrhizal Fungi: Glomalin content and mycorrhizal spore counts were significantly higher under long-term CA, indicating a healthier soil food web.

3.3 Positive Shifts in Soil Chemical Composition and Nutrient Availability (SDG 2)

Long-term CA improved soil fertility, which is vital for achieving the sustainable agriculture and food security goals of SDG 2.

• Nutrient Levels: Available Nitrogen (N), Phosphorus (P), Potassium (K), and Sulfur (S) were significantly higher in CA8 and CA12 scenarios.
• Micronutrients: Available levels of Iron (Fe), Manganese (Mn), Zinc (Zn), and Boron (B) were also enhanced under long-term CA.
• pH and EC: No significant changes were observed in soil pH or Electrical Conductivity (EC).

3.4 Soil Organic Carbon Sequestration: A Climate Action (SDG 13)

The study highlights CA’s role in climate change mitigation (SDG 13) through carbon sequestration.

• Soil Organic Carbon (SOC): SOC content increased by 39-59% in the topsoil under CA8 and CA12 compared to CT.
• SOC Stock: The CA12 scenario had 42.4% and 77.5% higher SOC stock over CT at 0-5 cm and 5-15 cm depths, respectively, demonstrating CA’s potential to turn agricultural soils into a carbon sink.

4.0 Assessing Overall Soil Health: The Soil Quality Index (SQI)

4.1 Key Indicators of Soil Quality

PCA identified the most sensitive indicators for assessing soil quality in this system. These indicators serve as vital metrics for monitoring progress towards sustainable land management (SDG 15.3).

• For 0-5 cm depth: β-glucosidase activity, Saturated Hydraulic Conductivity (Ks), Water Holding Capacity (WHC), available Sulfur (S), and available Copper (Cu).
• For 5-15 cm depth: Available Iron (Fe), Water Holding Capacity (WHC), available Copper (Cu), and Dehydrogenase activity (DHA).

4.2 SQI Results and Link to Productivity (SDG 2)

The integrated SQI confirmed the benefits of long-term CA and its direct link to agricultural productivity.

• SQI Trend: The highest SQI was observed in CA12, followed by CA8, CA4, CA2, and the lowest in CT at both soil depths. This demonstrates a clear dose-response relationship between the duration of CA and overall soil health.
• Productivity Correlation: A strong positive regression was found between the SQI and both Rice Equivalent Yield (R²=0.91-0.93) and Wheat Yield (R²=0.86-0.91). This powerful correlation validates that improving soil quality through CA is an effective strategy for enhancing crop yields and achieving the food security targets of SDG 2.

5.0 Conclusion and Recommendations for Achieving SDGs

5.1 Key Conclusions

1. Long-term commitment to Conservation Agriculture (≥8 years) is essential to significantly restore soil health, combat land degradation (SDG 15), and enhance soil organic carbon for climate action (SDG 13).
2. The Soil Quality Index (SQI) is a robust tool for holistically assessing soil health and serves as a reliable predictor of crop productivity, providing a tangible link between sustainable practices and food security (SDG 2).
3. Adopting CA for over eight years is a viable strategy to improve nutrient availability, enhance system productivity, and build climate-resilient cropping systems in the Indo-Gangetic plains.

5.2 Recommendations for Policy and Practice

To accelerate the achievement of the SDGs through agriculture, the following actions are recommended:

• Promote Long-Term Adoption: Policymakers and extension agencies should design programs that incentivize and support farmers to adopt CA practices for extended durations (8+ years) to realize the full spectrum of environmental and economic benefits.
• Utilize SQI for Monitoring: The SQI framework and its key indicators should be integrated into regional soil health monitoring programs to track progress towards land degradation neutrality (SDG 15.3) and guide adaptive management.
• Scale Up CA Practices: Widespread adoption of long-term CA-based rice-wheat rotation should be promoted as a cornerstone of sustainable and climate-smart agriculture in the region, contributing directly to national commitments under the Paris Agreement and the 2030 Agenda for Sustainable Development.

