Phosphorus management for sensitive crops: Managing phosphorus through the rotation

Phosphorus management for sensitive crops: Managing phosphorus through the
rotation
Cynthia Grant, Agriculture and Agri-Food Canada, Brandon Research Centre, Box 1000A,
R.R.#3, Brandon, MB R7A 5Y3 E-mail: [email protected]
Abstract
Crop rotations in Manitoba are shifting towards greater production of crops such as soybean
and canola that are sensitive to seed-placed fertilizers. A high-yielding canola or soybean crop
will remove more phosphorus than can be safely applied in the seed-row, according to current
recommendations. Side-banding can increase the amount of P that can safely be applied at the
time of seeding. Both canola and soybean can effectively access phosphorus from the soil if
there are sufficient reserves present. In many fields in Manitoba, soil phosphorus levels are
relatively high due to long-term applications of manure or relatively high fertilizer phosphorus
inputs. In contrast, many other soils are deficient in phosphorus and those deficiencies will be
increased if more phosphorus is removed from the soil than is returned over time. The risk of
soil depletion becomes greater with more frequent production of soybean and canola in the
rotation if phosphorus applications are restricted to recommended seed-placed levels.
Therefore, it is important to consider phosphorus input and off-take throughout the cropping
sequence so that phosphorus can be managed in a way to optimize crop yield while avoiding
either excess accumulation or depletion over time. This may be done by modifying the method
of phosphorus fertilization in sensitive crops to allow applications that match crop removal.
Manure can be a valuable P source, where available. Alternately, greater phosphorus inputs
can be applied at other stages in the cropping sequence to compensate for the deficits in the
sensitive crops and balance phosphorus input and off-take over time.
Introduction
Phosphorus fertilizer is a major input for crop production in Manitoba. Phosphorus is critical in
the metabolism of plants, playing a role in cellular energy transfer, respiration, and
photosynthesis. Phosphorus is also a structural component of the nucleic acids of genes and
chromosomes and of many coenzymes, phosphoproteins and phospholipids. An adequate
supply of P is essential from the earliest stages of plant growth, since phosphorus is required for
all the growth processes required for seedling germination and establishment. Symptoms of P
deficiency include decreased plant height, dark green or purpling coloration, delayed leaf
emergence, reductions in tillering, secondary root development, and dry matter yield and seed
production.
Banding phosphorus near the seed improves phosphorus response
If P supplied from the soil and seed reserves is inadequate to support optimum crop yield,
fertilizer applications can supply P to the plant. Phosphorus supply during the first two to six
weeks of growth tends to have a large impact on final crop yield in most crops; therefore, it is
important that P fertilizer applications are managed in a way that ensures early season access
of the fertilizer by the growing crop.
Banding in or near the seed-row is the recommended placement method for phosphorus
fertilizer on the prairies. Studies reported in the Westco training manual indicated that banding
20 kg phosphate ha-1 near the seed-row was as effective as broadcasting and incorporating 80
kg phosphate ha-1. Banding the P near the seed-row puts the fertilizer in a position where the
roots can contact it early in growth, increasing the early season P supply. A large number of
studies in many plant species have shown that early season P supply is critical for optimum
crop yield. Withholding P during early plant growth will limit crop production and cause a
restriction in crop gro
owth from wh
hich the plan
nt may not re
ecover. Pho
osphorus limitation later in
the seaso
on has a mu
uch smaller impact
i
on crrop productio
on than do liimitations ea
arly in growth.
