TILLAGE INTENSITY, CROP ROTATION, AND FERTILIZER TECHNOLOGY FOR
SUSTAINABLE WHEAT PRODUCTION … NORTH AMERICAN EXPERIENCE
Roberts, T.L. and Johnston, A.M.
Potash & Phosphate Institute/Potash & Phosphate Institute of Canada
email: troberts@ppi-ppic.org
Summary
Approximately 95 million hectares (M ha) of the world’s cropland is under no-till; over 40% of
that area is in North America. Farmers in the Canadian prairies and the northern Great Plains pioneered
wheat production in reduced tillage systems when they began experimenting with no-till in the early
1970s. Today no-till, or direct-seeding, is used on about a third of the wheat farms in the U.S. and at
least half the wheat area in Canada. Most wheat growers using no-till seeding systems tend to diversify
their cropping rotations to maximize production efficiency. Proper understanding of nutrient behavior
in soil is necessary for appropriate fertilizer management in reduced tillage systems. Mobile nutrients
like nitrogen (N) and sulfur (S) are not impacted by a lack of soil mixing to the extent that phosphorus
(P) and potassium (K) are. Both P and K can become concentrated near the soil surface. This paper
will examine the behavior of soil nutrients in the absence of tillage and the resulting implications for
fertilizer management.
Introduction
North America leads the world in no-till crop production. No-till area in the U.S. is currently about
25 M ha and Canada has 13 M ha, together accounting for 41% of the 95 M ha worldwide (Table 1).
North America is also one of the world’s largest producers and exporters of wheat (FAO, 2005). The
U.S. is the world’s third largest producer and leading exporter, producing annually an average of about
60 billion metric tons (t) and exporting about 30 billion t. Canada ranks sixth in production with a
yearly average of 26 billion t and third in exports at almost 18 billion t.
The northern Great Plains has a total area of about 125 M ha, with some 52 M ha in crop
production (Padbury et al., 2002). Wheat (Triticum aestivum L.) is the dominant crop grown in the
region, followed by barley (Hordeum valgare L.) and oats (Avena sativa L.) as cereal grains. Corn
(Zea mays L.) is a dominant crop only in the southern regions where climatic conditions allow its
production. Canola (Brassica species) is the foremost oilseed crop in the region, grown mainly on the
Canadian prairies. Grain legumes (dry pea [Pisum sativum L.] and lentil [Lens culinaris L.]) are
growing in interest as a crop diversification option, but still only represent a very small proportion of
the cropping mix.
Environmental conditions on the northern Great Plains are described as severe by most, given the
cold winters and hot summers. However, the greatest limiting factor to production is likely the amount
and distribution of precipitation. Annual precipitation ranges mostly from 300 to 500 mm, with 165 to
300 mm falling during the April to July growing season (Padbury et al., 2002). The frost-free season
ranges from 83 to 157 days, representing a major diversity in crop production potential. The soils in
much of the northern Great Plains are frozen for 4 to 6 months of each year, minimizing microbial
activity, nutrient release and crop residue decomposition.
Farmers in the Canadian prairies and the northern Great Plains pioneered wheat production in
reduced tillage systems when they began experimenting with no-till in the early 1970s. Today no-till,
or direct-seeding (i.e. no tillage prior to seeding and minimum tillage at seeding), is used on about a
third of the wheat farms in the U.S. and at least half the wheat area in Canada. Most wheat growers
using no-till or direct-seeding systems tend to diversify their cropping rotations to maximize
production efficiency.
Erosion control is one of the main driving forces in the adoption of no-till in much of the world.
While erosion control is also important in the northern Great Plains wheat growing region, no-till
adoption was also driven by the need to improve moisture use efficiency (Brandt, 1992; Lafond et al.,
1992; Peterson et al., 2001). The semiarid climate of the Canadian prairies is ideal for producing high
protein wheat, but the region’s moisture limitations have made no-till cropping systems especially
attractive and economical (Zentner et al., 2002). Almost all of Canada’s wheat production is in the
Canadian prairies.
The Canadian prairies have about 30 M ha of cultivated land, which can be divided into five main
climatic/soil zones (Fig.1). The Brown soil zone has about 21% of the cultivated land, the Dark Brown
zone 22%, and the remainder in the more humid Black and Gray soil zones. Mean annual precipitation
ranges from about 300 to 400 mm in the Brown and Dark Brown soil zones to 425 to 475 mm in the
Black and Gray zones.
