Cynthia Grant, Agriculture and Agri-Food Canada, Brandon Research Centre, Brandon,... Email: Crop Management to Reduce N Fertilizer Use

Cynthia Grant, Agriculture and Agri-Food Canada, Brandon Research Centre, Brandon,... Email: Crop Management to Reduce N Fertilizer Use

Crop Management to Reduce N Fertilizer Use
Cynthia Grant, Agriculture and Agri-Food Canada, Brandon Research Centre, Brandon, MB R7A 5Y3
Email: [email protected]
Martin Entz, Dept. of Crop Science, University of Manitoba, Winnipeg, MB R3T 2N2
Email: [email protected]
Introduction
The current high nitrogen prices make it increasingly attractive for producers to reduce nitrogen inputs
and increase nitrogen use efficiency. However, an adequate nitrogen supply is still necessary for optimum
crop yield and quality. Most prairie soils do not supply enough N to produce maximum yields of canola
or cereal crops. Therefore, nitrogen fertilizer is generally required to optimize yield of non-legume crops.
Nitrogen management balances the needs of the crop for optimum economic yield and quality and the N
supply that the plant can access as needed. Nitrogen supply from the soil includes the residual soil N that
is present at seeding, the N released from mineralization over the growing season, and for legume crops,
N that is symbiotically fixed through the legume-rhizobium interaction. Nitrogen supply is reduced by
the losses of N that occur through the season. Nitrogen fertilization should make up the difference
between the demands of the plant and the supply from the soil.
There may be ways of adjusting the cropping system to reduce nitrogen requirements and improve the
economics of production. These include:
•
•
•
•
Producing crops with a low nitrogen demand
Growing your own nitrogen
Explore alternate nitrogen sources
Optimise efficiency of nitrogen fertilizer applications
Producing crops with low nitrogen demand
The amount of N needed to produce a crop depends on the yield potential and the nitrogen concentration
of the crop. High-yielding crops such as corn or barley remove more nitrogen than lower-yielding crops
such as flax (Table 1). Crops with high protein content, such as canola, remove more nitrogen than lower
protein crops. Crops such as flax that use relatively low amounts of nitrogen, may become relatively
more attractive as the price of nitrogen increases.
Table 1: Nutrient removal in harvested portion of common crops ( CFI 1998)
Harvested
Bushel
N
P2O5
Yield
Weight
Crop
Sp. Wheat
W. Wheat
Corn
Barley
Oat
Canola
Flax
---bu per acre-40
50
100
80
100
35
24
--lb per bu-60
60
56
48
32
50
56
K2O
S
-----------------------lb per acre-------------------------54-66
21-26
16-19
4-5
47-57
23-28
15-19
6-8
87-107
39-48
25-10
6-7
70-85
30-37
23-28
6-8
55-68
23-28
17-20
4-5
61-74
33-40
16-20
10-12
46-56
14-17
13-16
5-6
1
Growing your own nitrogen
Annual legumes, such as soybean, field pea, or lentil can symbiotically fix N in association with
Rhizobium sp. If properly inoculated, these crops do not require application of nitrogen fertilizer. As the
price of nitrogen fertilizer increases, the economic advantage from growing legume crops that can
produce their own nitrogen fertilizer increases.
Pulse crops can also increase the amount of available N for the following crop. With legume pulse crops,
such as soybean, field pea or lentils, where the seed is harvested and removed from the field, the amount
of N removed in the seed is generally similar to the amount of symbiotic N fixation. Despite this, N
requirements are generally reduced in crops following pulse crops, indicating that pulse crops increase the
available N for subsequent non-legume crops. Estimates of N contributions to following crops ranges
widely (less than 10 to greater than 70 lb/acre) and will depend on legume yield, management practices
and environmental conditions. Legume residues contain considerable amounts of N and have a relatively
low C:N residue, leading to more rapid release of N than lower N-containing cereal residues Work by
Sawatsky and Soper (1991) at the University of Manitoba indicated that up to 44% of N fixed by
legumes remained in the soil after roots were physically removed from the soil, and was presumably
present in irrecoverable root material, or lost from the plant root by sloughing and exudation. Some of
this fixed N remaining in the soil would become available for subsequent crops. Increased N availability
to crops following legumes may also be due to reduced immobilization, as legume crops generally
produce lower amounts of crop residue with a higher nitrogen concentration than do cereal crops.