Concentrration of P in
n the soil sollution is usua
ally low sincce when pho
osphate is ad
dded to the ssoil,
it reacts relatively quickly with ca
alcium (Ca), magnesium
m (Mg), and iron (Fe) and
d aluminum (Al)
to form le
Most phosp
ess soluble phosphates.
p
phate movess to the plan
nt by diffusion rather than
n
mass flow
w, and as P movement through
t
the soil to the ro
oot is restrictted, diffusion
n is generallly
considere
ed to be the rate-limiting
g factor in P absorption b
by plants. It is estimated
d that, on
average, phosphate could only diffuse
d
appro
oximately 0.2
2 to 0.5 mm,, so that onlyy phosphate
e
within 0.5
5 mm of a pllant root is in
n a position where it can
n be accesse
ed by the cro
op. Placing the
fertilizer near the see
ed-row allow
ws the first plant roots to contact the fertilizer and
d begin upta
ake
early in growth.
g
As th
he crop root system grow
ws, it is able
e to access P from a larg
ger volume o
of soil
and begins to rely les
ss on the P from
f
the ferttilizer near th
he seed and
d more from P in the bulkk soil
(Figure 1). Having a combination
n of P bande
ed near the sseed-row an
nd an adequa
ate
concentrration of P in the bulk soil provides th
he plant with
h the P required through
hout the grow
wing
season.
eed-placed P fertilizer a nd from the bulk soil in tthree crops
Figure 1:: Absorption of P from se
through the
t growing season (Kallra and Sope
er 1968).
Uptake of
o P by the plant is propo
ortional to the root densi ty, so enlarg
gement of th
he root surface
area incrreases the ability of the plant
p
to acce
ess and abso
orb P from tthe soil. Therefore, manyy
plants respond to low
w soil P conc
centrations by
b enlarging the root sysstem and de
eveloping hig
ghly
branched
d roots with abundant
a
ro
oot hairs to enhance
e
theiir ability to explore new ssoil reservess of
gh P are encountered. Having the
P and effficiently extra
act P from th
he soil when
n areas of hig
e opportunitty for the pla
fertilizer placed in a band
b
near th
he seed-row provides the
ant to contacct the
fertilizer granule
g
and to begin roo
ot proliferatio
on in the hig
gh-concentra
ation reaction
n zone. Thiss
increases
s the plant’s
s ability to utiilize the fertilizer when itt is needed tto plant esta
ablishment. Cold
soil temp
peratures slo
ow diffusion of P in soil, reduce P so
olubility and d
decrease root growth.
Therefore
e, under typical Prairie conditions
c
att planting, co
old soil temp
peratures at seeding ma
ay
increase the benefit of
o banding P near the se
eed-row.
Stand Density (plants m-2)
Phosphorus deficit in sensitive crops
While seed-placed phosphorus is an efficient method of fertilizer placement, excess seedplaced P may lead to seedling damage in sensitive crops (Figure 2). Canola, soybean and flax
are all sensitive to seedling damage from monoammonium phosphate fertilizer, with stand
density decreasing mainly due to the salt effect from the N portion of the fertilizer. Blending
ammonium sulphate and monoammonium phosphate together can increase the damage
additively. Because of the sensitivity of canola, soybean and flax to seedling damage, the
amount of phosphate fertilizer that can be safely applied with the seed is low. If the provincial
guidelines for safe placement of phosphate fertilizer with the seed are followed for canola and
soybean, a good crop will remove more P from the soil than is added (Table 1). The simplest
way of avoiding this problem is to shift the placement of the phosphate away from the seed-row.
Applying the fertilizer as a side-band near the seed-row provides greater seedling safety yet is
still an efficient method of P placement. However, if the fertilizer is more than an inch or two
away from the seed-row, it may not be in a position where the roots can access it early in the
season and so may not provide the crop a starter benefit.
110
100
0 kg S ha-1
9 kg S ha-1
90
18 kg S ha-1
80
70
60
50
40
0
10
20
30
40
Phosphate (kg ha-1)
Figure 2: Impact of seed placed monoammonium phosphate and ammonium sulphate on stand
density of canola (Grant and Grenkow unpublished).
