Downloaded from rstb.royalsocietypublishing.org on August 29, 2012The role of conservation agriculture in sustainable agri...
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The Role of Conservation Agriculture in Sustainable Agriculture
The Role of Conservation Agriculture in Sustainable Agriculture
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The Role of Conservation Agriculture in Sustainable Agriculture

  1. 1. Downloaded from rstb.royalsocietypublishing.org on August 29, 2012The role of conservation agriculture in sustainable agriculturePeter R Hobbs, Ken Sayre and Raj GuptaPhil. Trans. R. Soc. B 2008 363, 543-555doi: 10.1098/rstb.2007.2169References This article cites 70 articles, 1 of which can be accessed free http://rstb.royalsocietypublishing.org/content/363/1491/543.full.html#ref-list-1 Article cited in: http://rstb.royalsocietypublishing.org/content/363/1491/543.full.html#related-urlsEmail alerting service Receive free email alerts when new articles cite this article - sign up in the box at the top right-hand corner of the article or click hereTo subscribe to Phil. Trans. R. Soc. B go to: http://rstb.royalsocietypublishing.org/subscriptions
  2. 2. Downloaded from rstb.royalsocietypublishing.org on August 29, 2012 Phil. Trans. R. Soc. B (2008) 363, 543–555 doi:10.1098/rstb.2007.2169 Published online 24 July 2007 The role of conservation agriculture in sustainable agriculture Peter R. Hobbs1,*, Ken Sayre2 and Raj Gupta3 1 Department of Crops and Soil Science, Cornell University, Ithaca, NY 14853, USA 2 CIMMYT Apdo, Postal 6-641, 06600 Mexico DF, Mexico 3 ICARDA-CAC office, P.O. Box 4564, Tashkent 700000, Uzbekistan The paper focuses on conservation agriculture (CA), defined as minimal soil disturbance (no-till, NT) and permanent soil cover (mulch) combined with rotations, as a more sustainable cultivation system for the future. Cultivation and tillage play an important role in agriculture. The benefits of tillage in agriculture are explored before introducing conservation tillage (CT), a practice that was borne out of the American dust bowl of the 1930s. The paper then describes the benefits of CA, a suggested improvement on CT, where NT, mulch and rotations significantly improve soil properties and other biotic factors. The paper concludes that CA is a more sustainable and environmentally friendly management system for cultivating crops. Case studies from the rice–wheat areas of the Indo-Gangetic Plains of South Asia and the irrigated maize–wheat systems of Northwest Mexico are used to describe how CA practices have been used in these two environments to raise production sustainably and profitably. Benefits in terms of greenhouse gas emissions and their effect on global warming are also discussed. The paper concludes that agriculture in the next decade will have to sustainably produce more food from less land through more efficient use of natural resources and with minimal impact on the environment in order to meet growing population demands. Promoting and adopting CA management systems can help meet this goal. Keywords: conservation agriculture; direct seeding; zero-tillage; rice–wheat systems; bed planting; mulching1. INTRODUCTION sustainable agricultural production. But first, theConservation agriculture (CA) defined (see FAO CA paper discusses some issues related to tillage.web site: http://www.fao.org/ag/ca/1a.html ) as minimalsoil disturbance (no-till, NT) and permanent soil cover(mulch) combined with rotations, is a recent agricul- 2. CULTIVATION TECHNIQUES OR TILLAGEtural management system that is gaining popularity in The history of tillage dates back many millennia whenmany parts of the world. Cultivation is defined by the humans changed from hunting and gathering to moreOxford English dictionary as ‘the tilling of land’, ‘the sedentary and settled agriculture mostly in the Tigris,raising of a crop by tillage’ or ‘to loosen or break up Euphrates, Nile, Yangste and Indus river valleys (Hillelsoil’. Other terms used in this dictionary include 1991). Reference to ploughing or tillage is found from‘improvement or increase in (soil) fertility’. All these 3000 BC in Mesopotamia (Hillel 1998). Lal (2001)definitions indicate that cultivation is synonymous with explained the historical development of agriculturetillage or ploughing. with tillage being a major component of management The other important definition that has been practices. With the advent of the industrial revolutiondebated and defined in many papers is the word in the nineteenth century, mechanical power and‘sustainable’. The Oxford English dictionary defines tractors became available to undertake tillagethis term as ‘capable of being borne or endured, operations; today, an array of equipment is availableupheld, defended, maintainable’. Something that is for tillage and agricultural production. The followingsustained is ‘kept up without intermission or flagging, summarizes the reasons for using tillage.maintained over a long period’. This is an importantconcept in today’s agriculture, since the human race (i) Tillage was used to soften the soil and prepare awill not want to compromise the ability of its future seedbed that allowed seed to be placed easily at aoffspring to produce their food needs by damaging the suitable depth into moist soil using seed drills ornatural resources used to feed the population today. manual equipment. This results in good This paper will introduce and promote CA as a uniform seed germination.modern agricultural practice that can enable farmers in (ii) Wherever crops grow, weeds also grow andmany parts of the world to achieve the goal of compete for light, water and nutrients. Every gram of resource used by the weed is one less gram for the crop. By tilling their fields, farmers* Author for correspondence (ph14@cornell.edu). were able to shift the advantage from the weed toOne contribution of 16 to a Theme Issue ‘Sustainable agriculture I’. the crop and allow the crop to grow without 543 This journal is q 2007 The Royal Society