Spring wheat is the principal crop in all soil zones. Producers have historically selected rotations
that included high proportions of wheat and summerfallow, but fallow has been declining steadily
since the mid 1970s (Campbell et al., 1990; 2002) while the area under no-till and reduced tillage has
been increasing (Fig 2). Fallow frequency ranged from once every two years in the Brown soil zone to
one of four years in the Black soil zone, in direct relation with moisture availability. However, with the
better moisture retention with a no-till cropping system, growers have been able to greatly diversify
their rotations and increase cropping intensity (Table 2). Growers can now incorporate cereals (spring
and winter wheat, durum wheat, barley), oilseeds (canola, flax, mustard, sunflower), pulse crops (field
peas, lentils, chick peas), and forages into their rotations. Wheat still dominates in the rotation, but the
improved water conservation from no-till gives growers greater flexibility in their cropping systems in
any given year and oilseeds and pulse crops are now routinely part of a wheat based rotation (Miller et
al., 2001; Campbell et al., 2002; Miller et al., 2002; Johnston et al., 2002).
Soil Changes Related to Reduced Tillage
Tillage accelerates the natural processes of soil degradation; erosion, salinization, and acidification
rates increase, while the amount and quality of organic matter decreases. Soil organic matter breaks
down faster with frequent tillage, often resulting in a loss of plant nutrients. Regular tillage can also
break down soil structure and tilth, which reduces moisture-holding capacity and water infiltration
rates (Malhi et al., 2001).
When tillage is reduced, greater crop residues accumulate on the soil surface minimizing wind and
water erosion and improving the quality of the soil. Crop residues on the soil surface increase water
infiltration and reduce evaporation losses, reduce nutrient losses through erosion, and also lower the
surface temperature. Cooler soil temperatures will slow nutrient release from soil organic matter,
reduce diffusion of nutrients to the plant roots, and can affect root growth. In the absence of frequent
tillage, mineralization is slowed and the release of plant nutrients declines, making fertilization more
important in producing higher yields.
When crop residues accumulate in and on the soil surface because of less tillage, readilydecomposable plant residues and the active fraction of the soil organic matter eventually increase.
Initially, when no-till is first adopted the increased carbon (C) from the crop residues causes
immobilization of soil N as decomposing microorganisms use soil N to maintain their C:N ratios
during the decomposition process. With time the turn-over, or breakdown, of soil organic matter
reaches a new equilibrium and the pool of potentially mineralizeable N increases resulting in more
plant-available nitrate (NO3)-N and ammonium (NH4)-N. This transition period may last several years,
during which band placement of nutrients below the residue-covered surfaces becomes very important.
Most plant-available N in the soil is in the water-soluble NO3 form, which means it can leach and
moves throughout the soil profile with moisture. Sulfate (SO4)-S is also water-soluble and can move
within the soil profile, although under acidic soil conditions some SO4 can be also adsorbed to soil
colloids. Soil P and K tend to be immobile in the soil because of their reaction with calcium (Ca),
magnesium (Mg) and other soil minerals, and/or soil charge (cation exchange capacity [CEC]).
Without tillage and soil mixing, immobile nutrients may accumulate at the soil’s surface (0-5 cm). An
understanding of how nutrients move and react in the soil is necessary for proper fertilizer
management in reduced tillage systems.
Soil pH may decline as soil C (i.e. organic matter) levels increase under reduced tillage systems.
Changes will be proportional to the changes in organic matter and the initial pH of the soil. For
example, a 26% increase in soil C content was accompanied by a decline of 0.5 pH units in a gray soil
in western Canada after 10 years of no-till management (Arshad et al., 1990). Soil pH impacts nutrient
availability of P and some micronutrients.
Nutrient stratification is an important concern in the management of P and K in zero-till systems.
These immobile nutrients tend to accumulate in the soil surface at the depth of application. This is
illustrated with the data in Figure 3 from a Black, alkaline soil in Manitoba. Soil samples were taken
at the end of a 4-year study where P was banded (58 kg P2O5/ha) and K was broadcast (120 kg
K2O/ha). The lack of soil mixing during the 4 years caused P and K to accumulate where they were
originally placed.