Forage legumes also fix large amounts of nitrogen and a portion of that nitrogen will be release to the
following crop after forage termination. According to MAFRI, 5-year alfalfa stand can provide
considerable nitrogen for 2 following crops, and nitrogen benefits can last for up to 7 years. The
estimated nitrogen released after a forage stand depends on the timing of termination and the density of
legume in the stand.
Table 2: Estimated nitrogen supply after termination of alfalfa stands
Termination Time
N for following crop
Lb N/ac
90
Before July
70
July-August
45
Fall
30
Spring
Table 3: Adjustment of estimated nitrogen supply in table 2 for alfalfa stand density.
Alfalfa stand/sq foot
Portion of above credit available
>5
3-4
1-2
<1
Full credit
2/3 credit
1/3 credit
0 credit
If the legume crop is used as a green manure, considerable amounts of N can be supplied to the
succeeding crop as the legume residue decomposes. MAFRI (2001) suggests that a legume green manure
crop ploughed under at the blossom stage can provide more than 100 pounds of nitrogen per acre, while a
grass-legume mix turned under at the same stage can contribute 50-100 pounds of N per acre. However,
if the grass and legume is harvested and the residue turned, it will contribute less than 50 pounds of N per
acre.
2
Table 4: Some advantages and disadvantages of green manure crops
Pros
Cons
Produce nitrogen
Forgo a year of income
Organic status
Establishment is sometimes difficult
Possible weed suppression
Weed control may be a problem
Break disease cycles
May deplete water - lower yield of next crop
Increase soil organic matter
Erosion control
Improve soil structure
Reduce compaction
Reduced soil pH
A wide variety of legume crops can be used as green manures. Yellow sweet clover and alfalfa are the
most commonly used, but white clover, red clover, peas, Indian Head lentils, black medic and certain
vetches. In studies conducted by Bullied et al. (2002) in Winnipeg, a range of green manure crops were
effective in contributing nitrogen to the following wheat crop.
Total Grain N Uptak
(kg/ha)
100
1997
80
1998
60
40
20
0
w
llo
Fa
la
no
Ca
r
l
h
fa
m
ve
nti
etc
ee
fal
o
l
l
s
V
Le
r
A
dC
ng
Be
ro
Re
kli
Nit
c
i
Ch
Figure 1: Effect of Green Manures on Wheat Grain N after Green Manure Crops at Winnipeg (Bullied et
al. 2002)
When estimating nitrogen contribution from green manure, roughly 30 kg N/ha is produced for every
1000 kg DM/ha of legume. In Manitoba, legume GM crops can produce about 3000 to 4000 kg/ha, which
provides 90 to 120 kg N/ha. Of 120 kg N, about 60% becomes available over the following two years, or
about 50 kg N in year one after GM and 10 to 15 kg N/ha in year two. The remaining N is in SOM and
becomes available later.
A major disadvantage to the production of green manures is that production of a saleable crop is foregone
for a year. Use of relay-cropping or double–cropping can allow the production of both a legume green
manure crop and an annual cash crop in a single year.
In relay cropping (Figure 2), a legume crop, or relay crop, is seeded directly into the established first crop.
For example, alfalfa and red clover can be sown as relay crops into winter wheat and fall rye in the spring
after they are established (University of Manitoba 2004).
3
Figure 2: In relay cropping, an under-seeded legume crop fixes nitrogen through the growing season and
into the fall.
With double cropping, a legume crop is sown after the harvest of an early-maturing crop such as
winter wheat or fall rye. Both relay cropping and double cropping take advantage of the heat and
moisture available after the main crop is harvested but before a killing frost.
Figure 3: In double cropping, a legume crop seeded after the main crop is harvested fixes nitrogen until a
killing frost.
Relay or double cropping can be effective if moisture and heat are not limiting. Cereal and cover crops
can be planted at 100% recommended rates. For proper nitrogen fixation, legume cover crops must be
inoculated with proper bacteria to achieve N benefits
Application of composts and manures
Manures and composts are good sources of nitrogen for crop growth. The value of manure application
and the benefits of managing to conserve its nitrogen content increase as the price of nitrogen increases.
The nitrogen in manure is present as both inorganic and organic forms and so can provide both
immediately and slowly available N. In liquid hog manure, most of the N in is the inorganic form and
rapidly available for crop uptake. In contrast, in cattle manure, much of the N is in an organic form, which
is slowly released over time. The release of N from solid manure is highly variable and depends on the
environmental conditions, manure handling and the characteristics of the manure. For example, manure
containing a high proportion of straw will release N more slowly because of its high C:N ratio. It is
roughly estimated that about 25% of the organic nitrogen will be available to plants in the first year, with
4
the remainder becoming available during the next three years at a decreasing rate. Injection or rapid
incorporation of manures reduces nitrogen losses, allowing the greatest benefit from the nitrogen in the
manure.