  3. 3. Downloaded from rstb.royalsocietypublishing.org on August 29, 2012544 P. R. Hobbs et al. Role of CA in sustainable agriculture competition early in its growth cycle with invented a new name to describe the process’. The resulting higher yield. book goes on to list 14 different names for reduced (iii) Tillage helped release soil nutrients needed tillage along with rationales for using these names. for crop growth through mineralization and The book is also an excellent review of the oxidation after exposure of soil organic matter mechanization and equipment needs of no-tillage to air. technologies. Baker et al. (2002) defined CT as: (iv) Previous crop residues were incorporated along the collective umbrella term commonly given to with any soil amendments (fertilizers, organic or no-tillage, direct-drilling, minimum-tillage and/or inorganic) into the soil. Crop residues, ridge-tillage, to denote that the specific practice has a especially loose residues, create problems for conservation goal of some nature. Usually, the seeding equipment by raking and clogging. retention of 30% surface cover by residues charac- (v) Many soil amendments and their nutrients are terizes the lower limit of classification for conservation- more available to roots if they are incorporated tillage, but other conservation objectives for the into the soil; some nitrogenous fertilizers are practice include conservation of time, fuel, earth- also lost to the atmosphere if not incorporated. worms, soil water, soil structure and nutrients. Thus (vi) Tillage gave temporary relief from compaction residue levels alone do not adequately describe all using implements that could shatter below- conservation tillage practices. ground compaction layers formed in the soil. (Baker et al. 2002, p. 3) (vii) Tillage was determined to be a critical manage- ment practice for controlling soil-borne diseases This has led to confusion among the agricultural and some insects. scientists and, more importantly, the farming commu- There is no doubt that this list of tillage benefits was nity. To add to the confusion, the term ‘conservationbeneficial to the farmer, but at a cost to him and the agriculture’ has recently been introduced by the Foodenvironment, and the natural resource base on which and Agriculture Organization (see FAO web site), andfarming depended. The utility of ploughing was first others, and its goals defined by FAO as follows:questioned by a forward-looking agronomist in the Conservation agriculture (CA) aims to conserve,1930s, Edward H. Faulkner, in a manuscript called improve and make more efficient use of natural‘Ploughman’s Folly’ (Faulkner 1943). In a foreword to resources through integrated management of availablea book entitled ‘Ploughman’s folly and a second look’ soil, water and biological resources combined withby EH Faulkner, Paul Sears notes that: external inputs. It contributes to environmental conservation as well as to enhanced and sustained Faulkner’s genius was to question the very basis of agricultural production. It can also be referred to as agriculture itself—the plough. He began to see that the resource efficient or resource effective agriculture. curved moldboard of the modern plough, rather than (FAO) allowing organic matter to be worked into the soil by worms and other burrowing animals, instead buries this This obviously encompasses the ‘sustainable agri- valuable material under the subsoil where it remains cultural production’ need that all mankind obviously like a wad of undigested food from a heavy meal in the wishes to achieve. But this term is often not human stomach. distinguished from CT. The FAO mentions in its CA ( Faulkner 1987, p. x) website that: Conservation tillage is a set of practices that leave crop The tragic dust storm in the mid-western United residues on the surface which increases water infiltra-States in the 1930s was a wake-up call to how human tion and reduces erosion. It is a practice used ininterventions in soil management and ploughing led to conventional agriculture to reduce the effects of tillageunsustainable agricultural systems. In the 1930s, it was on soil erosion. However, it still depends on tillage asestimated that 91 Mha of land was degraded by severe the structure forming element in the soil. Never thesoil erosion (Utz et al. 1938); this area has been less, conservation tillage practices such as zero tillagedramatically reduced today. practices can be transition steps towards Conservation Agriculture.3. CONSERVATION TILLAGE AND CONSERVA- In other words, CT uses some of the principles ofTION AGRICULTURE CA but has more soil disturbance.Since the 1930s, during the following 75 years,members of the farming community have beenadvocating a move to reduced tillage systems that 4. CONSERVATION AGRICULTURE DEFINEDuse less fossil fuel, reduce run-off and erosion of soils The FAO has characterized CA as follows:and reverse the loss of soil organic matter. The first Conservation Agriculture maintains a permanent or50 years was the start of the conservation tillage (CT) semi-permanent organic soil cover. This can be amovement and, today, a large percentage of agricul- growing crop or dead mulch. Its function is to protecttural land is cropped using these principles. However, the soil physically from sun, rain and wind and to feedin the book ‘No-tillage seeding’, Baker et al. (2002; a soil biota. The soil micro-organisms and soil fauna takesecond edition of this excellent book was published in over the tillage function and soil nutrient balancing.2006) explained ‘As soon as the modern concept of Mechanical tillage disturbs this process. Therefore,reduced tillage was recognized, everyone, it seems, zero or minimum tillage and direct seeding arePhil. Trans. R. Soc. B (2008)
  4. 4. Downloaded from rstb.royalsocietypublishing.org on August 29, 2012 Role of CA in sustainable agriculture P. R. Hobbs et al. 545Table 1. Extent of no-tillage adoption worldwide. (adapted reduction in wind and water erosion (Van Doran &from Derpsch 2005; ÃÃ includes area in India, Pakistan, Allmaras 1978; Unger et al. 1988). Bissett & O’LearyBangladesh and Nepal in South Asia.) (1996) showed that infiltration of water under long- term (8–10 years) conservation tillage (zero and sub- area under no-tillage (Mha) surface tillage with residue retention) was highercountry 2004/2005 compared to conventional tillage (frequent plowing plus no residue retention) on a grey cracking clay and aUSA 25.30 sandy loam soil in south-eastern Australia. AllmarasBrazil 23.60Argentina 18.27 et al. (1991) reviewed much of the literature on CT upCanada 12.52 to that time and goes on to describe a whole array ofAustralia 9.00 CT-planting systems operating in the US, theirParaguay 1.70 adoption and benefits.Indo-Gangetic Plains (ÃÃ) 1.90 This paper will not go into detail about other soil-Bolivia 0.55 conserving practices that are used throughout theSouth Africa 0.30 world and over time, like terracing or contour bundsSpain 0.30 that are essentially designed to prevent soil erosion onVenezuela 0.30 sloping lands. Lal (2001) described some of theseUruguay 0.26 systems and notes that the effectiveness of theseFrance 0.15 systems depends on proper construction and regularChile 0.12Colombia 0.10 maintenance; if not done properly degradation can beChina 0.10 catastrophic.others (estimate) 1.00 Kumar & Goh (2000) reviewed the effect of croptotal 95.48 residues and management practices on soil quality, soil nitrogen dynamics and recovery and crop yield. The important elements of CA. A