Table 1: Balance between phosphate removal and recommended safe limits for seed-placed
monoammonium phosphate for common Manitoba crops
Yield
Removal
Seed Limit
Balance
Crop
bu/acre
lb/acre
lb/acre
lb/acre
Wheat
40
29
50
21
Canola
40
40
20
-20
Soybeans
40
32
10
-22
Barley
80
38
50
12
Flax
32
20
20
0
Peas
50
38
20
-18
Oats
100
29
50
21
Historically in Manitoba, inputs of phosphate fertilizer and off-take of P in the plant was fairly
well-balanced, because shortfalls in P input during production of canola was compensated by
higher additions in the cereal years. However, cropping patterns in Manitoba are changing, with
higher production of canola and soybean and lower production of cereal crops (Table 2). If
removal of P is greater than input of P over time, the soil may become P depleted. Conversely
if input of P exceeds P removal over time, as may occur with manure applications, soil P levels
may increase. Long-term studies conducted by Fernando Selles at the AAFC research centre in
Swift Current showed a good relationship between Olsen-P soil phosphorus levels and the
balance between P applied and P removed in the crop (Figure 3).
Table 2: Production of various field crops (000 acres) in Manitoba between 2001 and 2012
(Statistics Canada).
Crop
Wheat
Canola
Soybeans
Barley
Peas
Flaxseed
Oats
Corn (grain)
2001
3922
1872
50
1165
148
436
905
110
2006
3280
2279
350
838
91
384
946
150
70
P build-up
P depletion
-1
Olsen-P (kg ha )
60
2012
2940
3485
875
490
55
180
565
300
k and 95% confidence Interval
50
40
intercept and 95% confidence interval
30
20
10
-120
-100
-80
-60
-40
-20
0
20
40
-1
P-balance (kg ha )
y  25  0.08 * Pbal
when Pbal <= k
y  25  0.08 * Pbal  1.1* ( Pbal  k ) otherwise
Figure 3: Soil test P values reflected the balance between P input and P removal in the crop in
long-term studies conducted at Swift Current, Saskatchewan (Selles et al. 2011).
Similar results were found in studies across the prairies that evaluated the effect of annual
inputs of approximately 0, 40, 80 and 160 lb of phosphate per acre from 2002 to 2010, in a
durum wheat-flax cropping sequence (Figure 4). In these studies, withholding P fertilizer led to
a large depletion in soil P while applications of 80 lb ac-1 or above led to a large increase.
Application of 40 lb ac-1 produced minor changes in soil-test P, depending on the soil type. In
this study, similar rates of P were applied to both crops in the rotation, even though the flax crop
tends to remove lower amounts of P. In rotations with canola that removes greater amounts of
P than are normally applied, the depletion would be greater than observed with this study.
80
70
Carman
60
Carstairs
Change in Olsen P (ppm)
Brandon
50
Ft. Sask
40
Phillips
30
20
10
0
‐10
0
40
80
120
160
‐20
Phosphate applied annually (lb/ac)
Figure 4: Change in Olsen P values with annual P application after 8 years of cropping
following a durum wheat-flax cropping sequence on five soils in Western Canada (Grant et al.,
unpublished).
Either excess depletion or excess accumulation of P in soils can cause problems. Excess P
accumulation can increase the risk of P movement into water bodies, leading to eutrophication,
as is currently seen in in Lake Winnipeg. Conversely, depletion of soil P can reduce the supply
of P from the soil to the crop, potentially limiting yield, especially in situations where the P
application is reduced to meet safe limits for seed-placement. Where soils are depleted, the
plant may not be able to access sufficient P from the soil to optimize yield. Studies conducted in
Saskatchewan evaluated the effect of applications of seed-placed MAP on soils with and
without application of initial large rates of broadcast MAP (Figure 5). Seed-placed P alone was
not sufficient to optimize crop yields on soils that had very low background P levels, as
measured by Olsen P. In order to maintain the long-term productivity of the soil, it is important to
manage phosphorus through the rotation to maintain reasonable levels of available soil P, in the
range of 15 ppm.
Figure 5:: Effect of a single broad
dcast and an
nnual seed-p
placed phossphate appliccations on w
wheat
grain yield (Wager ett al. 1986).