Composted manure tends to mineralize more slowly and contains a lower portion of nitrogen than
uncomposted manure. About 50% of the nitrogen in the manure will be lost in the composting process, as
compared to about 25% with stockpiling of manure.
Remember the basics of nitrogen fertilizer management
As the price of nitrogen rises, it becomes using effective fertilizer management to optimise fertilizer use
efficiency become increasingly important. Effective fertilizer management in any cropping system deals
with four major factors:
1. Rate: Selected to optimize yield, but not lead to negative effects on crop or environmental
quality
2. Source: Suited to the time and method of application
3. Timing: Selected to ensure that adequate amounts of nutrient are available when required by
the crop, losses are minimized and operation is efficient in terms of time management
4. Placement: Placed where nutrients are available to the crop when the nutrient is required for
plant growth, losses are minimized, crop damage is avoided and nutrient use efficiency is
optimized.
Determining Nitrogen Application Rate
To be able to choose our N application rate, we need to estimate how much N the crop needs for optimum
economic yield and how much N will be available from the soil for the crop to use. Nitrogen supply will
include both the N in the soil at seeding and the N released during the growing season. With legume
crops, it also included N fixation. Fertilizer N rate should be enough to make up the difference between
the crop requirement and the soil supply, keeping in mind that N losses will occur from both the soil and
the fertilizer we add.
N fertilizer = Crop demand - N in soil - N released + N losses from soil and fertilizer
Crop Demand
Crop demand for N will depend on the type of crop produced as mentioned previously and on the yield
potential of the crop. The amount of N needed to produce a crop depends largely on the yield potential of
that crop. For example, a wheat crop needs about 2 to 3 lbs of N to produce a bushel of wheat, so a 60
bu/acre crop will need substantially more N than a 30 bu/acre crop. Crop N requirement can therefore be
estimated by selecting a reasonable target yield. In many areas, target yield is primarily determined by
the available moisture, including stored soil moisture and anticipated precipitation. However, target yield
will also be influenced by a wide range of factors including soil characteristics, target protein content,
management practices, crop rotation, length of growing season, and likelihood of weed, disease and insect
problems. Deficiency of nutrients other than N will reduce yield potential and should be corrected, so
that the target yield is based on yield restriction imposed by factors that can not be economically
controlled. Past experience will help in setting a reasonable target yield. Nitrogen supply should be
selected to support that yield and quality goal.
Soil Supply
Where an effective soil test is in place, soil testing is still the best tool to estimate available soil N.
However, considering input and removal of N from the soil system can improve the estimate of N supply
from the soil to fine-tune fertility recommendations.
5
Crop Removal in Preceding Year: Each bushel of wheat at 14% protein removes approximately 1.5 lb of
N from the system in the grain. With high crop yields in the preceding year, crop removal will likely
have depleted reserves of soil N, leading to a reduced supply of available N for the current crop. This is
particularly true if the crop also contained high protein content, which will increase N removal.
Cropping Intensity: Moving from cropping systems that include fallow to continuous cropping systems
will increase annualized crop yield and so total nutrient removal with continuous cropping will be
substantially higher than with a fallow cropping system. With increased nutrient removal, responses to
fertilizer applications become more likely. Therefore, in intensive cropping systems, N fertilization
becomes increasingly more important.
While crop removal of nutrients is increased by cropping intensification, the amount of organic residues
returned to the system is enhanced by more frequent cropping, which can increase the potential for
nutrient release from organic matter residues, particularly in fertilized systems. Nitrogen returned to the
system via crop residues from previous years of cropping serves to replenish the organic nutrient pool in
the soil. Historically, fallow systems have relied upon N mineralized from the soil organic matter to
provide N for the succeeding crop. Over time, insufficient crop residues were returned to the soil to
compensate for the loss in N supplying capacity of the soil due to fallowing. This, combined with the soil
erosion associated with fallowing, led to soil organic matter depletion and an overall decline in the
capacity of the soil to mineralize N. Therefore, although continuous cropping will reduce the amount of
residual mineral N in the soil, in the long-term it may increase the potential ability of a soil to supply N to
a crop via mineralization during the growing season. There is still some question as to how many years of
good management it will take before the potential for greater N mineralization will be reflected in situ.