varied crop rotation is review concluded that crop residues of cultivated crops also important to avoid disease and pest problems. are a significant factor for crop production through (see FAO web site) their effects on soil physical, chemical and biological functions as well as water and soil quality. They can Data reported by Derpsch (2005) indicate that the have both positive and negative effects, and the role ofextent of no-tillage adoption worldwide is just over agricultural scientists is to enhance the positive effects.95 Mha. This figure is used as a proxy for CA although This paper will restrict the discussion of crop residuesnot all of this land is permanently no-tilled or has to their benefits when used as mulch. Crop residuespermanent ground cover. Table 1 details the extent of result when a previous crop is left anchored or loose afterno-tillage by country worldwide. Six countries have harvest or when a cover crop (legume or non-legume) ismore than 1 Mha. South America has the highest grown and killed or cut to provide mulch. Externallyadoption rates and has more permanent NT and applied mulch in the form of composts and manures canpermanent soil cover. Both Argentina and Brazil had also be applied, although the economics of transport ofsignificant lag periods to reach 1 Mha in the early 1990s this bulky material to the field may restrict its use toand then expanded rapidly to the present-day figures of higher-value crops like vegetables.18.3 and 23.6 Mha, respectively, for these countries. The energy of raindrops falling on a bare soil result inBy adopting the no-tillage system, Derpsch (2005) destruction of soil aggregates, clogging of soil pores andestimated that Brazil increased its grain production by rapid reduction in water infiltration with resulting run-67.2 million tons in 15 years with additional revenue of off and soil erosion. Mulch intercepts this energy and10 billion dollars. Derpsch also estimated that at an protects the surface soil from soil aggregate destruction,average rate of 0.51 t haK1 yrK1 Brazil sequestered 12 enhances the infiltration of water and reduces the loss ofmillion tons of carbon on 23.6 Mha of no-tillage land. soil by erosion (Freebairn & Boughton 1985; McGregorTractor use is also significantly reduced saving millions et al. 1990; Dormaar & Carefoot 1996). Topsoil losses ofof litres of diesel. 46.5 t haK1 have been recorded with TTon sloping land The three key principles of CA are permanent after heavy rain in Paraguay compared with 0.1 t haK1residue soil cover, minimal soil disturbance and crop under NT cultivation (Derpsch & Moriya 1999). NTrotations. The FAO recently added controlled traffic to plus mulch reduces surface soil crusting, increases waterthis list. Each of these will be briefly dealt with before infiltration, reduces run-off and gives higher yield thanproviding some case studies. Table 2 shows a compari- tilled soils (Cassel et al. 1995; Thierfelder et al. 2005).son of CA with CT and traditional tillage (TT). Similarly, the surface residue, anchored or loose, protects the soil from wind erosion (Michels et al.(a) Permanent or semi-permanent organic 1995). The dust bowl is a useful reminder of the impactssoil cover of wind and water erosion when soils are left bare.Unger et al. (1988) reviewed the role of surface residues Surface mulch helps reduce water losses from theon water conservation and indicates that this associ- soil by evaporation and also helps moderate soilation between surface residues, enhanced water temperature. This promotes biological activity andinfiltration and evaporation led to the adoption of CT enhances nitrogen mineralization, especially in theafter the 1930s dust bowl problem. Research since that surface layers (Dao 1993; Hatfield & Pruegar 1996).time has documented beyond doubt the importance of This is a very important factor in tropical and sub-surface residues on soil water conservation and tropical environments but has been shown to be aPhil. Trans. R. Soc. B (2008)
  5. 5. Downloaded from rstb.royalsocietypublishing.org on August 29, 2012546 P. R. Hobbs et al. Role of CA in sustainable agricultureTable 2. A comparison of tillage, conservation tillage (CT) and conservation agriculture (CA) for various issues.issues traditional tillage (TT) conservation tillage (CT) conservation agriculture (CA)practice disturbs the soil and leaves reduces the soil disturbance minimal soil disturbance and soil surface a bare surface in TT and keeps the soil permanently covered coverederosion wind and soil erosion: wind and soil erosion: wind and soil erosion: the least of the maximum reduced significantly threesoil physical health the lowest of the three significantly improved the best practice of the threecompaction used to reduce compaction reduced tillage is used to compaction can be a problem but use of and can also induce it by reduce compaction mulch and promotion of biological destroying biological pores tillage helps reduce this problemsoil biological health the lowest of the three owing moderately better soil more diverse and healthy biological to frequent disturbance biological health properties and populationswater infiltration lowest after soil pores clogged good water infiltration best water infiltrationsoil organic oxidizes soil organic matter soil organic build-up soil organic build-up in the surface layers matter and causes its loss possible in the surface even better than CT layersweeds controls weeds and also reduced tillage controls weeds are a problem especially in the causes more weed seeds weeds and also exposes early stages of adoption, but problems to germinate other weed seeds for are reduced with time and residues germination can help suppress weed growthsoil temperature surface soil temperature: surface soil temperature: surface soil temperature: moderated the more variable intermediate in variability mostdiesel use and costs diesel use: high diesel use: intermediate diesel use: much reducedproduction costs highest costs intermediate costs lowest coststimeliness operations can be delayed intermediate timeliness of timeliness of operations more optimal operationsyield can be lower where planting yields same as TT yields same as TT but can be higher if delayed planting done more timelyhindrance in temperate climates due to delays in soil Cover crops contribute to the accumulation ofwarming in the spring and delayed germination organic matter in the surface soil horizon (Roldan et(Schneider & Gupta 1985; Kaspar et al. 1990; Burgess al. 2003; Alvear et al. 2005; Diekow et al. 2005;et al. 1996; Swanson & Wilhelm 1996). Fabrizzi et al. Madari et al. 2005; Riley et al. 2005), and this effect is(2005) showed that NT had lower soil temperatures in increased when combined with NT. Mulch also helpsthe spring