IS S N 1 0 2 0 -4 5 5 5 Soil Organic Carbon Accumulation and Greenhouse Gas Emission Reductions from Conservation Agriculture: A literature review 16 Integrated Crop Management Vol. 16 –2012 S o il O r g a n ic C a r b o n A c c u m SSooiill oorrggaanniicc mmaatttteerr ppllaayyss aa ccrruucciiaall rroollee iinn mmaaiinnttaaiinniinngg ssooiill hheeaalltthh u SSooiill OOrrggaanniicc CCaarrbboonn AAccccuummuullaattiioonn aanndd la aanndd iittss pprroodduuccttiivviittyy ppootteennttiiaall.. HHoowweevveerr,, mmoosstt ooff tthhee wwoorrlldd’’ss tio aaggrriiccuullttuurraall ssooiillss hhaavvee bbeeccoommee ddeepplleetteedd iinn oorrggaanniicc mmaatttteerr n a GGrreeeennhhoouussee GGaass EEmmiissssiioonn RReedduuccttiioonnss n ccoommppaarreedd wwiitthh tthheeiirr ssttaattee uunnddeerr nnaattuurraall vveeggeettaattiioonn.. TThhiiss iiss d G bbeeccaauussee tthhee ddoommiinnaanntt ffoorrmm ooff aaggrriiccuullttuurree iiss bbaasseedd oonn ttiillllaaggee,, re ffrroomm CCoonnsseerrvvaattiioonn AAggrriiccuullttuurree:: e wwhhiicchh aacccceelleerraatteess tthhee ddeeccoommppoossiittiioonn ooff ssooiill oorrggaanniicc mmaatttteerr.. nh o TTiillllaaggee--bbaasseedd pprroodduuccttiioonn ssyysstteemmss sshhoouulldd tthheerreeffoorree bbee ttrraannssffoorrmmeedd u s e ssoo tthhaatt tthhee ffuuttuurree pprroodduuccttiioonn iinntteennssiifificcaattiioonn ccaann bbee aacchhiieevveedd G a AA lliitteerraattuurree rreevviieeww ssuussttaaiinnaabbllyy.. CCoonnsseerrvvaattiioonn AAggrriiccuullttuurree,, aa ssyysstteemm aavvooiiddiinngg oorr s E m mmiinniimmiizziinngg ssooiill ddiissttuurrbbaannccee,, ccoommbbiinneedd wwiitthh ssooiill ccoovveerr aanndd ccrroopp is s ddiivveerrssiifificcaattiioonn,, iiss ccoonnssiiddeerreedd ttoo bbee ssuucchh ssuussttaaiinnaabbllee pprroodduuccttiioonn io n ssyysstteemm.. HHoowweevveerr,, tthheerree aappppeeaarrss ttoo bbee cceerrttaaiinn ddeeggrreeee ooff R e d uunncceerrttaaiinnttyy aabboouutt tthhee rroollee ooff CCoonnsseerrvvaattiioonn AAggrriiccuullttuurree iinn ccaarrbboonn u c t sseeqquueessttrraattiioonn aanndd iinn rreedduucciinngg ggrreeeenn hhoouussee ggaass eemmiissssiioonnss.. TThhiiss io n ppuubblliiccaattiioonn pprreesseennttss aa mmeettaa aannaallyyssiiss ooff gglloobbaall sscciieennttiifificc lliitteerraattuurree s fr o wwiitthh tthhee aaiimm ttoo ddeevveelloopp aa cclleeaarr uunnddeerrssttaannddiinngg ooff tthhee iimmppaaccttss aanndd m C bbeenneefifittss ooff ttrraaddiittiioonnaall ttiillllaaggee aaggrriiccuullttuurree aanndd CCoonnsseerrvvaattiioonn o n AAggrriiccuullttuurree wwiitthh rreessppeecctt ttoo tthheeiirr eeffffeeccttss oonn ssooiill ccaarrbboonn ppoooollss.. TThhee se r v ssttuuddyy aatttteemmppttss ttoo rreedduuccee tthhee eexxiissttiinngg uunncceerrttaaiinnttyy aabboouutt tthhee a t iimmppaacctt ooff ssooiill mmaannaaggeemmeenntt pprraaccttiicceess oonn ssooiill ccaarrbboonn aanndd iiss ion A aaddddrreessssiinngg sscciieennttiissttss aass wweellll aass ppoolliiccyy mmaakkeerrss ttoo ffaacciilliittaattee ddeecciissiioonn g r mmaakkiinngg rreeggaarrddiinngg ffuuttuurree ffaarrmmiinngg mmooddeellss.. icu lt u r e : A lit e r a t u r e r ISBN978-92-5-107187-8 ISSN 1020-4555 ev ie w 9 7 8 9 2 5 1 0 7 1 8 7 8 F I2672E/1/03.12 A O Integrated Crop Management Vol.16-2012 Soil Organic Carbon Accumulation and Greenhouse Gas Emission Reductions from Conservation Agriculture: A literature review Sandra Corsi1, 3, Theodor Friedrich1, Amir Kassam1, 2, Michele Pisante3 and João de Moraes Sà4 1 Plant Production and Protection Division (AGP), FAO, Rome, Italy 2 School of Agriculture, Policy and Development, University of Reading, United Kingdom 3 Agronomy and Crop Sciences Research and Education Centre, University of Teramo, Italy 4 Universidade Estadual de Ponta Grossa-PR, Brazil PLANT PRODUCTION AND PROTECTION DIVISION FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Rome, 2012 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 (FAO) 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. The mention of specific companies or products of manufacturers, whether or