Analysis of Sustainable Development Goals in the Article

SDGs Addressed in the Article

1. SDG 2: Zero Hunger

   The article directly addresses SDG 2 by focusing on enhancing agricultural productivity and ensuring the sustainability of food production systems. The study evaluates Conservation Agriculture (CA) as a method to overcome the “yield stagnation and unsustainability” of the conventional rice-wheat cropping system (RWS), which is “crucial for ensuring food security.” The research aims to find ways to “boost agricultural productivity under CA, thereby fostering sustainable farming.”

2. SDG 15: Life on Land

   This goal is central to the article, which investigates methods to combat land degradation. The introduction highlights that conventional tillage practices “greatly accentuate soil erosion” and “degrade soil health.” The primary objective of the study is to assess how CA can “restore soil health and sustain productivity.” The research measures numerous soil parameters to quantify the reversal of degradation and the improvement of soil quality, which is fundamental to protecting terrestrial ecosystems.

3. SDG 13: Climate Action

   The article connects sustainable agricultural practices to climate resilience. It explicitly states that improvements in soil quality through CA are “vital for building climate-resilient cropping.” Furthermore, the study quantifies the increase in Soil Organic Carbon (SOC) stock, a key mechanism for carbon sequestration, which is a direct contribution to climate change mitigation. The challenges posed by conventional agriculture, such as residue burning, are also linked to environmental pollution, which has climate implications.

4. SDG 12: Responsible Consumption and Production

   The study promotes a shift from unsustainable production patterns (conventional tillage) to sustainable ones (Conservation Agriculture). Conventional practices are described as leading to “environmental pollution” through residue burning. CA, as defined by the FAO and studied in the article, promotes “minimum soil disturbance, continuous soil cover by crop residues, and crop diversification,” which represents a more sustainable management and efficient use of natural resources like soil and water, aligning with the principles of responsible production.

Specific Targets Identified

Targets Under Each SDG

1. SDG 2: Zero Hunger

   • Target 2.4: “By 2030, ensure sustainable food production systems and implement resilient agricultural practices that increase productivity and production, that help maintain ecosystems, that strengthen capacity for adaptation to climate change… and that progressively improve land and soil quality.”
   • Explanation: The entire article is an evaluation of Conservation Agriculture (CA) as a resilient and sustainable practice. It directly measures improvements in “soil quality,” “agricultural productivity” (rice and wheat yield), and the maintenance of the RWS ecosystem. The finding that “adopting CA for more than 8 years could help restore soil health and sustain productivity” is a direct contribution to this target.

2. SDG 15: Life on Land

   • Target 15.3: “By 2030, combat desertification, restore degraded land and soil, including land affected by desertification, drought and floods, and strive to achieve a land degradation-neutral world.”
   • Explanation: The study’s core focus is on reversing soil degradation. It quantifies how conventional tillage (CT) leads to soil health decline and how long-term CA can “restore soil health.” The detailed analysis of 22 different soil parameters, including physical, chemical, and biological properties, serves as a framework for monitoring and achieving land degradation neutrality.

3. SDG 13: Climate Action

   • Target 13.1: “Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.”
   • Explanation: The article explicitly mentions that the improvements from CA are “vital for building climate-resilient cropping.” By enhancing soil properties like water holding capacity and improving overall soil health, CA strengthens the agricultural system’s ability to withstand climate-related stresses such as erratic rainfall or drought, thus increasing its adaptive capacity.

4. SDG 12: Responsible Consumption and Production

   • Target 12.2: “By 2030, achieve the sustainable management and efficient use of natural resources.”
   • Explanation: The article contrasts the resource-degrading conventional tillage system with Conservation Agriculture, which is presented as a method for the sustainable management of soil. CA practices like minimum tillage and residue retention are shown to improve soil structure, water holding capacity, and nutrient availability, signifying a more efficient use of soil and water resources.