While it is
s often state
ed that the effficiency of phosphate
p
fe
ertilization in
n the year off application is
low, in th
he range of 30%
3
or less, the P that is
s not used b
by the crop in
n the year off application will
normally remain available to follo
owing crops,, unless it is removed fro
om the field by run-off orr
erosion. When phos
sphorus fertillizer is applie
ed to a soil, it initially disssolves and enters the ssoil
solution, but this shiffts the equilib
brium toward
ds precipitattion of P as C
Ca, Mg, Fe o
or Al-phosph
hates
that have
e a lower sollubility than the
t fertilizer that was ap
pplied. A larg
ge proportion
n of these
phosphate compounds still rema
ain predomin
nantly in "lab
bile" forms th
hat can be acccessed by the
plant ove
er time. As th
he plant feed
ds on the P in the soil so
olution, it shiifts the equillibrium back
towards the
t dissolution of these phosphates in order to rreplenish the
e soil solutio
on (Figure 6)).
So, in an
ny particular season, the plant will ac
ccess newly applied P frrom the fertilizer, P that had
recently precipitated and re-disso
olved from the fertilizer a
applied in th
hat season, a
as well as P
derived from
f
fertilizer that had be
een applied and precipittated in prevvious years. The <30%
figure forr nutrient use
e efficiency that
t
is often used refers to the amou
unt of P reco
overed in a
single cro
op from the fertilizer thatt was applie
ed in that gro
owing season. When yo
ou consider tthe
recovery of fertilizer P over multiple years, th
he fertilizer u
use efficienccy is substan
ntially higherr.
Studies in Rothamsta
ad, England showed P recoveries
r
o
over time of g
greater than 90% while in
Swift Currrent, SK, ne
early all of th
he P fertilizer applied wa
as recovered
d over time iff N was not
deficient (Figure 7).
Figure 6:: Phosphorus that is precipitated as sparing solu
uble phosphates can rem
mobilize to
replenish
h the soil solution when iti is depleted
d by plant up
ptake. Preciipitation-disssolution is a two
way reac
ction.
b Selles et al.
a (2011), lo
ong-term mu
ulti-year reco
overy of applied
Figure 7:: In studies conducted by
phosphate fertilizer approached
a
100% when nitrogen wa
as not limitin
ng.
The long-term availa
ability of phos
sphorus in th
he labile poo
ol provides a number of options for
enhancin
o apply veryy
ng the P sup
pply through the rotation for sensitive
e crops. One option is to
large sing
gle applications of P ferttilizer, partic
cularly if P fe
ertilizer prices were low ffor some rea
ason.
In studies
s conducted
d by Bailey et
e al. (1977) in two locati ons in Manittoba, a singlle broadcastt
applicatio
on of 200, 40
00 or 800 lb P2O5 ac-1 in
ncreased cro
op yields and
d maintained
d soil P at le
evels
above the deficiency
y level, even after eight years
y
of crop
pping. Simila
ar results we
ere seen in the
W
(1986
6) shown in Figure 5.
work by Wager
The high cost may make
m
applica
ation of such large amou
unts of P ferttilizer unattra
active. A mo
ore
economic
c approach may be to ta
ake advantag
ge of the live
estock manu
ure that is avvailable in th
he
province. Livestock manure is rich is phosph
hate, with ra
atios of availa
able N:P2O5 usually belo
ow
1:1. How
wever, plants
s require and
d remove a N:P2O5 ratio
o in the range of 2 to 3:1. Therefore
e,
applying manure at a rate to satisfy the N de
emands of a crop will ap
pply much mo
ore P that th
he
crop requ
uires and ca
an provide su
ufficient P fo
or several ye ars of crop p
production (T
Table 3).
Table 3: Liquid hog manure
m
or so
olid cattle manure applie
ed at a rate tto supply cro
op N
requirem
ments will sup
pply several years of P needs
n
(Courrtesy of Don Flaten).
1
Manure analyses are from the Tri-Provincial Ma
anure Applica
ation and Use
e Guidelines
Assumes all manure is spring applied, by subsu
urface injectio
on, with no sig
gnificant volattilization loss of
NH4-N
2
3
Assumes that P is rem
moved as gra
ain only.