not these have been patented, does not imply that these have been endorsed or recommended by FAO in preference to others of a similar nature that are not mentioned. The views expressed in this information product are those of the author(s) and do not necessarily reflect the views of FAO. ISBN 978-92-5-107187-8 All rights reserved. FAO encourages reproduction and dissemination of material in this information product. Non-commercial uses will be authorized free of charge, upon request. Reproduction for resale or other commercial purposes, including educational purposes, may incur fees. Applications for permission to reproduce or disseminate FAO copyright materials, and all other queries on rights and licences, should be addressed by e-mail to [email protected] or to the Chief, Publishing Policy and Support Branch, Office of Knowledge Exchange, Research and Extension, FAO, Viale delle Terme di Caracalla, 00153 Rome, Italy. © FAO 2012 CONTENTS CONTENTS v Foreword vi Acknowledgements vii Abbreviations ix Summary CHAPTER 1 1 Introduction CHAPTER 2 5 Definitions 5 The pathway of carbon from crop residues into soil organic matter and soil organic carbon 8 Conservation Agriculture for carbon storage in cropland CHAPTER 3 13 Evidence that CA promotes soil carbon accumulation 13 Where CA principles and methods are not followed 13 Soil disturbance 15 Monocropping 16 Crop rotations and cover crops that do not allow a positive N balance 17 Crop residues removal and mixing 19 Rhizodeposits and SOC accumulation in deeper soil layers 20 Variables influencing soil carbon accumulation: analyzing global data 23 Subhumid and humid tropical and subtropical zones 24 Tropical and subtropical semi-arid zones 26 Temperate zones 27 Influence of soil and crop management systems on SOC - lessons learnt CHAPTER 4 31 Is the carbon budget for CA systems higher than for TA systems? 31 Mechanical equipment 32 Fertilization 34 GHG dynamics 34 Methane emissions 35 Nitrous oxide emissions Vol. 16–2012 iii SOILORGANICCARBONACCUMULATIONANDGREENHOUSEGASEMISSIONREDUCTIONSFROM CONSERVATION AGRICULTURE CHAPTER 5 39 Concluding comments 43 References 65 Annexes 67 Glossary iv Integrated Crop Management FOREWORD Soil organic matter plays a crucial role in maintaining soil health and its productivity potential. However, most of the world’s agricultural soils have become depleted in organic matter and therefore soil health over the years, compared with their state under natural vegetation. This is because the dominant form of agriculture is based on tillage, which accelerates the decomposition of soil organic matter. At the same time, there has been a tendency for tillage agriculture to remove much or all of the crop residues, thus leaving the soil starved of substrate for soil organisms to maintain soil structure and exposed to soil erosion. This degradation process decreases soil’s ability to hold water and nutrients, reduces rainfall infiltration and leads to increased soil compaction and loss of soil biodiversity. Such agricultural soils are not able to offer the best factor productivities for production inputs such as nutrient, water and labour, and are not able to harness environmental services such as clean water, carbon sequestration and control of erosion and pests. Thus, tillage-based production systems are considered generally unsustainable and it is important that our farming systems are transformed so the future production intensification can be achieved sustainably. In addition to sustainable production intensification and enhancing factor productivity, there is a need to transform farming practices to sequester carbon so that climate change mitigation becomes an inherent property of future farming systems. Conservation Agriculture, a system avoiding or minimizing soil disturbance, combined with soil cover and crop diversification, is considered to be a sustainable production system that can also sequester carbon unlike tillage agriculture. However, there appears to be certain degree of uncertainty about the role of Conservation