RESEARCH ARTICLE
Calcula ion o h eshold Olsen P alues o e ilize esponse
om soil p ope ies
Rami o Recena
1
&Isabel Díaz
2
&Ma ía Ca men del Campillo
3
&José To en
3
&
An onio Delgado
1
Accep ed: 28 July 2016 /Published online: 23 Sep embe 2016
#INRA and Sp inge -Ve lag F ance 2016
Abs ac Phospho us (P), a non- enewable esou ce,
needs o be used mo e e icien ly in ag icul u e. This e-
qui es using soil P es s. Howe e , he P es h eshold
alues o e ilize esponse depend on many soil p op-
e ies, some o which may be use ul o es ima e hese
h eshold alues, o he s no . The e o e, we sea ched he e
which soil p ope ies a e use ul o es ima e P h eshold
alues. We calcula ed he h eshold alues o Olsen P
and 0.01 M CaCl
2
ex ac able P o 18 ep esen a i e ag-
icul u al soils o he Medi e anean egion o Spain. Fo
ha , we pe o med a P s a a ion expe imen in which
whea and sun lowe we e al e na i ely po -c opped.
Resul s show ha Olsen P h eshold alues a e nega i ely
co ela ed o P bu e capaci y ( o −0.74, P lowe han
0.001), clay con en (−0.82, 0.001), pH (−0.76, 0.001),
and Fe oxide con en (−0.55, 0.05). Mul iple eg ession
models in ol ing clay, pH o soil o ganic C, and phos-
pha ase ac i i y o o ganic hyd olysable P accoun ed o
as much as 87 % o he a iance in calcula ed Olsen P
h eshold alues. In pa icula , he e is a majo e ec o
o ganic P on Olsen P h eshold alues. Single models
based on ou inely measu ed soil p ope ies such as clay
con en and pH made accu a e p edic ions o Olsen P
h eshold alues wi h
2
o 0.81 and P lowe han 0.001.
Keywo ds Olsen P .A ailabili y index .Th eshold alues .
Bu e capaci y .O ganic P
1 In oduc ion
Ag icul u e depends on he use o phospho us (P) e ilize s
ob ained om phospha e ock, which is a non- enewable and
s a egic esou ce (Keyze 2010; Van Vuu en e al. 2010). The
demand o P e ilize s is expec ed o g ow as he logical esul
o he g owing ood needs o an inc easing popula ion, whe e-
as he p oduc ion o PR is expec ed o peak in he nex decades
(Sch öde e al. 2011;Ryane al.2012). Expec ed u u e P
sca ci y is hus eme ging as a global challenge o humankind
(Co dell and Nese 2014). In addi ion, he use o P in ag icul-
u e is globally e y ine icien , in such a way ha only 15 %
o P applied o ag icul u al soil goes in o he ood chain
(Co dell e al. 2009; Wi he s e al. 2014).
The o me conside a ions poin o he need o a mo e
e icien and sus ainable use o P in ag icul u e. In pa icu-
la , e iliza ion schemes should ely, among o he ac o s,
on accu a e dis inc ion o P- esponsi e si es (Recena e al.
2015) in o de o concen a e his esou ce on soils in which
he highes e u n o P e iliza ion is o be expec ed. This
dis inc ion is usually assessed wi h he use o an “a ailable
P es ”o a “soil P es ” ha is co ela ed wi h plan P
up ake. The e is no a uni e sal soil P es alid o e y
di e en soils, and only o Eu ope, 16 soil P es s ha e
been p oposed (Ney oud and Lische 2003; Delgado and
Scalenghe 2008). Commonly used soil P es s a e based
on ex ac ion wi h a chemical eagen , as is he case o
wo ldwide used Olsen P es (Olsen e al. 1954). The key
issue o hei p ac ical use is he de ini ion o h eshold
alues below which yield esponse o e ilize applica ion
can be expec ed (Delgado and Scalenghe 2008;Tange al.