Similar observations were made in a Brown soil in Saskatchewan. Selles et al. (1999) found that
after 12 years, converting from conventional till wheat-fallow to no-till continuous wheat resulted in an
accumulation of plant-available P in the upper 0-1 cm of surface soil. However, this was not the case
for no-till fallow wheat or conventional till continuous wheat. This specific treatment change was
attributed to the accumulation of surface residue and lack of decomposition in no-till. The increased
concentration of P at the soil surface did not result in greater P uptake by the wheat, but this was
probably because starter P was used at seeding and P release from organic matter was slow due to cool
soil temperatures in spring.
When soil conditions are dry, nutrients near the surface may be positionally unavailable for plant
uptake. This can be a common problem in prairie soils where precipitation is limited and soils are low
in P. However, it can easily be corrected by the use of starter fertilizer placed in the seed row.
Although N and S are mobile in the soil, tillage can also impact their distribution within the soil
profile. A study in Manitoba on a fine sandy loam found that NO3-N was higher in no-till than
conventional till in the 0-7.5 cm depth, presumably due to release from organic residues retained near
the soil surface and retention of residual N from fertilizer application under the dry conditions of the
study. Similar results were found in the surface 2.5 cm in a silty clay soil. Nitrate-N also accumulated
in the 60-120 cm depth in both tillage systems and soils. Other researchers in the Canadian prairies
have reported no effect of tillage system on soil NO3-N and SO4-S to a depth of 60 cm (Malhi et al.,
1992).
Fertilizer Management
Fertilizer management with no-till seeding requires careful attention to fertilizer placement to
optimize fertilizer use efficiency by the crop (Johnston, 2002). Soil characteristics, climate, crop type,
and agronomic practices, including fertilizer application method impact the efficiency of nutrient use.
Nitrogen is the nutrient most commonly limiting crop production world wide, followed by P and K.
Broadcasting N onto the residue covered surface is not the most efficient method of application
because of the potential for immobilization by surface residues and volatilization losses of N (Malhi
and Nyborg, 1992). In-soil band placement of N is usually the most effective means of minimizing
immobilization of N in no-till crops, but application of all the crop’s fertilizer requirements at seeding
can be challenging. Similarly, the application of P and K in bands either with, or close to the seed
minimizes tie-up by the soil and increases early season uptake by the crop, especially when applied as
starter fertilizer.
Figure 4 illustrates the effectiveness of starter P over a 31-year period in southern Saskatchewan in
a fallow-wheat-wheat rotation. Phosphorus application (15 kg P2O5/ha) produced on average 342 kg/ha
more grain for wheat grown on fallow and 197 kg/ha more grain for wheat grown on stubble. The
yield variability over the years was closely related to spring weather conditions and occurred although
soil test P had doubled over the 31 year period (Fig. 5). Greatest P response occurred when the soils
were cool and moist in the spring. Root growth and P movement in soil and uptake by plants is
hindered under low soil temperatures.
Although all the P requirements for wheat can be safely applied in the seed row as a starter, that is
not the case for high rates of N or K. Placement of high amounts of these nutrients directly with the
seed often causes reduced germination and delayed emergence resulting in poor stands and yield loss.
General recommendations used to suggest that no more than 45 kg/ha of N as ammonium nitrate or 2228 kg/ha of urea N could safely be applied with the seed. These recommendations were appropriate
for seeding equipment which placed the seed and fertilizer in close contact, but are not appropriate for
seeding equipment which causes some scatter between seed and fertilizer (pneumatic or airseeder), or
which can precisely place fertilizer away from the seed.
Many factors influence how much fertilizer can be safely applied with the seed. These include:
row spacing, seed bed utilization (SBU), soil texture, soil moisture, soil variability, fertilizer
placement, seed furrow opener, fertilizer source, and crop. The amount of fertilizer that can safely be
applied in the seed row decreases as row spacing increases. With wider rows, at a given rate per
hectare the fertilizer is more concentrated and is in greater contact with the seed. This is more of a
concern with N than with P. Research in Saskatchewan and Manitoba have shown that direct-seeded
wheat produced similar yields for row spacing ranging from 10 to 30 cm and that higher concentrations
of seed-placed P in wider rows had no effect on yield (Lafond et al., 1996).
