doi:10.2489/jswc.70.5.103A

FEATURE Conservation tillage is not conservation agriculture Don C. Reicosky

A LOOMING COLLISION: GLOBAL words, is the heart of global sustainability” burrowing animals, etc.) that accomplish POPULATION AND FOOD SECURITY (Diamond 2005). many biochemical transformations—from As world population increases and food Approaches to soil conservation are fixing atmospheric nitrogen (N) to the production demands rise, keeping our soil in constant evolution and improvement decomposition of organic matter. healthy and productive while protecting (Dumanski and Peiretti 2013). There is also Because the soil is alive, it must be the environment is of paramount impor- a continuum of conservation approaches treated appropriately. For example, mycor- tance for agriculture. The expanding for preparation of soil for planting. At rhiza fungi produce glomalin (glue-like global population—expected to reach 9.5 one extreme, conventional tillage usually substance) that improves the soil struc- billion people by 2050 (United Nations involves aggressive mechanical inversion of ture and pore space over time. Better soil 2014)—is putting tremendous pressure soil that leads to unintended consequences structure allows more rainfall to soak into on the finite land area and resources for of high rates of soil organic carbon (C) the soil profile. Fungi are rather delicate Copyright © 2015 Soil and Water Conservation Society. All rights reserved. agricultural production, and pending cli- loss, disruption of the soil biology, and and populations are reduced with till- Journal of Soil and Water Conservation mate extremes exacerbate the challenge erosion by wind and rain. No-tillage (zero age; however, if the soil is not disturbed, of food security for both developed and tillage) leaves most soil undisturbed, pro- the numbers will increase over time. The developing countries. viding protection from erosion and loss of term “soil health” is preferred by some Despite the lessons of history, soil ero- C to the atmosphere. Conservation tillage (Doran et al. 1996; Doran and Safley sion is still a major problem in agricultural (CT), or “any tillage sequence, the object 1997) because it portrays soil whose func- production systems. Efforts to control land of which is to minimize or reduce loss of tions are mediated by a diversity of living degradation and soil erosion can be traced soil and water; operationally, a tillage or organisms that require management and over the last 10,000 years; humankind has tillage and planting combination which conservation. For farmers, soil health is a been building on the ruins of the past leaves a 30% or greater cover of crop resi- key component of good production. The tillage and monoculture concepts at our due on the surface” (Soil Science Glossary simple slogan “healthy soil, healthy plants peril (Lal et al. 2007; Montgomery 2007a, Terms Committee 2008), is ambiguously and animals, healthy people” is often used 70(5):103A-108A 2007b). Montgomery (2007b) describes intermediate and covers a broad range of to describe the CA system. Understanding the effects of poor soil management and soil disturbance and crop residue incor- that the soil is a living biological system erosion on several past civilizations. Once poration between these two extremes brings the practice of tillage, bent on frac- thriving, these civilizations eventually col- (Derpsch et al. 2014). The objectives of turing and stirring the soil, under scrutiny. lapsed due to erosion, salinization, nutrient this review are to discuss the definition This is especially critical because stirring www.swcs.org depletion, and other types of soil degra- and merits of CT and to illustrate the of the top 5 to 8 cm (2 to 3 in) of soil dation. Tillage for soil preparation for complexities and the benefits of conserva- results in increased runoff. planting and cultivation, by loosening soil tion agriculture (CA) as a sustainable form and easing its transport by wind or water, of agricultural production that can also DEFINITION OF CONSERVATION TILLAGE induces and increases erosion. We are los- contribute to global food security. Conservation tillage includes a broad set ing soil faster than nature can make it. In of practices with a goal leaving some crop fact, Montgomery (2007b) calculated aver- SOILS: A LIVING SYSTEM residue on the soil’s surface to increase age soil formation of 0.017 to 0.036 mm Soils are alive, are extremely complex, and water infiltration and reduce erosion. (0.00067 to 0.00142 in) a year—equiva- play essential roles in our food and water The various practices described as “con- lent to 700 to 1,500 years to form an inch security, ecosystem services, climate change servation tillage” have led to terminology (25 mm) of soil. In Collapse: How Societies adaptation and mitigation, poverty allevia- confusion. Conservation tillage is often Choose to Fail or Succeed, Diamond states tion, and sustainable development, as well confused with no-till or variants of CT that at least 10 of the 12 most important as global environmental change and human described in vague terms, such as such as environmental problems we face “are also evolution on earth. They provide anchorage minimum tillage, mulch tillage, ridge till- central to agronomy, crop science and soil for plant roots, serve as support for plants age, strip tillage, and reduced tillage, where science. Agricultural sustainability, in other to capture C in photosynthesis, hold water planting is achieved on specially prepared long enough for plants to make use of it, surfaces with various amounts of crop and hold and recycle nutrients that sustain residue cover (Hobbs 2007; Dumanski Don C. Reicosky is a research soil scientist emeri- tus, retired from the USDA Agricultural Research life. Soils also serve as a home to numerous and Peiretti 2013; Derpsch et al. 2014). Service, Morris, Minnesota. microorganisms (bacteria, fungi, protozoa, These definitions of CT and the use of nematodes, algae, earthworms, soil insects, jargon send a mixed and confusing mes-