Agriculture in carbon sequestration and its role in reducing green house gas emissions. This publication presents a meta analysis of global scientific literature with the aim to develop a clear understanding of the impacts and benefits of the two most common types of agriculture, traditional tillage agriculture and Conservation Agriculture with respect to their effects on soil carbon pools. The study conducted by the Plant production and Protection Division in collaboration with experts from several universities attempts to reduce the existing uncertainty about the impact of soil management practices on soil carbon pools and on carbon budget. Shivaji Pandey Director Plant Production and Protection Division Vol. 16–2012 v SOILORGANICCARBONACCUMULATIONANDGREENHOUSEGASEMISSIONREDUCTIONSFROM CONSERVATION AGRICULTURE ACKNOWLEDGEMENTS This study is the product of cooperative work by the working group on Conservation Agriculture (CA) of the Plant Production and Protection Division (AGP) of the Food and Agriculture Organization (FAO) with universities of Reading (UK), Teramo (Italy) and Ponta Grossa (Brazil). It has benefited from the support and inputs from a number of individuals who reviewed the draft. The internal reviewers from FAO were Christian Nolte, Lawrence Narteh, Gualbert Gbehounou and Cornelis van Duijvendijk. The external reviewers were Richard Harwood (Michigan State University, USA), Tom Goddard (Alberta Agriculture and Rural Development, Canada), and Gottlieb Basch (University of Evora, Portugal). To them all we express our special thanks. Brian Sims edited the final draft and Magda Morales formatted the document for printing. We express our appreciation to them both. vi Integrated Crop Management ABBREVIATIONS AGP Plant Production and Protection Division of the Food and Agriculture Organization CA Conservation Agriculture CH Methane 4 CO Carbon dioxide 2 FAO Food and Agriculture Organisation of the United Nations GHG Atmospheric greenhouse gas IIASA International Institute for Applied Systems Analysis MLRA major land resource area MT Minimum tillage NO Nitrous oxide 2 NT No-till SOC Soil organic carbon SOM Soil organic matter TA Tillage agriculture Vol. 16–2012 vii SUMMARY This study aims at developing a clear understanding of the impacts and benefits of the two most common types of agriculture, traditional tillage agriculture (TA) and Conservation Agriculture (CA), a no-till system, with respect to their effects on soil carbon pools. It is based on a meta analysis of scientific literature, attempting to reduce the existing uncertainty about the impact of soil management practices on soil carbon pools. The results from literature review on carbon sequestration in TA are compared with CA, a broader agro-ecosystem management concept that requires compliance with three interrelated criteria, namely minimum or no mechanical soil disturbance, permanent organic soil cover, and diversified crop associations and rotations. The review shows that CA permits higher rates of carbon sequestration in the soil compared with TA. When no carbon sequestration or carbon loss is reported in agricultural systems, this is most frequently associated with any one or a combination of the following reasons: i) soil disturbance, ii) monocropping, iii) specific crop rotations, iv) poor management of crop residues, and v) soil sampling extended deeper than 30 cm. Most of the world’s agricultural soils have become depleted in organic matter and soil health over the years under TA, compared with their state under natural vegetation. This degradation process has proved to be reversible and the main ways to increase soil organic matter content and improve soil health seem to be: i) keeping the disturbance impact and interactions between mechanical implements and soil to an absolute minimum, ii) using effective crop rotations and associations, and iii) leaving crop residues as carbon source on the soil surface. The implementation of these practices can help restore a degraded agro-ecosystem to a sustainable