Seed bed utilization is a measure of the amount of soil used for applying fertilizer (Roberts and
Harapiak, 1997). It is calculated as follows:
width of seedrow
X 100
row spacing
Heavier textured soils tolerate more seed row N because the increased cation exchange and water
holding capacity reduce ammonia toxicity, a major cause of germination and seedling damage.
Saskatchewan guidelines for the amount of urea N that can safely be applied with the seed, assuming
good to excellent seedbed moisture, are shown in Table 3. Application rates for ammonium can be
increased by about 25 %. Ammonium nitrate is less damaging to the seed than urea. It has a higher
salt index than urea, but does not add to ammonia toxicity. Higher rates of N may be tolerated if CEC
is high and seedbed moisture is excellent. Guidelines in North Dakota suggest that maximum seed row
N can range from 67 to 112 kg/ha when using an air seeder (60 to 100 % SBU) in a heavy textured
soil.
Many growers on the northern Great Plains have adopted the use of specialty seeding equipment
that places fertilizer in a separate band from seed to avoid seed germination and emergence problems.
Most commonly used are sidebanding openers mounted on pneumatic air drills, which provide a
fertilizer band that is usually 3-4 cm to the side and 4-5 cm below the seed row. Results from field
trial evaluation of these openers indicates that they all perform very well, as long as they are properly
adjusted for the seeding implement shank angle and the soil conditions (Johnston et al., 2001). Both
dry (urea) and gaseous N (anhydrous ammonia) sources, the two main N fertilizer forms used by the
region’s farmers, have been used when no-till seeding (Johnston et al., 1997). Using anhydrous
ammonia is more common in the higher moisture regions, where N rates required to optimize wheat
yields are higher.
% SBU 
Sulfur is the third most deficient nutrient in northern Great Plains, following N and P. It is not only
important for optimizing yields, but S is also an important component of several amino acids and
therefore affects the quality of bread wheat. Sulfur deficiencies are estimated to cover approximately
30% of the cultivated acreage in the Canadian Prairies and S soil testing is often unreliable in
predicting S status of a field (Grant et al., 2004).
Conventional soil testing that measures soluble SO4-S, the form of S available to plants, is
problematic because of the inherent variability of SO4 in the field and the variability of mineralization
of organic S, which usually accounts for 95% of the total S in the soil. Soil testing for S is most
reliable at predicting non-responsive soils that contain high amounts of S.
Sulfur is normally applied as elemental S or in the SO4 form. Elemental S must be oxidized by
microbial processes before being used by plants. The rate of conversion is dependent on characteristics
that enhance microbial activity (e.g. temperature, moisture, aeration, and pH). Oxidation rate generally
increases with increasing soil temperature and decreases with very low or very high moisture. Particle
size of the elemental S is also important; the smaller the particle size the faster the oxidation.
Dispersion of the S particles is also an important factor in increasing the rate of oxidation.
Application of elemental S in the spring at or near planting is not recommended for annual crops,
because the oxidation rate is too slow to meet the crop’s S requirements. Mixtures of bentonite and
elemental S are available that are intended to increase the dispersion of the S particles, thus increasing
the oxidation and release of SO4.
Compared to oilseeds, wheat is generally considered to have a low metabolic demand for S,
however yield increases to applied S fertilizers can be dramatic. Doyle and Cowell (1993) reviewed
studies from field experiments conducted on S-deficient soils in the more humid regions of the
Canadian prairies and reported yield increases ranging from 10 to 90% on soils that had never been
fertilized with S and 8 to 60% on soils that had a history of S fertilization (Table 4).
Sulfur fertilization is usually most effective when applied with adequate amounts of other nutrients.
For example, the application of 22 kg S/ha in a Gray soil increased wheat yields by 10% relative to the
control compared to a 30% increase when applied with N and P (Table 5). Applying N and P without
S resulted in a 7% yield increase. Whether with S or other nutrients, balanced fertilization is critical for
the production of wheat.
