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Introduction
"Conservation Agriculture" is a
generic term to replace the widespread use of "conservation tillage" to
describe farmer’s adoption of new tillage/seeding systems. Agricultural
production technologies that are geared towards resource conservation
involve more than tillage as seems to be implied by the use of
"conservation tillage". The Food & Agriculture Organization (FAO) have
suggested that a definition for conservation agriculture be:
"Involving a process to maximize ground cover, by retention of crop
residues, and to reduce tillage to the absolute minimum, while
exploiting the use of proper crop rotations and rational application of
inputs (fertilizers and pesticides) to achieve a sustainable and
profitable production strategy for a defined production
system."
Given the importance of integrating residue management
with crop rotation and production inputs, this FAO definition appears to
best capture the systems approach that is critical to sustainable
production systems. Crop residues alone do not make a sustainable
production system, but rather can be seen as the mortar that holds the
building blocks together. Any extensive farming system that does not
include the retention of crop residues is unlikely to be sustainable over
the long term.
It has been suggested that sustainable agricultural
systems must meet a number of criteria that increased diversification can
help to achieve. A sustainable cropping system must incorporate several
aspects: (a) productivity (maintaining or enhancing production), (b)
security (by reducing the level of production risk), (c) protection
(through the stewardship of natural resources), (d) viability (by ensuring
long-term economic survival) and (e) acceptability (adoption of farming
principles and practices which agree with the values within both the
agricultural sector and society at large) (Blade et al. 2002).
Conservation agriculture and diversified cropping are two building
blocks that are imperative in achieving sustainable cropping systems. A
third component, but equally important is in the understanding of the
interactions of man-made technologies and Natures resources - Integrated
Crop Management (ICM).
'Single' versus 'Multiple'
tools
Stressing diversity in crop management practices is more
challenging than stressing single tools. Producer needs for crop
management solutions are often so urgent that "quick-fix" solutions seem
imperative. In response, research and extension personnel have often
stressed single tools as opposed to packages of tools in entire cropping
systems. Single tools are easily recommended as the period of
decision-making in space and time occurs over only a few weeks in one
growing season. However, crop management problems are the result of
long-term decision-making process where all biological participants in the
ecosystem find their own niche in response to decisions made
previously.
Crop residues are critical for nutrient management,
microbial biodiversity, and soil and crop health. Crop residues increase
the biological life in soils and contribute to long-term sustainability
that provides nutrients (Soon and Clayton 2002), biological diversity
(Lupwayi et al. 1998, 1999), and disease control (Kelly Turkington,
personal communication). The ability of a soil to rebound from the process
of degradation is influenced by both the amount of degradation and the
restorative process. Crop residues are an important component of soil
restorative management, and for the most part have a long-term positive
impact on soil quality. Crop residues also make it possible to manipulate
crop management systems with multiple tools. Including genetic diversity
and rotational diversity can also help mitigate serious disease problems
that a single approach lacks (Turkington et al. 2000). Both direct seeding
and crop diversification contribute to the quantity and quality of
residues that impact the defined production system.
Fertilizer is
a major input into crop management and the methods employed to apply
fertilizer can impact yield and quality under both conventional tillage
and direct seeding (Grant et al. 2001). Often decisions regarding
fertilizer inputs are made in isolation of other management decisions and
neglect the impact it may have on disease, weeds and insects (Blackshaw et
al. 2000b). This neglect eliminates the opportunity for integrated pest
management. Applying N fertilizer and choosing field pea inoculation
formulations, without considering the potential environmental stresses,
may result in poor N2 fixation, poor crop health and future potential
problems for other crops (Clayton et al. 2004a, 2004b). In contrast,
understanding the potential problems and the interactive nature of
technologies, field pea health, contributions of N2 fixation, and benefits
to succeeding crops can be maximized. These examples of interactive
effects of fertilizer with other technologies demonstrate the importance
of understanding the complex system called a farm.