JOURNAL OF SOIL AND WATER CONSERVATION SEPT/OCT 2015—VOL. 70, NO. 5 103A sage (CTIC 1999). Mannering and Fenster number of tillage trips from eight to six. of some nature. Usually, the retention of (1983) define CT as a broad term used Both farmers and researchers are confused 30% surface cover by residues character- with “any” tillage system with the primary by the terminology and its inconsistent use. izes the lower limit of classification for objective of “reducing soil and water loss” Baker et al. (2002) identified 14 names CT, but other conservation objectives and agree that this has caused confusion. for reduced tillage: zero-tillage, chemical- may include conservation of time, fuel, The term most confusing is “minimum plowing, stale-seedbed, chemical fallow, earthworms, soil, water, soil structure, and tillage,” defined as “the minimum use of no-till, direct-seeding, disc drilling, dril- nutrients. Thus, residue levels alone do primary and/or secondary tillage necessary lage, sod-seeding, minimum-tillage/ not adequately describe all CT practices” for meeting crop production requirements reduced-tillage, strip-tillage/zone-tillage, (Baker et al. 2002). under the existing soil and climatic con- ridge-tillage/ridge-till, and residue farm- Conservation tillage suggests reduced ditions, usually resulting in fewer tillage ing. They defined CT as “the collective tillage intensity compared to moldboard operations than for conventional tillage” umbrella term commonly given to no- plow inversion that includes a wide range of (Soil Science Glossary Terms Committee tillage, direct-drilling, minimum-tillage, soil disturbance and residue incorporation. 2008; Mannering and Fenster 1983). To and/or ridge-tillage, to denote that the Examples of CT in the field are illustrated some it could mean merely reducing the specific practice has a ‘conservation goal’ in figure 1. No-till or direct seeding has

Figure 1 Copyright © 2015 Soil and Water Conservation Society. All rights reserved. Journal of Soil and Water Conservation Collection of several different types of “conservation tillage” tools and planters illustrating a wide range of tillage depths and degrees of residue incorporation (from left to right and top to bottom): (a) conventional inversion moldboard plow, (b) paraplow, (c) deep ripper combination tool, (d) deep field cultivator combination tool, (e) field cultivator tool rigid tine (photo courtesy of the Natural Resources Conservation Service [NRCS]), (f) deep field cultivator spring tine (photo courtesy of NRCS), (g) deep field cultiva- tor rigid tine, (h) heavy-duty disk harrow (photo courtesy of NRCS), (i) normal duty disk harrow, (j) shallow field cultivator spring tine, (k) vertical tillage tool (photo courtesy of NRCS), (l) high disturbance strip tillage implement combination tool, (m) strip/zone tillage implement in wheat stubble, (n) strip tillage implement combination tool rigid tine, (o) disc opener no-till planter into alfalfa stubble, and (p) disc opener no-till planter into dead residue (photo courtesy of Dave Brandt).