in Argentina, but TT had higher maximum with recycling of nutrients, especially when legumetemperatures in the summer, and that average cover crops are used, through the association withtemperatures during the season were similar. below-ground biological agents and by providing Karlen et al. (1994) showed that normal rates of food for microbial populations. Greater carbon andresidue combined with zero-tillage resulted in better nitrogen were reported under no-tillage and CTsoil surface aggregation, and that this could be compared with ploughing ( TT; Campbell et al. 1995,increased by adding more residues. Recent papers 1996a,b). Others have shown that this is restricted toconfirm this observation; Madari et al. (2005) showed the surface horizons, and that the reverse occurs atthat NT with residue cover had higher aggregate greater depths in humid soils of eastern Canadastability, higher aggregate size values and total organic (Angers et al. 1997). Schultz (1988) showed that Ccarbon in soil aggregates than TT in Brazil; Roldan and N declined by 6% with burning but increased byet al. (2003) showed that after 5 years of NT maize in 1% with stubble retention. Vagen et al. (2005)Mexico, soil wet aggregate stability had increased over concluded that the largest potential for increasingconventional tillage (TT) as had soil enzymes, soil SOC is through the establishment of natural ororganic carban (SOC) and microbial biomass (MBM). improved fallow systems (agroforestry) with attainableThey conclude that NT is a sustainable technology. C accumulation rates from 0.1 to 5.3 Mg C haK1 yrK1. A cover crop and the resulting mulch or previous They continue to say that in cropland, addition ofcrop residue help reduce weed infestation through crop residues or manure in combination with NT cancompetition and not allowing weed seeds the light yield attainable C accumulation rates up tooften needed for germination. There is also evidence of 0.36 Mg C haK1 yrK1. SOC is a key indicator of soilallelopathic properties of cereal residues in respect to quality and Lal (2005) calculated that increasing SOCinhibiting surface weed seed germination (Steinsiek by 1 Mg haK1 yrK1 can increase food grain produc-et al. 1982; Lodhi & Malik 1987; Jung et al. 2004). tion by 32 million Mg yrK1 in developing countries.Weeds will be controlled when the cover crop is cut, Heenan et al. (2004) in Australia showed that changesrolled flat or killed. Farming practice that maintains in SOC at the surface ranged from a loss of 8.2 t haK1soil micro-organisms and microbial activity can also for continuous tilled cereals and residues burnt to alead to weed suppression by the biological agents gain of 3.8 t haK1 where stubble was retained and soil(Kennedy 1999). no-tilled. Nitrogen content followed similar trends. IfPhil. Trans. R. Soc. B (2008)
  6. 6. Downloaded from rstb.royalsocietypublishing.org on August 29, 2012 Role of CA in sustainable agriculture P. R. Hobbs et al. 547the rotation included a legume, SOC accumulation and, in fact, combining these two practices is importantwas the highest. for obtaining the best results. The following comparisons Soil microbial biomass (SMB) has commonly been between tillage and zero-tillage systems are made toused to assess below-ground microbial activity and is a highlight some other benefits not mentioned above.sink and source for plant nutrients. Amendments such Tractors consume large quantities of fossil fuels thatas residues and manures promote while burning and add to costs while also emitting greenhouse gases (mostlyremoval of residues decrease SMB (Doran 1980; CO2) and contributing to global warming when used forCollins et al. 1992; Angers et al. 1993a,b; Heenan ploughing (Grace et al. 2003). Animal-based tillageet al. 2004; Alvear et al. 2005). Balota et al. (2004) in systems are also expensive since farmers have to maintainBrazil in a 20-year experiment showed that residue and feed a pair of animals for a year for this purpose.retention and NT increased total C by 45% and SMB Animals also emit methane, a greenhouse gas 21 timesby 83% at 0–50 cm depth compared with TT. Soon & more potent for global warming than carbon dioxideArshad (2005) showed that SMB was greater with NT (Grace et al. 2003). Zero-tillage reduces these costs andthan TT by 7–36%; frequent tillage resulted in a emissions. Farmer surveys in Pakistan and India showdecrease in both total and active MBC. Increased SMB that zero-till of wheat after rice reduces costs ofoccurs rapidly in a few years following conversion to production by US$60 per hectare mostly due to lessreduced tillage (Ananyeva et al. 1999; Alvarez & fuel (60–80 l haK1) and labour (Hobbs & Gupta 2004).Alvarez 2000). Increased MBM increased soil aggre- Tillage takes valuable time that could be used forgate formation, increased nutrient cycling through slow other useful farming activities or employment. Zero-release of organically stored nutrients and also assisted tillage minimizes time for establishing a crop. The timein pathogen control (Carpenter-Boggs et al. 2003). required for tillage can also delay timely planting of Cover crops help promote biological soil tillage crops, with subsequent reductions in yield potentialthrough their rooting; the surface mulch provides food, (Hobbs & Gupta 2003). By reducing turnaround timenutrients and energy for earthworms, arthropods and to a minimum, zero-tillage can get crops planted onmicro-organisms below ground that also biologically time, and thus increase yields without greater inputtill soils. Use of deep-rooted cover crops and biological cost. Turnaround time in this rice–wheat system fromagents (earthworms, etc.) can also help to relieve rice to wheat varies from 2 to 45 days, since 2–12 passescompaction under zero-tillage systems. There is a lot of of a plough are used by farmers to get a good seedbedliterature that looks at the effects of burning, incorpor- (Hobbs & Gupta 2003). With zero-till wheat this timeation and removal of crop residues on soil properties, is reduced to just 1 day.and much less where mulch is left on the surface. An Tillage and current agricultural practices result inearly paper by McCalla (1958) showed that bacteria, the decline of soil organic matter due to increasedactinomycetes, fungi, earthworms and nematodes were oxidation over time, leading to soil degradation, loss ofhigher in residue-mulched fields than those where theresidues were incorporated. More recent studies also soil biological fertility and resilience (Lal 1994).show more soil fauna in no-tillage, residue-retained Although this SOM mineralization liberates nitrogenmanagement treatments compared with tillage plots and can lead to improved yields over the short term,(Kemper & Derpsch 1981; Nuutinen 1992; Hartley there is always some