*An onio Delgado
[email protected]
1
Depa amen o de Ciencias Ag o o es ales, ETSIA, Uni e sidad de
Se illa, C a. U e a km 1, 41013 Se illa, Spain
2
Depa amen o de Mecánica de Fluidos e Ingenie ía Ae oespacial,
ETSIA, Uni e sidad de Se illa, C a. U e a km 1,
41013 Se illa, Spain
3
Depa amen o de Ag onomía, Uni e sidad de Có doba, Edi icio C4,
Campus de Rabanales, 14071 Có doba, Spain
Ag on. Sus ain. De . (2016) 36: 54
DOI 10.1007/s13593-016-0387-5
2009). Howe e , al hough soil P es s a e deemed o be
use ul o assessing P e ilize needs, hey can be inaccu-
a e because he de ini ion o hei h eshold alues is no
always p ecise. In ac , ac ual h eshold alues o a gi en
es can ange widely among hose soils o which i s use is
ecommended, e.g., o Olsen P (Delgado e al. 2010;
Sánchez-Alcalá e al. 2015). Thus, Olsen P is no always
well ela ed o plan P up ake (Delgado and To en 1997;
Kulhánek e al. 2007; Tandy e al. 2011). In soils wi h e y
simila p ope ies, Delgado e al. (2010) obse ed a wide
ange in h eshold alues o Olsen P, which clea ly
depended on he soil P bu e capaci y. Sánchez-Alcalá
e al. (2014) epo ed ha he h eshold alues o Olsen P
we e a ec ed by p ope ies ela ed o he P so p ion capac-
i y o he soil such as ca bona e and Fe oxides con en s.
These h eshold alues we e es ima ed conside ing ha
plan s can abso b su icien P abo e a gi en P concen a ion
in solu ion. Howe e , ecen s udies ha e e ealed ha P
concen a ion in soil solu ion o a su icien P supply may
di e om one soil o ano he (Sánchez-Alcalá e al. 2015).
The e is no much in o ma ion on soil p ope ies con olling
his h eshold P concen a ion in solu ion. In o he plan
g ow h expe imen s, ca bona e con en and pH we e he
soil p ope ies a ec ing Olsen P h eshold alues
(Sánchez-Alcalá e al. 2015). Recena e al. (2015)demon-
s a ed ha he Olsen P p edic i e alue o plan P up ake is
a ec ed no only by hose soil p ope ies in luencing he
equilib ium be ween ino ganic phospha e in solu ion and
ha in solid phase bu also by ac o s ela ed o o ganic P
dynamics. Howe e , hey did no p o ide e idence o how
h eshold alues o Olsen P we e a ec ed by all hese soil
p ope ies. In spi e o all hese con ibu ions, he e is no a
whole iew o all po en ial soil ac o s a ec ing h eshold
alues o a gi en soil P es . I can be hypo hesized ha
he e is a need o mo e p ecise me hods o es ima e P-
esponsi e si es. One possibili y is he de elopmen o es s
based on mo e complex P ex ac ion me hods such as hose
using esins (Delgado e al. 2010) o di usi e g adien s hin
ilms (Tandy e al. 2011; San ne e al. 2015), which a e
mo e sensi i e o soil P bu e capaci y. Ano he op ion is
he de elopmen o single models ha a e based on adi-
ional soil P es s such as Olsen P in combina ion wi h soil
p ope ies ela ed o he dynamics o soil P. This would
mean ha h eshold alues could be accu a ely es ima ed
on he basis o ou inely de e mined soil p ope ies. These
models should ely on a deepe knowledge on hose soil
p ope ies a ec ing he ela ionship be ween plan P up ake
and chemically ex ac able soil P. In his ega d, he objec-
i es o he p esen s udy we e as ollows: (i) iden i ica ion
o soil p ope ies a ec ing h eshold Olsen P alues o
e ilize esponse in a se o ep esen a i e Medi e anean
soils whe e his es is usually ecommended and (ii) o
de elop simple models based on ou inely de e mined soil
p ope ies o es ima e accu a e h eshold alues o use o
Olsen P as soil P es in hese soils.
2 Ma e ials and me hods
2.1 Soils
The se o soils used in his s udy was he same one as used by
Recena e al. (2015), wi h one addi ional soil included (18
soils in o al). The soils we e classed as Mollisols, En isols,
Incep isols, Al isols, and Ve isols acco ding o soil axonomy
(Soil Su ey S a 2010). The ag icul u al use o hese soils
wasde ailedinRecenae al.(2015), and he addi ional soil
conside ed was used o he ypical biannual ain- ed c op
o a ion in Spain, i.e., whea –sun lowe . The main p ope ies
o he 0–20-cm soil laye , om which samples we e aken, a e
desc ibed in Table 1.
Me hods o soil sampling, p ocessing, analysis o basic
p ope ies, s udy o P and Fe o ms, and P so p ion capaci y
om P so p ion iso he ms a e desc ibed in Recena e al.
