FAO SOILS BULLETIN 80

FAO SOILS BULLETIN 80

The importance
of soil organic matter
Key to drought-resistant soil
and sustained food production

by
Alexandra Bot
FAO Consultant

and

José Benites
FAO Land and Plant Nutrition
Management Service

   
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Rome, 2005
   
 

Table of Contents


Cover photographs:
Background: Honduras. FAO/18884/G. Bizzarri.
Inset: Honduras. FAO/18907/G. Bizzarri.

The designations employed and the presentation of material in this information product do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal or development status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

ISBN 92-5-105366-9
ISSN 0253-2050

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© FAO 2005


Contents

Acknowledgements

Preface

List of acronyms

1. Introduction

2. Organic matter decomposition and the soil food web

Soil organic matter
The soil food web
Decomposition process

Non-humic substances: significance and function
Compounds and function of humus

3. Natural factors influencing the amount of organic matter

Temperature
Soil moisture and water saturation
Soil texture
Topography
Salinity and acidity
Vegetation and biomass production

4. Practices that influence the amount of organic matter

Human interventions that influence soil organic matter

Practices that decrease soil organic matter

Decrease in biomass production

Replacement of perennial vegetation
Replacement of mixed vegetation with monoculture of crops and pastures
High harvest index
Use of bare fallow

Decrease in organic matter supply

Burning of natural vegetation and crop residues
Overgrazing
Removal of crop residues

Increased decomposition rates

Tillage practices
Drainage
Fertilizer and pesticide use

Practices that increase soil organic matter
Increased biomass production

Increased water availability for plants: water harvesting and irrigation
Balanced fertilization
Cover crops
Improved vegetative stands
Agroforestry and alley cropping
Reforestation and afforestation
Regeneration of natural vegetation

Increased organic matter supply

Protection from fire
Crop residue management
Utilizing forage by grazing rather than by harvesting
Integrated pest management
Applying animal manure or other carbon-rich wastes
Compost
Mulch or permanent soil cover

Decreased decomposition rates

Reduced or zero tillage

5. Creating drought-resistant soil

Effect of soil organic matter on soil properties
Inefficient use of rainwater
Increased soil moisture
Reduced soil erosion and improved water quality

6. Key factors in sustained food production

Increased plant productivity
Increased fertilizer efficiency
Reduced waterlogging
Increased yields
Reduced herbicide and pesticide use
Increased biodiversity
Resilience

7. The role of conservation agriculture in organic matter deposition and carbon sequestration

Principles of conservation agriculture
Organic matter deposition
Increased carbon sequestration

8. Conclusions

Bibliography

Annexes

Annex 1. Soil organisms
Annex 2. Effects of organic matter on soil properties

FAO technical papers

Back cover