Nutrients must be applied in adequate amounts and in balanced proportions according to crop
needs and soil availability. Table 6 compares yields of fallow wheat in a fallow-wheat rotation with a
3-year fallow-wheat-wheat rotation and continuous wheat in a Dark Brown soil in southern Alberta
fertilized with low rates of N and P (Campbell et al., 1990). Highest wheat yields were obtained in the
wheat grown on fallow in the fallow-wheat rotation and when both N and P were applied. While
yields declined in the wheat grown on stubble, in all cases highest yields occurred only when both N
and P were applied together.
In the above example, K was not required to balance crop nutrition because the soils in southern
Alberta are rich in plant available K. In fact, most of the wheat growing soils of the northern Great
Plains are well supplied with K and normally would not be expected to respond to K fertilization.
Additionally, most of the K taken up by wheat is contained in the straw and in direct seeding
operations where the straw is retained in the field, little K is exported with grain, further lessening the
need for supplemental K fertilization. Despite this, some high K soils in the northern Great Plains do
respond to fertilization with muriate of potash (KCl).
Wheat response to KCl fertilization in high K soils may be partially attributed to restricted K
diffusion to plant roots when soils are cool in the early spring, but also to the chloride (Cl) contained in
the potash. Numerous studies in the northern Great Plains have demonstrated that wheat responds to
Cl fertilization (e.g. Fixen, 1993; Lamond et al., 1999; Grant et al., 2001); however, magnitude and
frequency of the response varies with cultivar and is often related to disease pressure.
Concluding Comments
Understanding soil nutrient behavior and its implications for fertility management is important for
maximizing nutrient use efficiency and wheat production in no-till cropping systems. Soil testing is
one of the best available tools to estimate soil nutrient levels and to make appropriate fertilizer
recommendations. To be most effective, soil testing must be used appropriately and in such a way as to
recognize the natural variability that exists in fields. Intensive soil sampling and/or nutrient
management by soil zones utilizing GPS (global positioning systems) and GIS (geographic information
systems) to map and track soil testing data are useful tools that can assist farmers in the nutrient
management of their wheat.
References
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quality of soil organic matter. Soil Biol. Biochem. 22:595-599.
Brandt, S.A. 1992. Zero vs. conventional tillage and their effects on crop yield and soil moisture. Can.
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chloride fertilization. Better Crops 85(4):20-23.
Grant, C. A., Johnston, A. M., and Clayton, G. W. 2004. Sulphur fertilizer and tillage management of
canola and wheat in western Canada. Can. J. Plant Sci. 84: 453-462.
Henry, L., Harapiak, J., Ukrainetz, H., and Green, B. 1995. Revised guidelines for safe rates of
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Johnston, A.M., Lafond, G.P., Harapiak, J.T., and Head, W.K. 1997. No-till spring wheat and canola
response to side banded anhydrous ammonia at seeding. J. Prodn. Agric. 10: 452-458.
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winter wheat. Better Crops 83(4): 21-23.
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barley. Soil Tillage Res. 23, 193-197.
Malhi, S.S., McAndrew, D.W., and Carter, M.R. 1992. Effect of tillage and N fertilization of a
Solonetzic soil on barley production and some soil properties. Soil Tillage Res. 22:95-107.
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no-till cereal production in the Canadian Great Plains: a review. Soil and Till. Res. 60: 101-122.
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G.P., Schatz, B.G., Baltensperger, D.D., and Neill, K.E. 2002. Pulse Crop Adaptation in the
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Table 1. Extent of no-tillage adoption worldwide, 2004/05.
Country
No-till area, million ha
USA
25.3
Brazil
23.6
Argentina
16.0
Canada
13.4
Australia
9.0
Paraguay
1.7
Indo-Gangetic-Plains
1.9
Bolivia
0.6
South Africa
0.3
Spain
0.3
Venezuela
0.3
Uruguay
0.3
France
0.2
Chile
0.1
Colombia
0.1
China
0.1
Others (estimate)
1.5
Total
94.6
(J. Hassell, Conservation Technology Information Center, personal communication)
Table 2. Trends in cropping intensity in the Canadian prairies.
Average rotation length*
Soil zone
1976
1980
1985
1990
1995
Brown
1/1.1
1/1.1
1/1.3
1/1.3
1/1.3
Dark Brown
1/1.4
1/1.5
1/2.1
1/2.2
1/3
Black and Gray
1/2.2
1/2.6
1/4.9
1/4.9
1/6.7
*Interpret rotation 1/1.1 as one year fallow to 1.1 year in crop
(Campbell et al., 2002)
1998
1/1.6
1/4
1/10
Table 3. Approximate safe rates of urea N (kg/ha) that can be safely applied with wheat and other cereal grains.