(2015). I on o ms included ci a e-asco ba e ex ac able Fe
(Fe
ca
), mainly ela ed o poo ly c ys alline Fe oxides, and
ci a e-bica bona e-di hioni e ex ac able Fe (Fe
d
), mainly e-
la ed o c ys alline Fe oxides. In addi ion, he concen a ion o
phy ase hyd olysable P in he alkali (NaOH) and ci a e-
bica bona e ex ac s o he sequen ial ac iona ion scheme
desc ibed by Recena e al. (2015) o s udy P o ms was also
de e mined. These ex ac s in he sequen ial ac iona ion
scheme a e supposed o con ain ino ganic and o ganic P mos -
ly adso bed o p ecipi a ed as soluble me al phospha es
(Saa ed a e al. 2007). The phy ase hyd olysable P was es i-
ma ed as he inc ease in molybda e eac i e P (Mu phy and
Riley 1962) a e 30 min o incuba ion o he ex ac wi h
phy ase (Bio-Feed phy ase L, No ozimes, Bags ae d,
Denma k) a 37 °C. To his end, he enzyme was added o
he soil ex ac in 0.2 ml o bu e solu ion p epa ed wi h
0.4 M C
2
H
4
O
2
and 10 mM e hylenediamine e aace ic acid
a pH 5.5 o a inal ac i i y o 10 nKa ml
−1
and he eac ion
was s opped by adding 15 % ichlo oace ic acid.
Phospho us concen a ion in 0.01 M CaCl
2
ex ac s
(P
CaCl2
) was used as a p oxy o he concen a ion o P in
he soil solu ion. This ex ac ion was pe o med in dupli-
ca eanda asoil:ex ac an a ioo 1:10using2go soilin
20 ml o ex ac an in polye hylene alcon ubes ha we e
end-o e -end shaken a 2.5 s
−1
o 30 min. The ex ac was
cen i uged a 1000g o 10 min, and hen a po ion o 2 ml
cen i uged in Eppendo ubes a 19,000g o emo e soil
pa icles wi h a diame e >0.05 μm (Sánchez-Alcalá e al.
2015). In he emaining solu ion, molybda e eac i e P was
de e mined acco ding o Mu phy and Riley (1962). Olsen
P was de e mined as he molybda e eac i e P in bica bon-
a e ex ac s (Olsen e al. 1954).
54 Page 2 o 8 Ag on. Sus ain. De . (2016) 36: 54
As desc ibed by Recena e al. (2015), om a collec ion o
soil si es in which he indi idual samples anged widely in
Olsen P, hose soil samples wi h he wo ex eme Olsen P
alues we e selec ed om each si e and named “low-P”and
“high-P”samples acco ding o hei P s a us. The high-P and
low-P samples we e examined in o de o check ha hey
di e ed by less han 5 % in he main soil p ope ies. Fo he
expe imen desc ibed below, soil was g ound o <6 mm. Olsen
P le els in high-P samples we e all well abo e h eshold
alues o e ilize esponse acco ding o he cu en s age
o knowledge, e en in samples wi h he lowes alues
(9 mg kg
−1
) which we e samples wi h a e y high P bu e
capaci y and hus wi h expec ed h eshold alues below
5mgkg
−1
(Delgado e al. 2010). Fo mos low-P samples,
Olsen P was assumed o be close o h eshold alues (da a
no shown; means and ange in Recena e al. 2015).
2.2 Expe imen al se up
An expe imen in ended o deple e soil P was conduc ed in a
g ow h chambe (Fig. 1) whe e du um whea and sun lowe
we e g own un il an hesis wice, whe eby simula ing a ypical
ain- ed c op o a ion, o bo h high-P and low-P samples.
Thus, o each ype o sample o each soil, ou successi e
c ops we e g own. Polys y ene po s (5.5-cm diame e , 15-cm
high) illed wi h 300 g o soil we e used. Seeds we e p e-
ge mina ed on a mois ened Pe i pla e o 14 days and, a e
ha , ge mina ed in ays wi h pe li e as subs a e and i iga ed
wi h deionized wa e . A e 16 days, seedlings we e
ansplan ed. Fo each soil and sample, he numbe o po s
pe deple ion s age dec eased om i e in he i s s age o
wo in he las one because 300 g we e emo ed a e each
s age o u he labo a o y analysis. A e ansplan ing, po s
we e wa e ed daily wi h 20 ml o a Hoagland- ype nu ien solu-
ion wi hou phospho us a pH 6–6.5, sandwiching be ween h ee
i iga ions and one wi h he same olume o deionized wa e o
a oid saliniza ion o he soil. Plan s we e g own wi h a 14-h
pho ope iod, a ela i e humidi y o 45 % (day pe iod) and
60 % (nigh pe iod), and an ac i e pho osyn he ic adia-
ion o 22 W m
−2
. The composi ion o he solu ion applied
was he ollowing (all concen a ions in mM l
−1
): MgSO
4
(2), Ca(NO
3
)
2
(5), KNO
3
(5), KCl (0.05), Fe-EDDHA
(0.01), H
3
BO
3
(0.009), MnCl
2
(0.0023), CuSO
4
(0.0005), ZnSO
4
(0.002), and H
2
MoO
4
(0.0005).