Crop Rotation: A diversified crop rotation can increase yield potential, which will increase the crop
nutrient demand. However, crop rotations may also influence the supply of nutrients to the growing crop.
Crops differ substantially in the amount of N returned in the crop residue for use of subsequent crops,
since N supplied will depend on the amount of crop residue, primarily, and on the concentration of N in
the residue. Nitrogen concentration in the residue will determine the net balance between immobilization
and mineralization. Jay Goos of North Dakota State University suggested that if the N concentration in
the residue is below approximately 20-24 g N kg-1, immobilization will exceed mineralization and the
decomposing residues will tie up N rather than release it.
Over the long term, as decomposition proceeds, all residues will eventually release the minerals they hold.
The time required for this to occur will increase as the initial N concentration in the residue decreases and
the C/N ratio widens. In studies by Janzen and Kucey at Lethbridge, that N concentration of lentil, rape
and wheat residue had a dominating influence on rate of residue decomposition and nutrient release.
Increasing the N concentration of the residue by fertilization increased rate of residue decomposition.
Straw from a well-fertilized wheat crop will decompose more rapidly and release more N to the following
crop than will an N-deficient crop. Therefore, species and nutrient management of the preceding crop
will influence its nutrient content and the amount of nutrient it will release to the subsequent crop.
Placement of residues and method of termination of the crop will also influence N release. Soil
incorporation of residues reduces N loss by volatilization, enhances mineralization and increases the
short-term supply of plant-available N.
Past N management: Both residual soil N and the potential release of N from mineralization will be
influenced by long-term N management. Long-term crop production in the absence of adequate N
applications will reduce soil organic matter, potentially mineralizable N and residual soil N. In contrast,
long-term cropping with N applications designed to optimize crop yield potential, combined with return
of crop residue to the system, can slow the loss or possibly even lead to increases in soil organic matter
over time. Therefore, a long-term history of effective N management and good residue management will
6
N-Supplying Powe
(kg/ha/wk)
lead to a greater ability of the soil to supply N for crop growth. Application of high N organic
amendments such as manure or green manures will also increase the supply of N from the soil and reduce
the rate of N required for crop production.
60
50
F-W-(W)
40
F-W-(W) N+P
30
Cont (W)
20
Cont (W) N+P
GM-W-(W)
10
F-W-(W)-H-H-H
0
Crop Rotation
Figure 4: Effect of past management on N-supplying power of the soil (F=fallow; W=wheat; GM = green
manure; H=hay; N+P=nitrogen and phosphorus fertilizer). (Campbell et al. 1991).
Expected Efficiency of Fertilizer Application: The more efficiently N fertilizer is used by the crop, the
less N fertilizer is needed. Therefore, if the source, timing and placement package and the environmental
conditions combine to produce high N efficiency, rate of application can be reduced. In contrast, if a less
efficient management package is selected because of other management constraints on the farm, or to
improve operational efficiency in another area of the production package, the reduced efficiency can be
compensated for by increasing fertilizer rate.
Selecting nitrogen sources
Nitrogen fertilizer supplies N in the form of ammonium, nitrate, urea (which rapidly converts to
ammonium in the soil), or as a blend of these ions. Both nitrate and ammonium sources are subject to
immobilization losses. However, ammonium and nitrate sources differ in their susceptibility to losses by
volatilization, denitrification and leaching.
Ammonium and urea sources are more prone to volatilization losses than are nitrate sources. This is
because they convert to ammonia gas which can be lost to the environment. Therefore, these sources
should be applied where volatilization potential is low, or placed in a way that reduces volatilization
losses.
Nitrate sources are more prone to leaching and denitrification losses than are ammonium sources.
Therefore, under conditions where leaching or denitrification is likely, ammonium or urea sources are
preferable to nitrate sources. However, microorganisms in the soil convert ammonium to nitrate through
nitrification, with the rate of conversion increasing with optimal moisture conditions and increasing soil
temperature. So, over time, ammonium and urea will also become susceptible to losses as they change to
nitrate. Placing these fertilizers in a way to slow the conversion to nitrate will improve efficiency.
Nitrogen placement
Broadcast and surface applications: With surface applications, N can be lost by volatilization until it is
incorporated or moves into the soil with precipitation. If the N is in close contact with crop residues, it
may also be subject to immobilization as the residues decompose, since with high C:N ratio residues
microorganisms will use N from the soil or fertilizer as they break down the residue. Because of the high
potential for volatilization and immobilization losses, surface applications of N tend to be less efficient
7
than in-soil banded applications. Efficiency of surface applications tends to improve in higher rainfall
areas, since precipitation will move the fertilizer into the soil, reducing the risk of loss and of stranding at
the soil surface. Efficiency is lower on high pH soil, since high pH encourages the production of
ammonia gas.