mineralization of nutrients andet al. 1994; Karlen et al. 1994; Buckerfield & Webster loss by leaching into deeper soil layers. This is1996; Clapperton 2003; Birkas et al. 2004; Riley et al. particularly significant in the tropics where organic2005). Tillage disrupts and impairs soil pore networks matter reduction is processed more quickly, with lowincluding those of mycorrhizal hyphae, an important soil carbon levels resulting only after one or twocomponent for phosphorus availability in some soils decades of intensive soil tillage. Zero-tillage, on the(Evans & Miller 1990; McGonigle & Miller 1996). other hand, combined with permanent soil cover, hasZero-tillage thus results in a better balance of microbes been shown to result in a build-up of organic carbon inand other organisms and a healthier soil. the surface layers (Campbell et al. 1996a; Lal 2005). Ground cover promotes an increase in biological No-tillage minimizes SOM losses and is a promisingdiversity not only below ground but also above ground; strategy to maintain or even increase soil C and Nthe number of beneficial insects was higher where there stocks (Bayer et al. 2000).was ground cover and mulch (Kendall et al. 1995; Jaipal Although tillage does afford some relief fromet al. 2002), and these help keep insect pests in check. compaction, it is itself a major cause of compaction, Interactions between root systems and rhizobacteria especially when repeated passes of a tractor are made toaffect crop health, yield and soil quality. Release of prepare the seedbed or to maintain a clean fallow. Zero-exudates by plants activate and sustain specific tillage reduces dramatically the number of passes overrhizobacterial communities that enhance nutrient the land and thus compaction. However, naturalcycling, nitrogen fixing, biocontrol of plant pathogens, compaction mechanisms and the one pass of aplant disease resistance and plant growth stimulation. tractor-mounted zero-till drill will also result inSturz & Christie (2003) gave a review of this topic. compaction. The FAO CA web site now includesGround cover would be expected to increase biological ‘controlling in-field traffic’ as a component of CA; thisdiversity and increase these beneficial effects. is accomplished by having field traffic follow permanent tracks. This can also be accomplished using a ridge-till(b) Minimal soil disturbance or permanent bed planting system rather than plantingMany of the benefits of minimal soil disturbance were on the flat (Sayre & Hobbs 2004). Some farmers feelmentioned in the above section on permanent soil cover, that sub-soiling or chiselling may be needed to resolvePhil. Trans. R. Soc. B (2008)
  7. 7. Downloaded from rstb.royalsocietypublishing.org on August 29, 2012548 P. R. Hobbs et al. Role of CA in sustainable agriculturebelow-ground compaction layers before embarking on these critical soil organisms are needed. A review ofa NT strategy, especially in drier areas. IPM in CA can be found in Leake (2003). Higher bulk densities and penetration resistancehave been reported under zero-tillage compared withtillage (Gantzer & Blake 1978) and are described asnatural for zero-tillage. This problem is greater in soils 5. EQUIPMENT FOR CONSERVATIONwith low-stability soil aggregates (Ehlers et al. 1983). AGRICULTUREBautista et al. (1996) working in a semi-arid ecosystem Before going on to describe a couple of case studies fromfound that zero-tillage plus mulch reduced bulk density Asia and Mexico, there is a need to discuss the critical(BD). The use of zero-till using a permanent residue importance of equipment for success with CA; zero-tillcover, even when BD was higher, resulted in higher and CA are bound to fail if suitable equipment is notinfiltration of water in NT systems (Shaver et al. 2002; available to drill seed into residues at the proper depthSayre & Hobbs 2004). Scientists hypothesized that for good germination. It is urgent that CA equipment iscontinued use of reduced, shallow and zero-tillage perfected, available and adopted for this new farmingwould require a shift to short-term TT to correct soil system. Iqbal et al. (2005) studied NT under drylandproblems. However, Logsdon & Karlen (2004) showed conditions in Pakistan and showed that NT gave lowerthat BD is not a useful indicator and confirm that yields than TT, but the experiment was planted withfarmers need not worry about increased compaction improper equipment and with no mention of residuewhen changing from TT to NT on deep loess soils in management; the results are therefore suspect.USA. Fabrizzi et al. (2005) also showed higher BD and There are some excellent reviews of the equipmentpenetration resistance in NT experiments in Argentina, needs for zero-tillage systems. Baker et al. (2002, 2006)but the values were below thresholds that could affect devoted an entire book to this topic. A book on CAcrop growth; wheat yields were the same as in the tilled (‘Environment, farmer experiences, innovations andtreatments. This experiment left residues on the socio-economic policy’) edited by Garcia-Torres et al.surface in NT. The authors concluded that the (2003) has several papers on equipment for small- andexperiment had a short time frame and more time large-scale farmers. The main requirements of equip-was needed to assess the effect on BD. ment in a CA system are a way to handle loose straw The role of tillage on soil diseases is discussed by Leake (cutting or moving aside), seed and fertilizer place-(2003) with examples of the various diseases affected by ment, furrow closing and seed/soil compaction. Theretillage. He concluded that the role of tillage on diseases is is also a need for small-scale farmers to adapt direct-unclear and acknowledges that a healthy soil with high drill seeding equipment to manual, animal or smallmicrobial diversity does play a role by being antagonistic tractor power sources (reduced weight and draftto soil pathogens. He also suggested that NT farmers requirements) and reduce costs, so equipment isneed to adjust management to control diseases through affordable by farmers, although use of rental andsowing date, rotation and resistant cultivars to help shift service providers allows small-scale farmers to usethe advantage from the disease to the crop. A list of the this system even if they do not own a tractor or a seeder.impacts of minimum tillage on specific crops and their A simple three-row small grain seeder has beenassociated pathogens can be found in Sturz et al. (1997). developed for small-scale animal-powered farmers in An added economic consideration is that tillage Bolivia (Wall et al. 2003). This equipment uses a shovelresults in more wear and tear on machinery and higher rather than a disc opener to save weight. It has strawmaintenance costs for tractors than under zero-tillage wheels attached to the coulter to help move residuessystems. aside and reduce clogging. It also has the benefit that it can be used in ploughed or unploughed soil. The main(c) Rotations benefit farmers mentioned about this drill was savings inCrop rotation is an agricultural management tool with time; it takes 10 h to plant a hectare with this machineryancient origins. Howard (1996) reviewed the cultural and 12 days for the TT and seeding method. Thecontrol of plant diseases from an historical view and conventional system also required the farmer to walkincluded examples of disease control through rotation. 