2.3 Plan and soil analysis a e c opping
A e each c opping, plan shoo s and oo s we e ca e ully
sepa a ed, washed, and inally d ied in a o ced ai o en
un il cons an weigh a 65 °C o a leas 48 h. Roo and
shoo d y ma e was hen measu ed. A e each c opping
s ep, soil om all he eplica ions o each soil and ype o
sample was mixed and p ocessed by d ying and g ounding
Table 1 Mean, s anda d de ia ion (SD), and ange o he p ope ies o s udied soils (n= 18), including ini ial Olsen P in high-P samples, ci a e-asco ba e ex ac able Fe (Fe
ca
), ci a e-bica bona e-
di hioni e ex ac able Fe (Fe
d
), phy ase hyd olysable P in he NaOH (NaOH
h
), and ci a e-bica bona e (CB
h
) ex ac s o high-P samples; mean o he phospha ase ac i i y in he ou c ops in high-P samples;
cons an s A and b in he F eundlich equa ion (Y + Yo = A •X
1/b
) in high-P samples; and P bu e capaci y a h ee concen a ions in solu ion equilib ium (e), 0.2 mg P l
−1
,and1mgPl
−1
Gene al soil p ope ies
Clay Soil o ganic C Ca ca bona e equi alen Ac i e Ca ca bona e equi alen Fe
ca
Fe
d
pH Olsen P
gkg
−1
mg kg
−1
Mean ± SD 288 ± 155 10.6 ± 3.8 270 ± 234 81 ± 67 1.02 ± 0.74 5.52 ± 3.05 7.8 ± 0.5 24 ± 10
Range 48–640 5.5–20 0–723 0–178 0.17–2.44 2.04–13.24 6.5–8.3 9.1–49.1
O ganic P- ela ed p ope ies
NaOH
h
CB
h
Phospha ase
mg kg
−1
mg PNP kg
−1
h
−1
Mean ± SD 5.21 ± 5.25 7.0 ± 4.6 142 ± 18
Range 0.48–24.02 0–13.5 105–172
P ope ies ela ed o P adso p ion
AbBu e capaci y
e
Bu e capaci y
0.2
Bu e capaci y
1
Mean ± SD 72 ± 32 2.22 ± 0.31 348 ± 413 78 ± 35 32 ± 14
Range 16–140 1.52–2.64 9–1480 18–151 8.5–67
Th eshold alues o Olsen P and P concen a ion in CaCl2 ex ac s (P
CaCl2
)andP alues and R
2
o he Ca e-Nelson model
P
CaCl2
P alues R
2
Olsen P P alues R
2
mg l
−1
mg kg
−1
Mean ± SD 0.025 ± 0.043 0.0203 ± 0.0240 0.72 ± 0.14 9.2 ± 3.2 0.0326 ± 0.038 0.68 ± 0.19
Range 0.002–0.175 0–0.0868 0.47–0.96 4.9–16.5 0–0.1065 0.38–0.96
Median 0.006 0.0117 0.74 8.9 0.0164 0.69
Subsc ip s o bu e capaci y: e, es ima ed a equilib ium concen a ion; 0.2, es ima ed a 0.2 mg l-1 P in he solu ion; and 1, es ima ed a 1 mg l-1 P in he solu ion
Ag on. Sus ain. De . (2016) 36: 54 Page 3 o 8 54
o 6 mm; 300 g o soil was wi hd awn o chemical anal-
ysis and g ound o pass a 2-mm sie e. In hese samples,
molybda e eac i e P in bica bona e and 0.01 M CaCl
2
ex ac s was de e mined as desc ibed p e iously.