As ammonium nitrate is no longer available as an N source in the prairies, urea ammonium nitrate (UAN)
is likely the preferable source for surface applications. Use of UAN may reduce volatilization losses,
since the nitrate is not subject to volatilization and the effect on pH in the reaction zone of the fertilizer is
not as great as with urea. Urea is particularly subject to volatilization losses if surface applied without
incorporation, since the concentration of ammonium released from urea is high. The presence of crop
residues at the soil surface may increase volatilization, since the residues contain the urease enzyme
which breaks down urea and makes it subject to loss as ammonia gas. The crop residue may also
increase immobilization, since the raw organic matter, with a high C:N ratio will tie up N as the residue
decomposes. Therefore, separation of the crop residue and the N, by placing the fertilizer below the
residue may be even more important under reduced as compared to conventional tillage.
These effects were shown in studies with durum, conducted on a clay loam and a fine sandy loam soil in
Manitoba (Table 2). Under conventional tillage, spring banded applications of urea produced similar
yields to broadcast urea. Under reduced tillage, the in-soil spring banded application produced higher
yields than the broadcast applications, in spite of the extra soil disturbance associated with the banding
action.
Table 5: Yield of durum grown under conventional tillage (CT) and zero tillage (ZT) with varying
placements of 55 kg N ha-1 as urea (1992-95) (Grant et al., 2001).
______________________________________________________________________________
Method of
Clay Loam
Fine Sandy Loam
Placement
CT
ZT
CT
ZT
------------------------bu per acre--------------------Fall Banded
44
30
43
42
Spring Banded
44
41
39
40
Dribble Banded
45
34
37
41
Broadcast1
45
33
41
38
Control
33
22
28
25
__________________________________________________________________________________
1. Broadcast without incorporation for reduced tillage and with incorporation for conventional tillage
Volatilization losses will be minimized by application of the fertilizer early in the growing season when
air and soil temperatures are cool. In conventional tillage systems, incorporation immediately after
application will minimize losses. In no-till systems or on perennial forages, where incorporation is not an
option, rainfall soon after application will wash the fertilizer into the soil, reducing losses. Use of urea
ammonium nitrate (UAN) dribble bands as post-seeding treatments up to the 4th leaf stage of the crop
may also produce good results.
Use of urease inhibitors such as Agrotain (NBPT) in the urea fertilizer can also reduce volatilization
losses. Urease inhibitors slow the conversion of urea to ammonium ions. This allows more time for the
urea to move into the soil before release of ammonium ions leads to a high risk of ammonia volatilization.
Also, with slower release of the ammonium ions, concentration of ammonia at the soil surface would be
reduced, which reduces the rate of volatilization. In studies where N volatilization over a two week
period was measured using polyfoam traps in tubes set in the field, volatilization was reduced to a far
greater extent by use of Agrotain than by application of 1.5 inches of water as irrigation treatments split at
8
day 4 and day 7 (Table 6). However, the benefit of this will depend on the cost of the product relative to
potential losses.
Table 6: Cumulative losses of N over a two week period from surface broadcast urea applications with
and without irrigation or Agrotain application (Rawluk, 2000)
N Volatilization (%)
Day 1
Day 2
Day 5
Day 8
Day 12
Day 14
No irrigation
0.23
1.13
12.97
25.80
30.22
31.45
No irrigation + Agrotain
0.08
0.24
1.92
4.22
7.58
11.07
Irrigation
0.30
0.77
8.06
14.07
14.98
15.25
Irrigation + Agrotain
0.05
0.16
0.90
2.37
2.90
3.37
In-soil banded or nested applications: By placing N fertilizers as bands or nests in the soil, problems
with volatilization are reduced substantially. Once in the soil, nitrogen is more readily lost from the
nitrate form than the ammonium form. This is because both ammonium and nitrate can be immobilized by
soil microorganisms, but nitrate is also subject to losses by denitrification and leaching. Therefore, in-soil
applications of N tend to be more efficient when a larger proportion of the N is in the
ammonia/ammonium form. With spring applications, where plant uptake will begin soon after
application, source of N may not be particularly important. But, if the fertilizer will be in the soil for an
extended period of time prior to plant uptake, use of ammonium or ammonium-producing sources may
improve fertilizer use efficiency.