(a) (b) (c) (d) 70(5):103A-108A

(e) (f) (g) (h) www.swcs.org

(i) (j) (k) (l)

(m) (n) (o) (p)

104A SEPT/OCT 2015—VOL. 70, NO. 5 JOURNAL OF SOIL AND WATER CONSERVATION often been included in the broad class of and redistribute/level the soil surface. The conservation is generally met; however, CT, but perhaps should be considered as a wide range of soil disturbance and residue the soil conditions may be quite varied. separate class for CA with minimum soil incorporation has consequences in fuel con- The confusion with the definition of CT disturbance quantified. When we con- sumption since less fuel is consumed with is illustrated in the conceptual diagram sider the soil as a living system, minimum less soil disturbed. Less residue incorpora- in figure 2. The chart shows the relative soil disturbance and residue incorporation tion provides more soil protection during volume of soil disturbed versus the dif- must be considered to meet the objectives erosion events. Often, characteristics of soil ferent types of tillage/seeding methods. of improved soil health and soil protection. disturbance and residue incorporation are The left side of the chart represents the Strip tillage equipment leaves disturbed not quantified, adding to the confusion and moldboard plow with a large volume of strips of various widths and depths with uncertainty about the extent of soil con- soil disturbed (conventional tillage) that the inter-row undisturbed. Chisel plows servation and research with CT techniques. progressively decreases through several can have rigid or spring tines and typi- The lack of quantitative information types of CT implements to minimum soil cally operate 100 to 150 mm (4 to 6 in) on the volume of soil disturbed and the disturbance with low disturbance no-till/ deep, mixing the soil and leaving some crop degree of residue incorporation or resi- direct seed planters (no-tillage) on the residue on the surface. Using combina- due left on the soil surface in CT has extreme right. Everything in between the tion tools for deep ripping utilizes subsoil been detrimental to the research commu- extremes is considered CT and is not listed shanks that penetrate to about 380 mm (15 nity (Derpsch et al. 2014). The basic goal in quantitative order, reflecting ambigu- Copyright © 2015 Soil and Water Conservation Society. All rights reserved. in) deep and heavy disks to cut the residue of 30% residue cover for soil and water ous definitions. Quantitative data on both Journal of Soil and Water Conservation

Figure 2 Schematic representation of the volume of soil disturbed with a wide range of conservation tillage (CT)/seeding implements from inversion tillage with the moldboard plow on the left to the low disturbance no-till planter on the right. All forms of CT are between these extremes and are listed in a suggested qualitative order. HD = high disturbance and LD = low disturbance. Source: modified after Friedrich Tebrügge.

Increasing crop residues covering soil

Decreasing intensity and frequency of soil disturbance 70(5):103A-108A

Conventional Conservation No tillage tillage tillage www.swcs.org

Moldboard plow Disc plow Deep ripper Subsoil-HD Rotary tillage Chisel plow Field cultivator Ridge till Subsoil-LD tillage Vertical Reduced tillage Mulch tillage Stubble mulch Strip tillage Slot tillage No till-HD No till-LD