Herbicides,
fungicides or insecticides are effective in controlling or suppressing
pests and are one of the largest ‘single tool’ inputs into crop management
on a yearly basis. Increased seeding rate can aid in suppression of weeds
(Blackshaw et al. 2000a; Harker et al. 2003b; O’Donovan et al. 2000;
O’Donovan et al. 2001) but could be even more effective against weeds when
combined with an additional optimal factor such as a competitive cultivar
(Harker et al. 2003b; O’Donovan et al. 2000) or decreased row space
(Blackshaw et al. 2000a). Such practices may allow the use of lower rates
of pesticides or a reduced number of pesticide applications (Blackshaw et
al. 2000a, Harker et al. 2003b; O’Donovan et al. 2001). In a canola study,
combining a competitive cultivar, high seeding rate, and early weed
removal led to a 41% yield increase compared to the combination of a weak
cultivar (less competitive), low seeding rate and a later recommended
application time of weed removal (Harker et al. 2003b).
However,
early weed removal causes greater root maggot damage in canola (Dosdall et
al. 2003). In the case of root maggots and weeds, pressure to minimize
herbicide and insecticide use may drive the broader adoption of cultural
control strategies known to reduce infestations of these pests. Of
particular interest are practices that are effective against both pests or
at least effective against one without the affecting the other. It is not
always easy to make pest management strategies
compatible.
Operational diversity is another method to manage
potential future pest problems or environmental stresses. Changing seeding
dates of crops provides diversity in crop emergence dates and impacts
development stages of crops such as dormant seeded canola (Clayton et al.
2004) or winter cereals (Brian Beres, personal communication). Changing
harvest dates also reduces the potential problems created by the same
year-after-year harvest dates (Harker et al. 2003a). Combining operational
diversity strategies with other agronomic practices increases the ability
to plan and problem-solve in space and time.
Technologies and
information require "stacking" or "pyramiding" into packages that combine
several strategies for superior crop health that help the plant defend
itself against weeds, disease and insects. Beck (2002) reminds us that
‘successful crop production, regardless of the methods used, is a careful
piecing together of numerous components into a system. Simply replacing
one component with another is seldom successful’. Focusing on crop health
and competitiveness will lead producers to rely on packages of tools which
include such things as sanitation, low disturbance seeding (maintaining
crop residues), higher seeding rates, row spacing, optimum fertilizer
placement, and diverse crop rotations.
The complications of applying
biological and knowledge-intensive management versus the simple
application of problem-solving tools (pesticides, fertilizers) can be
intellectually intimidating. A higher degree of knowledge is required for
the successful integration of biological inputs, since they are ‘living’,
more diverse, or less specific, than single compounds and formulation of
compounds (see Figure below). But the most economic and environmentally
sustainable systems are likely to include a combination of biological and
technological inputs, pieced appropriately to solve crop management
problems.
References
- Blackshaw, R.E., Molnar, L.J., Muendel, H.-H. Saindon, G., and Li,
X. 2000a. Integration of cropping practices and herbicides improves weed
management in dry bean (Phaseolus vulgaris). Weed Technol.
14:327-336.
- Blackshaw, R.E., G. Semach, G., Li, X., O’Donovan, J.T. and Harker,
K.N. 2000b. Tillage, fertilizer and glyphosate timing effects on foxtail
barley (Hordeum jubatum) management in wheat. Can. J. Plant Sci.
80:655-660.
- Blade, S.F., G.W. Clayton, and D.J. Lyon. 2002. Introduction. Agron.
J. 94: 173-174.
- Clayton, G.W., Rice, W.A., Lupwayi, N.Z., Johnston, A.M., Lafond,
G.P., Grant, C.A. and Walley, F. 2004a. Inoculant formulation and
fertilizer nitrogen effects on field pea: Nodulation, nitrogen fixation
and nitrogen partitioning. Can. J. Plant Sci. 84: (January).
- Clayton, G.W., Rice, W.A., Lupwayi, N.Z., Johnston, A.M., Lafond,
G.P., Grant, C.A. and Walley, F. 2004b. Inoculant formulation and
fertilizer nitrogen effects on field pea: Crop yield and quality. Can.