Phospho
orus may also be built up
p in the soil more
m
gradua
ally, by using
g maximum recommend
ded
seed-row
w application
n rates of P in crops such
h as wheat o
or barley tha
at are toleran
nt of seed-pllaced
MAP. In studies con
nducted at tw
wo locations in Manitoba
a, P concentration in the tissue of fla
ax at
six weeks was increa
ased by application of P fertilizer to preceding w
wheat or canola crops,
indicating
g that P from
m the preced
ding year rem
mained availlable for the flax to use ((Figure 8).
Although
h the flax see
ed yield in th
his study did not increase
e with the P applied eith
her to the
preceding crop or dirrectly as a siide-band application to tthe flax itselff, the increase in tissue P
indicates
s that P applied to preceding crops will
w remain a vailable and
d so P can be managed
through the
t rotation to
t improve P status of se
ensitive crop
ps (Figure 8).
nola or whea
at at two Man
nitoba locations (RCFigure 8:: Effect of P applied as MAP to Can
Research
h Centre and
d NTF – No--till Farm) on
n P concentrration in the following fla
ax tissue at ssix
weeks off growth (Gra
ant et al. 200
09).
Summarry
Crop rota
ations in Manitoba are in
ncluding larg
ge proportion
ns of crops ssuch as soyb
bean and ca
anola
that are sensitive
s
to seed-placed
s
d fertilizers. A high-yield
ding canola o
or soybean ccrop will rem
move
more pho
osphorus tha
an can be sa
afely applied
d in the seed
d-row, accorrding to curre
ent
recomme
endations. If the P remo
oved in the harvested
h
cro
rop is not rep
placed throu
ughout the
rotation, soils may be
ecome deple
eted over tim
me. The risk of soil deple
etion becomes greater w
with
more freq
quent production of soyb
bean and ca
anola in the rrotation if ph
hosphorus applications a
are
restricted
d to recommended seed
d-placed leve
els. Therefo
ore, it is impo
ortant to con
nsider
phosphorus input and off-take th
hroughout the
e cropping ssequence so
o that phosphorus can be
managed
d in a way to
o optimize crrop yield whiile avoiding either excesss accumula
ation or deple
etion
over time
e. This may be done by modifying th
he method off phosphoru
us fertilization
n, for examp
ple
using sid
de-banded or mid-row ba
anded P, in sensitive
s
cro
ops to allow applicationss that match crop
removal. Where avaiilable, manu
ure applicatio
on can be a good source
e of P for several crops.
Alternate
ely, greater phosphorus
p
inputs can be
b applied att other stage
es in the cropping seque
ence
to balanc
ce phosphorrus input and
d off-take over time. Ma
aintaining go
ood soil fertiliity while usin
ng
starter P near the seed-row to prrovide adequ
uate early se
eason P, particularly on cold soils, ccan
provide sensitive
s
cro
ops with the P required to
o optimize yyield.
Reference
Bailey, L. D., Spratt, E. D., Read, D. W. L., Warder, F. G. and Ferguson, W. S. 1977. Residual
effects of phosphorus fertilizer. II. For wheat and flax grown on Chernozemic soils in Manitoba.
Can. J. Soil Sci. 57, 263-270.
Grant, C. A., Monreal, M. A., Irvine, R. B., Mohr, R. M., McLaren, D. L. and Khakbazan, M.
2009. Crop response to current and previous season applications of phosphorus as affected by
crop sequence and tillage. Can. J. Plant Sci. 89, 49-66.
Kalra, Y. P. and Soper, R. J. 1968. Efficiency of rape, oat soybean and flax in absorbing soil and
fertilizer phosphorus at seven stages of growth. Agron. J. 60, 209-212.
Selles, F., Campbell, C.A., Zentner, R.P., Curtin, D., James, D.C., Basnyat, P. 2011.
Phosphorus use efficiency and long-term trends in soil available phosphorus in wheat
production systems with and without nitrogen fertilizer . Can. J. Soil; Sci. 91:39-52.
Wager, B.I., J.W.B. Stewart, and J.L. Henry. 1986. Comparison of single large broadcast and
small annual seed-placed phosphorus treatments on yield and phosphorus and zinc contents of
wheat on Chernozemic soils. Can J. Soil Sci. 66:237-248.