Indicators for Measuring Progress

Mentioned or Implied Indicators

1. Indicators for Agricultural Productivity and Soil Quality (Targets 2.4 & 15.3)

   • Crop Yield: The article uses “rice equivalent yield (REY),” “wheat yield (WY),” and “rice yield (RY)” as direct measures of agricultural productivity. It finds a “strong positive relationship” between the Soil Quality Index and both REY and WY.
   • Soil Quality Index (SQI): A composite index developed from 22 soil parameters to provide a single, comprehensive measure of soil health. The study shows that SQI increases with the duration of CA, with “the highest SQI… observed in CA12.”
   • Soil Organic Carbon (SOC) Stock: Explicitly calculated and presented as a key outcome. The article reports that the “CA12 scenario had 42.37 and 77.5% higher SOC stock over CT at topsoil (0–5 cm) and lower depth (5–15 cm), respectively.” This is a primary indicator for Target 15.3.
   • Soil Physical Properties:
     • Bulk Density (BD): Used to measure soil compaction. Lower BD indicates better soil health. “CA12 exhibited 11.1 and 9.8% lower BD… compared to CT.”
     • Water Holding Capacity (WHC) & Saturated Hydraulic Conductivity (Ks): Used to measure soil water dynamics. Higher values are desirable. “WHC in CA12 and CA8 treatments was 22.4 and 17.2%… higher… compared to CT fields at 0–5 cm soil depth.”
   • Soil Biological Properties:
     • Microbial Biomass Carbon (MBC): An indicator of microbial life in the soil. “The maximum MBC was recorded in the CA fields cultivated for 12 years, which is 42.7 and 33% higher than the conventionally tilled scenario.”
     • Enzyme Activities (Dehydrogenase – DHA, β-glucosidase – GLUA): Key indicators of microbial activity and nutrient cycling. “Twelve years after the conversion of CT fields to CA resulted in 34% higher DHA compared to the former.”
   • Soil Chemical Properties (Nutrient Availability): The study measures available macronutrients (N, P, K, S) and micronutrients (Fe, Mn, Zn, Cu, B) to assess soil fertility. For example, “after eight years of CA, Av. N was 31.7% higher in the topsoil… compared to CT.”

2. Indicator for Sustainable Practices (Target 12.2)

   • Adoption of Conservation Agriculture (CA): The duration of CA practice (2, 4, 8, and 12 years) is the primary independent variable in the study, serving as a direct indicator of the implementation of sustainable agricultural management.

Summary Table of Findings

SDGs	Targets	Indicators Identified in the Article
SDG 2: Zero Hunger	Target 2.4: Ensure sustainable food production systems and implement resilient agricultural practices to improve land and soil quality.	Agricultural Productivity (Rice Equivalent Yield – REY, Wheat Yield – WY) Soil Quality Index (SQI) Availability of soil nutrients (N, P, K, S, Fe, Mn, Zn, B)
SDG 15: Life on Land	Target 15.3: Combat desertification, restore degraded land and soil.	Soil Organic Carbon (SOC) content and stock Soil physical properties (Bulk Density, Mean Weight Diameter, Water Holding Capacity, Saturated Hydraulic Conductivity) Soil biological properties (Microbial Biomass Carbon, Dehydrogenase activity, β-glucosidase activity) Soil Quality Index (SQI)
SDG 13: Climate Action	Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards.	Qualitative assessment of “climate-resilient cropping” Improvement in soil’s Water Holding Capacity (WHC) Increase in Soil Organic Carbon (SOC) stock (mitigation co-benefit)
SDG 12: Responsible Consumption and Production	Target 12.2: Achieve the sustainable management and efficient use of natural resources.	Adoption and duration of Conservation Agriculture (CA) practices (minimum tillage, crop residue retention) Reduction in soil degradation indicators (e.g., improved bulk density)

Source: nature.com