Soil Texture
Light (sandy loam)
Medium (loam to clay loam)
Heavy (clay to heavy clay)
(Henry et al., 1995)
2.5 cm spread
(Disc or knife)
Row spacing, cm
15
23
30
SBU
17%
11%
8%
22
17
17
34
28
22
39
34
34
5 cm spread
(Spoon or hoe)
Row spacing, cm
15
23
30
SBU
33%
22%
17%
34
28
22
45
39
34
56
45
39
7.5 cm spread
(Sweep)
Row spacing, cm
15
23
30
SBU
50%
33%
25%
45
34
28
56
45
39
67
56
45
Table 4. Average yield response of wheat to S application in Alberta soils that have never received S fertilization
and soils that have received S continuously for 20 years.
Location
Control
Fertilized*
------------ kg/ha ------------
Yield increase,
%
No. of
trials
No previous S application
Gray Wooded Soils†
1422
1619
14
12
Breton‡
949
1830
93
20
U of A§
2482
2731
10
8
20-year history of S application
Breton‡ 1
774
1178
52
5
2
2059
2225
8
5
3
1690
2737
62
5
4
2523
3641
44
5
U of A§ 1
3379
3659
8
4
2
1999
2023
1
4
* S applied at 15 kg /ha as Na2SO4
† Average total S = 123 mg/kg; ‡ Average total S = 100 mg/kg; § Average total S = 670 mg/kg
(Doyle and Cowell 1993).
Table 5. Effect of N, P, and S fertilization on wheat yields in Alberta.
Treatment
N
P2O5
S
Wheat yield
-------------------- kg/ha -------------------1
0
0
0
2310
2
0
0
22
2550
3
18
22
0
2480
4
18
22
22
3020
(Doyle and Cowell 1993)
Table 6. Influence of N and P fertilization in wheat grown on fallow and stubble in a Dark Brown soil in southern
Alberta.
Fertilizer, kg/ha
Rotation sequence, 13-yr mean yield, kg/ha
Wheat grown on fallow
Wheat grown on stubble
N
P
F-W
F-W-W
F-W-W
Continuous W
0
0
2775
2332
1203
1156
0
20
2802
2641
1176
1284
45
0
2722
2460
1519
1505
45
20
3031
2654
1908
1747
Letters in bold face represent the phase of the rotation the yield was determined.
(Campbell et al., 1990)
9.00
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
20
01
No-till area, M ha
Figure 1. Soil zones of the Canadian prairies.
Figure 2. No-till area in the Canadian prairies (B. McClinton, Saskatchewan Soil Conservation Association
personal communication).
1300
1200
60
Conventional Till
50
Zero Till
40
30
Potassium, mg/kg
Phosphorus, mg/kg
70
1100
Conventional Till
1000
Zero Till
900
800
700
600
20
500
Silty Clay Soil
10
400
0
Silty Clay Soil
300
0
5
10 15 20 25 30 35 40 45
Depth, cm.
0
5
10 15 20 25 30 35 40 45
Depth, cm.
Figure 3. Effect of zero and conventional tillage on distribution of P and K in a silty clay soil in Manitoba (adapted
from Grant and Bailey 1994).
Wheat on Stubble
Wheat on Fallow
1200
Yield increase, kg/ha
1000
800
600
400
200
0
-200
19661969197219751978198119841987199019931996199920022005
Figure 4. Yield increase in response to starter P application in a Saskatchewan fallow-wheat-wheat rotation, 19672004. (R.P. Zentner, Agriculture and Agri-Food Canada, personal communication).
F-W-W (N+P)
F-W-W (N)
60
Olsen P, kg/ha
50
40
30
20
10
0
1965
1975
1985
1995
2005
Figure 5. Influence of starter P fertilizer application on soil test P levels in the wheat phase of a fallow-wheat-wheat
rotation in Saskatchewan, 1967-2004 (R.P. Zentner, Agriculture and Agri-Food Canada, personal
communication).