Nitrogen timing
Fall banding is a popular timing of application in much of Manitoba. A fall banding operation allows for
spreading of the workload, by shifting the fertilization operation to late in the fall, rather than during
seeding in the spring. Fertilizer costs may also be lower in the fall as compared to the spring and there
may be other financial advantages to purchasing fertilizer in the fall. Soils in Manitoba are normally
frozen from mid-November to mid-March and losses of N from frozen soils will be minimal. In addition,
there is generally a relatively low risk of having a prolonged period with the combination of warm
temperatures and saturated conditions. However, with fall applications, fertilizer N will be subject to
losses from the time of application until the soil freezes in the fall and from spring thaw until plant
uptake. These losses are minimal if the soil is dry and well-drained, but can be substantial in wet, warm
soils. To minimize losses from denitrification and leaching, it is desirable to apply the fertilizer when
surface soil temperatures have cooled below about 5 to 10 C, so that reaction of the N in the soil will be
limited. The most efficient sources are generally ammonia or urea, rather than sources containing a
higher proportion of nitrate. Also, one would wish to maintain the fertilizer in the urea or
ammonia/ammonium form for as long as possible. Placing the fertilizer in a band reduces the contact
between the fertilizer and the soil microorganisms, reducing immobilization of both ammonium and
nitrate. Banding also slows the conversion of urea to ammonium and ammonium to nitrate, which can
reduce losses by denitrification and leaching. Applying the fertilizer as late as possible in the fall, when
soil temperatures are low, would also reduce losses of the N through microbiological activity.
In principle, N use by plants will be optimized and N losses minimized if N supply is closely matched
with N demand by the plant in timing as well as in rate. Synchrony between plant-available N in the
rooting zone and the crop uptake of N, in rate and timing, will minimise N losses prior to plant uptake.
Use of split applications, where N is applied in small increments frequently during the growing season
rather as than a single large application at the beginning of the season, can be used to more closely match
N supply with the period of maximum N demand (Power et al., 2000). With high value crops equipped
with drip irrigation systems, N may be added efficiently in the irrigation water to respond to crop
9
requirements (Neilsen et al., 2002), but split applications can also be applied with trickle and centre pivot
systems in lower-value irrigated crops. However, multiple applications of fertilizer may be impractical
for lower value crops in non-irrigated broad area agriculture, due to the cost associated with the extra
applications. In drier regions where rainfall is erratic, in-crop applications may be stranded on the soil
surface and not be taken up effectively by the crop. Foliar fertilization may be effective in applying
relatively small amounts of N, for example for protein enhancement, but may not be able to supply the
bulk of N to support crop yield. Surface applications may also be lost by volatilization or immobilized on
surface residues, especially of urea sources are used
Fine-Tune the cropping system
For a crop to take advantage of available nitrogen, the overall cropping system must be optimised.
Tillage management, crop genetics, pest control, water management and soil tilth must all be managed
effectively so that the crop is able to convert the N supplied into usable yield with the greatest efficiency.
As the yield potential of the crop increases due to factors other than N input, such as better use of water,
balanced fertility, higher yielding cultivars, disease control, timeliness of operations or improvements in
soil structure, the yield per kg of N will improved. All resources, including land, water and N fertilizer,
will be used more effectively if yield potential is optimised. Therefore, as N costs go up, it is critical that
all aspects of crop management on the farm be fine-tuned to ensure that each dollar spend on N fertilizer
is used as efficiently as possible.
10
References
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sequential wheat and barley crops from single-year alfalfa, berseem and red clover, chickling
vetch and lentil. Can. J. Plant Sci. 82: 53–65.
Campbell, C.A., G. P. Lafond, A. J. Leyshon, R. P. Zentner, and H. H. Janzen. 1991. Effect of cropping
practices on the initial potential rate of N mineralization in a thin Black Chernozem. Can. J. Soil
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Canadian Fertilizer Institute. 1998. Nutrient uptake and removeal by field crops. Western Canada.
Canadian Fertilizer Institute. Ottawa. 2pp.
Grant, C. A., Brown, K. R., Racz, G. J. and Bailey, L. D. 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.
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2005).
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(Accessed December 5, 2005).
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http://www.gov.mb.ca/agriculture/soilwater/manure/fdb01s01.html#summary. Accessed
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Winnipeg, Manitoba: University of Manitoba. 127 pp.
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