and productive state. However, soil organic carbon (SOC) sequestration is generally non-linear over time and the effectiveness of conversion of a farming system from TA to CA depends on a number of variables: for example, soil carbon sink strength increases most rapidly soon after a carbon-enhancing change in land management has been implemented, and reduces with time as the stable SOC stock approaches a new equilibrium which in agricultural soils in Europe for example can take approximately 100 years after a carbon-enhancing land use change has been introduced. Even though some authors report significant increase in microbial activity soon after transition to CA, fuller advantages of CA in terms of soil health and its productive capacity can usually be observed only in the medium- to longer-term, when CA practices and soil biological processes become well established within the farming system. Vol. 16–2012 ix SOILORGANICCARBONACCUMULATIONANDGREENHOUSEGASEMISSIONREDUCTIONSFROM CONSERVATION AGRICULTURE The study discusses the effectiveness of using average rates of soil carbon content for estimating sequestration at the global level. In reality, there are different carbon pools in the soil undergoing transformation from the undecomposed form to decomposing unstable form to decomposed stable form. The carbon sequestration potential of any soil, for the carbon pool considered, depends on the vegetation it supports (which influences the amount and chemical composition of organic matter being added), soil moisture availability, soil mineralogical composition and texture, depth, porosity and temperature. Therefore, when addressing carbon sequestration, rates should always be referred to specific carbon pools, as each carbon category has highly different turnover rates. Another aspect of CA in relation to carbon budgets are the reduced power and energy requirements as a result of not tilling the soil. This translates into less fuel consumption, lower working time and slower depreciation rates of equipment per unit area per unit of output, all leading to emission reductions from the various farm operations as well as from the machinery manufacturing processes. In addition, crop residues left in the field return the carbon fixed in the crops by photosynthesis to the soil and the resulting improvement in soil health and fertility leads, over time, to reduced fertilizer use, and CO emissions. 2 Other relevant green house gas (GHG) emissions from agriculture, namely methane and nitrous oxides can also be reduced within a CA environment with some complementary practices. This paper concludes that terrestrial sequestration of carbon can efficiently be achieved by changing the management of agricultural lands from high soil disturbance practices to low disturbance and by adopting effective nitrogen management practices so that the nitrogen balance remains positive. CA allows agro-ecosystems to store more CO , emit less and all in all improve ecosystem 2 functioning and services, such as the control of rainfall runoff and soil erosion, carbon sequestration including below the plough layer and, when a mulch cover is adopted, increase in water infiltration. The combined environmental benefits of CA at the farm and landscape level can contribute to global environmental conservation and also provide a low-cost option to help offset emissions of the main GHGs. With CA fewer and/or smaller tractors can be used and fewer passes over the field are needed , which also result in lower fuel and repair costs. However, fuller productivity, economic and environmental advantages of CA can usually be seen only in the medium- to longer-term when CA practices and new soil conditions are well established. These important lessons learnt from around the world regarding the high potential for carbon sequestration with CA systems and the associated opportunity for carbon trading and reduction in GHGs emissions should be taken into consideration in any climate change mitigation strategy for the future. x Integrated Crop Management