100 km haK1 to undertake all the tillage and seedingThe rotation of different crops with different rooting with his animals. The stand with the new drill was 246Gpatterns combined with minimal soil disturbance in 37 plants mK2 compared with 166G39 for the conven-zero-till systems promotes a more extensive network of tional system. The cost of the drill was only $330–390 inroot channels and macropores in the soil. This helps in Bolivia. Similar information was provided by Ribeirowater infiltration to deeper depths. Because rotations (2003) for planters in Brazil. These can be manuallyincrease microbial diversity, the risk of pests and applied jabber planters to animal-drawn planters. Indisease outbreaks from pathogenic organisms is both countries, the participation of farmers, localreduced, since the biological diversity helps keep manufacturers and extensionists was vital for success.pathogenic organisms in check (Leake 2003). The Saxton & Morrison (2003) looked at equipmentdiscussion of the benefits of rotations will be handled in needs for large-scale farmers where tractor horsepower,other chapters of this publication. weight and draft are less important. Earlier machines Integrated pest management (IPM) should also be were developed for clean tilled farm fields, whereas newadded to the CA set of recommendations, since if one NT machines provide precision seed placement throughof the requirements is to promote soil biological consistent soil penetration and depth and also supplyactivity, minimal use of toxic pesticides and use of fertilizer in bands which is crucial for minimizingalternative pest control methods that do not affect nutrient losses in zero-till systems. This paper discussesPhil. Trans. R. Soc. B (2008)
  8. 8. Downloaded from rstb.royalsocietypublishing.org on August 29, 2012 Role of CA in sustainable agriculture P. R. Hobbs et al. 549the use of disc openers versus hoe and chisel openers and 3.0the use of additional straw and chaff spreading devices. 2430 2.5 millions of hectares 19106. CASE STUDY FROM THE RICE–WHEAT 2.0SYSTEMS OF SOUTH ASIA 1.5(a) Case study from Asia 1156The first case study looks at the 13.5 Mha of the rice– 1.0wheat systems of the Indo-Gangetic Plains for South Asia 561(RWC web site: http://www.rwc.cgiar.org/RWC-Crop. 0.5 209asp). The traditional cultivation technique used for 0.022 0.255 2.1 12.8 71growing rice in this system, and also in much of the rice 0 1996– 1997– 1998– 1999– 2000– 2001– 2002– 2003– 2004– 2005–growing regions of Asia, is wet ploughing of soils in the 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006main rice field (puddling), followed by transplantation of yearsrice seedlings grown in separate seedbeds. Interestingly,this system of rice cultivation is often cited as being used Figure 1. Estimated area growth of no-till wheat in the Indo- Gangetic Plains for the past 10 years (adapted from Rice–for centuries without declining productivity. However, it Wheat Consortium (RWC) for the Indo-Gangetic Plainswas at relatively low subsistence rice yield levels. There (2006). http://www.rwc.cgiar.org).are several excellent reviews of a number of Asian long-term experiments using modern varieties on this issue, and decline in wheat yield potential, plus many othersome rice–wheat and others rice–rice, with some showing negative effects (Hobbs & Gupta 2003, 2004).yield declines while others do not (Cassman et al. 1995; The solution for late planting and problems ofAbrol et al. 1997; Dawe et al. 2000). delayed turnaround from rice harvest to wheat planting Puddling was done by farmers over the centuries for came from the introduction of zero-tilled wheat intovery specific reasons, the most important being to help rice stubbles that started in the region in the mid-control weeds; farmers found that keeping soils 1980s. Efforts to adapt and promote resource conser-anaerobic and flooded reduced weed problems and ving technologies (RCTs that include NT) in the Indo-also hand weeding was easier with these softened soils. Gangetic Plains (IGP) have been underway for nearlyThe puddling essentially reduced water percolation three decades, but it is only in the past 4–5 years thatand infiltration and ponded the water on the surface. the technologies are finding accelerated acceptance byLess is written on the puddling effect on soil biological the farmers (figure 1). The spread of NT is taking placeproperties although some work is available from in the irrigated RW regions but is yet to be rooted in theresearch done at IRRI in the 1990s (Reichardt et al. rainfed agro-ecoregions. In the last 2004–2005 wheat1997, 2001). The authors conclude that SMB plays a season, it was estimated that nearly 2 Mha of zero-tillsignificant role as a passive nutrient pool and suggests wheat was being grown by 425 000 farmers in the fourthat its reduction, found in puddled soils in the second South Asian countries (RWC Highlights 2005: http://half of the cropping season, could be a mechanism that www.rwc.cgiar.org/Pub_Info.asp?IDZ152); bothcontributes to declining productivity in continuous rice large- and small-scale farmers adopted this technologycropping systems. Little has been published on soil with small-scale farmers renting zero-till drill servicesmicrobes in rice–wheat systems. from service providers. The key to this rapid adoption When modern varieties of wheat and rice were in the last 5 years was the use of farmer participatoryintroduced to South Asia in the 1960s, farmers in approaches to allow farmers to experiment with theNorthwest India and Pakistan introduced rice into their technology in their own fields and promotion of thewheat systems and farmers in the eastern side of South local machinery manufacturers in the region to beAsia introduced wheat into their rice systems; wheatwas grown in the cool dry season and rice in the warm partners in the programme; cheap, affordable, effectivewet monsoon months. This intensified the system that drills are available based on the use of the inverted Thas grown to 13.5 Mha since the 1960s. It is now one of coulter technology that was introduced into India andthe most important cropping systems