+ Tillage soil/residue disturbance continuum Volume soil disturbed Volume

0 Tillage/planting system

JOURNAL OF SOIL AND WATER CONSERVATION SEPT/OCT 2015—VOL. 70, NO. 5 105A volume of soil disturbed and degree of res- study as chisel-plow tillage with straight- The significant soil loss from the CT idue incorporation or residue left on the shanks), and no-till (direct seeding); results treatments suggests that, despite the soil’s surface are needed for better under- are shown in table 1. Conventional plow accepted 30% residue cover, many types standing the conservation benefits of the tillage and disc harrowing had the largest of CT do not adequately protect the resulting disturbed surface because of their sediment loss, CT had intermediate loss, soil from raindrop impact and are not impact on the rate of evaporation, residue and no-till had the least sediment loss. sustainable. Other CT tools would give decomposition, and nutrient cycling in Sediment lost from conventional plow till- varying amounts of soil erosion, based crop production. age was 52 times greater than the no-till on soil volume disturbance and residue Tillage is not something nature does and treatment, while CT was 11 times greater cover. North Dakota State University should not be considered a conservation than the no-till treatment. Extension soil specialist Dave Franzen said, objective (Faulkner 1944). This statement A second example of soil erosion with “Conservation tillage is better, but it is not raises the question, “How has the conser- conservation tillage systems is illustrated good enough.” (Personal communication, vation community accepted and used CT by Dickey et al. (1984). They stated, “the January 7, 2015). Most “conservation till- over the last five decades?” Conservation term ‘conservation tillage,’ as used in age” is more “tillage” than “conservation.” tillage terminology was first used when this paper, includes all tillage methods It makes technical sense, environmental chisel plows were widely used in the late that leave at least 20% of the soil surface sense, financial sense, and common sense 1960s. This tool left more residue on the covered with residues after planting.” A to stop soil erosion to maintain food secu- Copyright © 2015 Soil and Water Conservation Society. All rights reserved. soil’s surface with soil disturbance extent a summary of their two-year data enabled rity. While the goals of CT are laudable, Journal of Soil and Water Conservation function of the operating depth. However, comparison of three different conserva- present-day CT methods are not ade- in many cases multiple tillage trips resulted tion tillage systems with various depths 10 quately protecting our soils. in full width disturbance and little residue to 25 cm (4 to 10 in) deep and degrees of left on the soil’s surface. Regardless, use of residue incorporation that fall between the DEFINITION OF the term “conservation tillage” remained. conventional tillage system (moldboard CONSERVATION AGRICULTURE The phrase “conservation tillage” has plow plus disk harrow) and no-till. As The first use of the phrase “conservation become, at times, an oxymoron; it sends a expected, the residue cover was largest on agriculture” (CA) came out of a Latin- mixed and confusing message and gives a the no-till treatment and decreased to the American Network for Conservation misguided sense of entitlement and con- minimum on the moldboard plow treat- Tillage meeting sponsored by the Food servation because of very “loose limits” ment. Correspondingly, soil loss was largest and Agriculture Organization of the on the definition of soil disturbance and from the moldboard plow treatment and United Nations (FAO) in Morelia, 70(5):103A-108A residue management. Conservation is a lowest from the no-till treatment, show- Michoacán, Mexico, in 1997 (Rolf word to be respected, revered, and used to ing the importance of residue cover. The Derpsch, personal communication, April describe agriculture, not tillage. measured soil erosion showed a decrease 9, 2015). Conservation agriculture was Soil erosion continues to be a major that appeared to be partly related to till- introduced by the FAO (2008) as a con- problem in production agriculture age intensity and partly due to residue cept for resource-efficient agricultural www.swcs.org (Montgomery 2007b). Even with several cover. Even though these treatments were crop production based on integrated types of CT, soil is being lost faster than loosely called conservation tillage, there management of soil, water, and biological nature can make it. Seta et al. (1993) mea- was much more erosion relative to the no- resources combined with external inputs. sured soil erosion after moldboard plow till treatment, in general agreement with It has been promoted by institutions and inversion tillage, CT (practiced in this the work of Seta et al. (1993). organizations with the expectation that it can contribute to sustainable intensifica- Table 1 tion (Hobbs 2007; Hobbs et al. 2008; FAO Soil loss from conventional, conservation, and no-till systems showing total runoff, sed- 2011) and has spread into other regions of iment concentration, sediment loss, and relative sediment loss compared to the no-till the world to become a global agricultural system. Means or totals in a column followed by a different lowercase letter are signifi- movement (Friedrich et al. 2012; Kassam cantly different (p < 0.05). Adapted with permission from table 1 of Seta et al. (1993). et al. 2014b). Recent reviews of CA have been published by Hobbs (2007), Hobbs et Total runoff Sediment concen- Sediment loss Sediment al. (2008), Dumanski et al. (2006), Baker et Tillage type (mm) tration (g L–1) (Mg ha–1) relative loss al. (2006), Goddard et al. (2008), Govaerts Conventional (moldboard 45.0b 36.4c 15.5c 52 et al. (2009); Kassam et al. (2009), Friedrich plowing to a depth of 18 cm et al. (2012), Kassam et al. (2014a), and followed by two diskings) Conservation (chisel-plow 28.9b 12.5b 3.3b 11 Farooq and Siddique (2015). tillage with straight-shank The definition of CA incorporates sys- chisel plow) tem concepts based on three key principles: No tillage (direct seeding) 7.6a 4.7a 0.3a 1 (1) continuous residue cover on the soil surface; (2) continuous minimum soil dis-