J. Plant Sci. 84: (January).
- Clayton, G. W., Harker, K. N., O’Donovan, J. T., Blackshaw, R. E.,
Dosdall, L. M., Stevenson, F. C. and Ferguson, T. 2004c Fall and spring
seeding date effects on herbicide-tolerant canola (Brassica napus
L.) cultivars. Can. J. Plant Sci. 84: (In Press).
- Dosdall, L. M., G. W. Clayton, K. N. Harker, J.T. O’Donovan and F.
C. Stevenson. 2003. Weed control and root maggots: making pest
management strategies compatible. Weed Sci. 51:576-585.
- Grant, C.A., K.R. Brown, G.Z. Racz, and L.D. Bailey. 2001. Influence
of source, timing and placement of nitrogen on grain yield and nitrogen
removal of Sceptre durum wheat under reduced and conventional tillage
management. Can. J. Plant Sci. 81: 17-27.
- Harker, K. N., K. J. Kirkland, V. S. Baron, and G. W. Clayton.
2003a. Early-harvest barley (Hordeum vulgare) silage reduces wild
oat (Avena fatua) densities under zero tillage. Weed Technol.
17:102-110.
- Harker, K. N., G. W. Clayton, R. E. Blackshaw, J. T. O'Donovan and
F. C. Stevenson. 2003b. Seeding rate, herbicide timing and competitive
hybrids contribute to integrated weed management in canola (Brassica
napus). Can. J. Plant Sci. 83: 433-440.
- Lupwayi, N.Z., W.A. Rice and G.W. Clayton. 1998. Soil microbial
diversity and community structure under wheat as influenced by tillage
and crop rotation. Soil Biol. Biochem. 30:1733-1741.
- Lupwayi, N.Z., W.A. Rice and G.W. Clayton. 1999. Soil microbial
biomass and carbon dioxide flux under wheat as influenced by tillage and
crop rotation. Can. J. Soil Sci. 79:273-280.
- O’Donovan, J.T., Harker, K.N., Clayton, G.W and Hall. L.M. 2000.
Wild oat (Avena fatua) interference in barley (Hordeum
vulgare) is influenced by barley variety and seeding rate. Weed
Technol. 14: 624-629.
- O’Donovan, J.T., K.N. Harker, G.W. Clayton, D. Robinson, J.C.
Newman, and L. M. Hall. 2001. Barley seeding rate influences the effects
of variable herbicide rates on wild oat (Avena fatua). Weed Sci.
49: 746-754.
- Soon, Y.K. and G.W. Clayton. 2002. Eight years of crop rotation and
tillage effects on crop production and N fertilizer use. Can. J. Soil
Sci. 82: 165-172.
- Turkington, T.K., G.W. Clayton, H. Klein-Gebbinck, and D.L. Woods.
2000. Residue decomposition and blackleg of canola: influence of tillage
practices. Can. J. Plant Pathol. 22:150-154.
George
W. Clayton1, K. Neil
Harker1, R.E.
Blackshaw2, J.T.
O’Donovan3, L.M.
Dosdall4, T.K.
Turkington1, and N.Z.
Lupwayi3
1 Agriculture & Agri-Food Canada,
Lacombe Research Centre, 6000 C&E Trail, Lacombe, AB, T4L 1W1,
claytong@agr.gc.ca, harkerk@agr.gc.ca, turkingtonk@agr.gc.ca
2 Agriculture & Agri-Food Canada,
Lethbridge Research Centre, 6000 C&E Trail, Lethbridge, AB, 5403 - 1
Avenue South, PO Box 3000, Lethbridge AB T1J 4B1, blackshaw@agr.gc.ca
3 Agriculture & Agri-Food Canada,
Beaverlodge Research Farm, PO Box 29, Beaverlodge, AB, T0C 0C0,
O’Donovanj@agr.gc.ca, lupwayin@agr.gc.ca
4 AAFRD and Dep. of Agricultural, Food
and Nutritional Science, 4-10 Agriculture/Forestry Centre, Univ. of
Alberta, Edmonton, AB, Canada T6G 2P5, lloyd.dosdall@ualberta.ca |
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