for food security Pakistan from New Zealand.in South Asia along with rice–rice systems. One of the One major need of this system is the developmentmain issues that confronted farmers when this new and availability of equipment that will allow goodsystem was introduced and found feasible and profit- germination of rice and wheat while, at the same time,able was the soil physical properties left after harvest of minimizing soil disturbance and sowing the seed anda puddled transplanted rice crop. The effect of banded fertilizer into loose and anchored stubbles. Thepuddling reduced soil structure, especially stable soil RWC members are working vigorously in partnershipaggregates, and led to formation of compaction layers with local manufacturers and farmers to make new(Hobbs et al. 1993). Soil cracking was higher under equipment available for experimentation at an afford-intensive puddling (Mohanty et al. 2004). Unpuddled able price, with provisions for after-sales service anddirect-seeded rice maintained the soil in a better supply of needed spare parts to make this systemphysical condition, although yields were lower where successful. Recently, multicrop zero-till ferti-seed drillsweeds were not controlled. Farmers ploughed their fitted with inverted T openers, disc planters, punchfields many times to obtain a suitable seedbed for planters, trash movers or roto-disc openers have beenplanting wheat (Hobbs & Gupta 2003, table 7.1). This developed for seeding into loose residues (RWCploughing takes time and often results in late planting Highlights 2004–2005; figure 2).Phil. Trans. R. Soc. B (2008)
  9. 9. Downloaded from rstb.royalsocietypublishing.org on August 29, 2012550 P. R. Hobbs et al. Role of CA in sustainable agriculture technology intercrops direct-seeded rice with a green (a) (b) (c) manure (Sesbania aculeata). After a month, the crop is sprayed with 2,4-D herbicide to knock down the green manure and kill any germinating broadleaf weeds. The dying weeds and GM provide nutrients to the rice crops as they decompose, but new weeds are suppressed by the ground cover and allelopathic properties of the (d) (e) (f) mulch. The results look good and this research will be reported soon. In addition to zero-till rice and wheat, attempts are also being made to diversify the cropping systems by introducing other crops into new rotations that help break disease and insect cycles and provide more income and diversity for farmers. This may help with some other problems that have surfaced whenFigure 2. Various equipments for planting wheat no-till in rice is shifted from anaerobic to aerobic systems.RWC. (a) inverted T coulter, (b) Indian no-till drill using Widespread infestations of the root knot nematodeinverted T, (c) disc-type planter, (d ) star-wheel punch (Meloidyogyne graminicola) on rice were found whenplanter, (e) ‘happy planter’ where straw picked up and direct-seeded rice was grown instead of puddled rice inblown behind seeder and ( f ) disc planter with trash mover. Bangladesh (Padgham et al. 2004). Many advantages have been mentioned and charac-terized for this innovation including US$145 million (b) Case study from Mexico Maize–wheat cropping patterns are common in thesavings in fuel costs (2004 costs) and the benefits of less irrigated northwest areas of Mexico and the rainfedgreenhouse gas emissions, less weeds, more beneficial areas of the altiplano areas of central Mexico. In bothinsect activity, improved water use efficiency, and also situations, the major limiting factor is moisture. Thisimportant higher yields at less cost, improved incomes case study introduces the concept of permanent bedfrom wheat and savings in time that can be used for systems for addressing efficient use of water. In bedother productive uses (Hobbs & Gupta 2004). It is systems, soil is raised in a ridge-and-furrow configu-anticipated that as machinery manufacturers keep pace ration. These bed systems involved tillage to preparewith demand for drills, as the message about the the soil before making the beds. However, manybenefits of zero-till wheat reaches more farmers, and as traditional bed planting systems did not receive tillage;farmer mindsets about the need for tillage are over- the chinampas of pre-Colombian Mexico and the warucome that the acreage for this innovation will cover the warus of Peru and Bolivia used crop residue mulchingbulk of the wheat planted after rice in South Asia. or only superficial tillage ( Thurston 1992). Bed However, the story does not end here. In order for systems reduce compaction in the rooting zone bythe benefits of zero-tilled wheat to be seen in the entire confining wheel traffic to the furrow bottoms. The casesystem and for soil physical and biological health to study described here from Mexico looks at the results ofimprove and the rice–wheat system to become more using a permanent bed planting maize–wheat systemsustainable, rice practices will also have to change. A where soil disturbance is minimized, crop residues aremove is already afoot in the rice–wheat consortium retained on the surface from previous crops andpartners (national and international programmes) to reshaping of beds is done only as needed betweenresearch, experiment and promote a move to zero-till crop cycles (Limon-Ortega et al. 2002).direct-seeded rice: a more aerobic rice system that does The experiment used for this paper was undertakenaway with puddling of soils. These aerobic systems are by the International Maize and Wheat Improvementbased on direct-seeded rice systems on either the flat or Center (CIMMYT) in the State of Sonora in North-raised beds, with and without tillage and with or west Mexico. Farmers have 225 000 hectares ofwithout transplanting (RWC DSR paper: http://www. irrigated land in this area with maize, sorghum,rwc.cgiar.org/Pub_Info.asp?IDZ123). The ultimate soybean, safflower, dry beans, cotton and wheat, thesystem would allow farmers to grow zero-till rice major crops. Ninety-five per cent of the farmers nowfollowed by zero-till wheat. Wheat yields are best grow crops on beds with farmers changing from theafter direct-seeded rice without puddling (DSNP; conventional planting on the flat with basin irrigation inHobbs et al. 2002; Tripathi et al. 2005). the last 20 years (Aquino 1998). This change was a Various national and international research and result of water shortages from the water storagebreeding agencies are now exploring aerobic rice reservoir system; farmers had to find more efficient(Bouman et al. 2002). The main issue to resolve relates water use systems in order to expand acreage. Resultsto effective weed control in a non-puddled rice system. suggest that bed planted systems need 29% lessVarious innovative integrated ways are being sought to water than flat planting systems for an 8% higher yieldhandle this problem, including use of cover crops and (Sayre & Hobbs 2004). Most of the farmers still use TTmulches, more competitive rice varieties against weeds to remake the beds for each new crop, but results that areand use of selective herbicides. Availability of roundup- reported below suggest that use of permanent bedready transgenic rice and/or development of cultivars systems where tillage is minimized and crop residuessuited to direct seeding with zero-till drills, having early are left on the surface will be more sustainable.vigour and competitive with weeds, would go a long The treatments in this long-term trial were asway to help resolve this issue. One encouraging follows.Phil. Trans. R. Soc. B (2008)