106A SEPT/OCT 2015—VOL. 70, NO. 5 JOURNAL OF SOIL AND WATER CONSERVATION turbance (no-tillage); and (3) diverse crop ration with crop residue mulch on the soil has been an educational evolution that rotations and cover crop mixes (Hobbs surface. The synergistic simplicity of no- the scientific community must under- 2007; Hobbs et al. 2008; Kassam et al. 2009; till (minimizes C and soil loss) and the use stand and continue for future generations. FAO 2011; Friedrich et al. 2012; Derpsch of diverse rotations and cover crop mixes Conservation tillage, although well et al. 2014). Soil cover can be either live (maximizes soil coverage and C input) for intentioned, does not always provide cover crops, terminated cover crops, or soil diversity protection and regeneration enough soil erosion protection and water mulches of crop residues remaining after benefits CA. conservation. Present day implementa- previous harvests that accumulate on the Conservation agriculture and soil tion of CA principles and concepts will soil surface. Retaining mulch between health system concepts are closely related be a way to cope with food production crops provides better protection against to C management, and the implementa- during climate extremes. Both the pub- erosion and can also maintain higher soil tion of CA with mostly undisturbed soils, lic and policy groups must understand moisture in dry regions; enrich the soil diverse rotations, and cover crop mixes the importance of CA for food security with organic matter; and, if the mulch is is the most “natural” form of production for modern civilizations. Local farmer sufficiently dense, prevent the regrowth agriculture. The system exploits the diver- knowledge, innovative farmers, research of weeds. Diversified cropping patterns sity and synergy of living organisms that support, farmer-run associations, and composed of at least three species includ- shape each particular ecosystem with soil policy support are all necessary elements ing at least one legume are suggested. To C as the primary energy source. When soil to iteratively improve designs and equip- Copyright © 2015 Soil and Water Conservation Society. All rights reserved. incorporate more diversity, some farmers is not tilled, beneficial changes include ment for particular regions and soil types Journal of Soil and Water Conservation are using 10 to 12 species in cover crop an increase in soil life, increases in soil C in global adoption of CA. The many mixes (usually after small grain). While content and a change in the way nutri- farmers using CA principles and con- these three main principles are general in ents cycle in the soil. Churning the soil cepts globally can’t all be wrong (Kassam their application, specific differences in can release significant amounts of car- et al. 2014b). each principle need to be defined clearly bon dioxide (CO2) into the atmosphere to avoid confusion. The no-till system (Reicosky and Lindstrom 1993; Ellert and ACKNOWLEDGEMENTS employed in CA is not to be confused Janzen 1999; Reicosky and Archer 2007). The author would like to acknowledge helpful sug- with other forms of CT that substantially Without tillage, there are more environ- gestions and discussions with Rolf Derpsch, Dan disturb the soil surface. The success of the mental benefits accrued with fewer input Towery, Clark Gantzer, and several other scientists CA system concepts rely on and benefit costs over time. Many farmers are finding and conservation agriculture farmers. from the interactive synergies between the the hand-in-hand environmental and eco- 70(5):103A-108A biological, physical, and chemical proper- nomic benefits of this systems approach REFERENCES ties and processes in the soil that enhance for food security. Baker C.J, K.E. Saxton, and W.R. Ritchie. 2002. C management. Farmers using CA prin- Conservation agriculture is also climate- No-Tillage Seeding: Science and Practice. 2nd ciples and concepts globally are cultivating smart agriculture, making the transition ed. Oxford, UK: CAB International. more than 1.55 × 108 ha (3.83 × 108 ac; to farming better suited to the impacts of Baker, C.J., K.E. Saxton, W.R. Ritchie, W.C.T. www.swcs.org Kassam et al. 2014b). climate extremes that jeopardize food secu- Chamen, D.C. Reicosky, M.F.S. Ribeiro, S.E. True conservation is more about plant rity (Rosenzwieg et al. 2002). We can no Justice, and P.R. Hobbs. 2006. 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