  10. 10. Downloaded from rstb.royalsocietypublishing.org on August 29, 2012 Role of CA in sustainable agriculture P. R. Hobbs et al. 551 (i) CT with formation of new beds for each crop of 0.5 Pg C yrK1. Climate change is likely to strongly and with all the crop residues incorporated. affect rice–wheat, rice–rice and maize-based cropping (ii) Permanent beds with all the residues burned. systems that, today, account for more than 80% of the (iii) Permanent beds with 30% of the residues total cereals grown on more than 100 Mha of retained on the surface and the rest baled for agricultural lands in South Asia. Global warming may fodder. be beneficial in some regions, but harmful in those (iv) Permanent beds with the maize residue baled for regions where optimal temperatures already exist; an fodder and the wheat residue retained. example would be the rice–wheat mega-environments (v) Permanent beds with all the residues retained. in the IGP that account for 15% of global wheat production. Agronomic and crop management prac- A detailed account of this experiment can be found tices have to aim at reducing CO2 and other green-in Sayre & Hobbs (2004). Yield differences were small house gas emissions by reducing tillage and residuein the first 5 years supporting the idea that some burning and improving nitrogen use efficiency. In thetransitional years are needed before changes occur in IGP, resource-conserving technologies continue tosoil properties with changes in management. Changes expand in the rice–wheat cropping systems and savestarted to appear between treatments in the sixth and 50–60 l of diesel haK1 plus labour, and significantlysubsequent years with the permanent bed treatment reduce release of CO2 to the environment. Methanewith all the residues retained the best and highest emissions that have a warming potential 21 times thatyielding plot, and the permanent bed treatment with of CO2 are common and significant in puddledresidues burnt the worst and lowest yielding plot. The anaerobic paddy fields and also when residues aretreatment with CT with residues incorporated was burnt. This GHG emission can be mitigated by shiftingstatistically at par with the best permanent bed system to an aerobic, direct seeded or NT rice system. A reviewbut incurred higher costs for land preparation. of the other benefits of direct seeding and NT in RW Organic matter, nitrogen levels, surface soil aggre- areas of South Asia can be found in Grace et al. (2003).gate size and SMB were higher in the permanent beds Nitrous oxide has 310 times the warming potential ofwith residue retention. One valuable insight from this carbon dioxide, and its emissions are affected by poorexperiment was the lower soil strength/compaction in nitrogen management. Sensor-based technologies forall treatments, except the one where residues were measuring normalized differential vegetative index andburned. The addition of the residue plays a significant moisture index have been used in Mexico and Southrole in reducing compaction at the soil surface and Asia to help improve the efficiency of applied nitrogenincreasing water infiltration in minimal tilled plots. and reduce nitrous oxide emissions.Similar data confirmed this finding in a similar maize–wheat long-term experiment under rainfed conditionsin the altiplano areas near Mexico City (Govaerts et al. 8. CONCLUSIONS2005). In this rainfed experiment, zero-tilled plots with Crop production in the next decade will have toresidue retention resulted in higher and more stable produce more food from less land by making moreyields than conventionally tilled plots with residues efficient use of natural resources and with minimalincorporated. Zero-tilled plots without residue reten- impact on the environment. Only by doing this willtion had much reduced yields. In the same experiment, food production keep pace with demand and thepermanent raised beds combined with rotation and productivity of land be preserved for future gener-residue retention yielded the same as zero-tilled plots ations. This will be a tall order for agriculturalwith residue retention. The bed system gave farmers an scientists, extension personnel and farmers. Use ofadded advantage of being able to use more varied weed productive but more sustainable management practicesand fertilizer practices. described in this paper can help resolve this problem. Larger-scale demonstrations have been planted Crop and soil management systems that help improveon farmer’s fields. The permanent beds averaged soil health parameters (physical, biological and7.2 t haK1 compared with 6.2 t haK1 for the conven- chemical) and reduce farmer costs are essential.tionally made beds. The data also show that average Development of appropriate equipment to allow thesereturns over variable costs increased by 75% for the systems to be successfully adopted by farmers is a pre-permanent bed system with residue retention requisite for success. Overcoming traditional mindsetscompared with the conventional tilled treatment. The about tillage by promoting farmer experimentationimportance of suitable equipment that will allow seeding with this technology in a participatory way will helpof crops into permanent beds with residue retention accelerate adoption. Encouraging donors to supportcannot be overemphasized. Systems based on discs, this long-term applied research with sustainablepunch planters and strip tillage are being experimented funding is also an urgent requirement.with in Mexico and South Asia (Sayre & Hobbs 2004). REFERENCES7. CLIMATE CHANGE AND CONSERVATION Abrol, I. P., Bronson, K. F., Duxbury, J. M. & Gupta R. K.AGRICULTURE (eds) 1997 Long-term soil fertility experiments in rice–Lal (2005) suggested that by adopting improved wheat cropping systems. In Proc. Workshop, 15–18 Octobermanagement practices on agricultural land (use of 1996, Surajkund, Haryana, India. New Delhi, India,NT and crop residues), food security would not only be Consortium paper series 1, pp. 23. 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