2.4 Da a analysis
Da a om high- and low-P samples we e analyzed as a unique
se o da a o each soil. D y ma e yield o whea and sun-
lowe was exp essed on a ela i e basis conside ing as he
maximum yield he a e age d y ma e ob ained in high-P
samples o whea and sun lowe in hei i s c op. Because
Olsen P alues we e gene ally abo e 12 mg kg
−1
be o e he
i s sun lowe c op (da a no shown), and sun lowe is e y
e icien in ex ac ing P (Delgado and To en 1997), sun low-
e d y ma e yield was no es ic ed; only wo soils showed
lowe Olsen P alues be o e sun lowe (6 and 9) which we e
conside ed non-limi ing due o he high P bu e capaci y o
he soil (Delgado e al. 2010). Th eshold alues o Olsen P
and P
CaCl2
we e es ima ed acco ding o he Ca e and Nelson
me hod (1971). This me hod p o ides h eshold alues o
each P ex ac ion below which he yield signi ican ly de-
c eased om he maximum ela i e yield de ined o each soil
and seems mo e accu a e o de ine h eshold alues o soil P
es han o he me hods such as he linea o quad a ic pla eau
i ings o he Mi sche lich- ype equa ions (Malla ino and
Blackme 1992). The c i ical le el o he Ca e-Nelson model
was es ima ed as ha alue o he soil P es (P
CaCl2
o Olsen
P) ha maximized he sum o squa es be ween wo popula-
ions o soil P es alues, i.e., abo e and below h eshold
alues (Geng e al. 2014), using he ANOVA op ion o
S a g aphics 5.1.
3 Resul s and discussion
The se o soils used in his s udy anged widely in p ope ies
ela ed o P dynamics (Table 1). Rega ding phy ase hyd olys-
able P, his can be assumed o be mainly monoes e s which
can be po en ially hyd olyzed by he ac ion o hizosphe e
enzymes and can po en ially con ibu e o P up ake by plan s.
On a e age, amoun s o hese monoes e s adso bed o p ecip-
i a ed as soluble me al phospha es we e no negligible since
hey we e equi alen o hal o he bica bona e ex ac able
ino ganic P in soil (Olsen P, Table 1). As expec ed, he soil
P bu e capaci y was posi i ely co ela ed o clay con en
(Shi ani e al. 2005) and he con en o Fe ela ed o Fe oxides
in soil (Fe
ca
+Fe
d
). On he con a y, soil P bu e capaci y was
nega i ely co ela ed wi h he a io o Fe in poo ly c ys alline
oxides o ha in c ys alline oxides (Fe
ca
/Fe
d
)(Table2shows P
bu e capaci y a 1 mg l
−1
). This nega i e co ela ion is ex-
plained by he usual lowe a ini y o P o poo ly ela i e o
highly c ys alline Fe oxides (Colombo e al. 1994). I on in Fe
oxides and he Fe
ca
/Fe
d
a io we e co ela ed wi h clay con en
(Table 2) hus e ealing ha oxides a e pa o he clay ac ion
bu also ha he a io o poo ly c ys alline o c ys alline Fe
oxides inc eased wi h dec eased clay con en in soil. On he
o he hand, he Fe in Fe oxides was nega i ely co ela ed wi h
he ac i e calcium ca bona e equi alen , e idencing ha min-
e al wea he ing and subsequen p ecipi a ion o oxides du ing
soil genesis is inhibi ed when soil pH is bu e ed by ca bona e.
O e all, he Ca e-Nelson model p o ided easonable es i-
ma es o h eshold alues o bo h soil P es s: median alues
o he po ion o a iance explained was 69 % o Olsen P and
74 % o P
CaCl2
(Table 1). Th eshold alues o Olsen P we e
in he ange usually obse ed in ield expe imen s (Colomb
e al. 2007; Bai e al. 2013) and we e simila o hose desc ibed
by Delgado e al. (2010) in po expe imen s using a simila
amoun o soil. Obse ed h eshold alues o his soil P es
anged widely be ween soils (Table 1). Such a deg ee o a -
iabili y in h eshold alues o Olsen P was obse ed by
Delgado e al. (2010) in a g oup o clay soils wi h a na ow
ange o a ia ion in soil p ope ies. Sánchez-Alcalá e al.
(2015) also obse ed a wide ange o Olsen P and P
CaCl2
h eshold alues in a g oup o soils which, in ha case, anged
widely in hei p ope ies.
Th eshold alues o bo h indices we e posi i ely co ela -
ed, and o bo h es s, h eshold alues we e nega i ely co e-
la ed wi h clay (Table 2). In addi ion o clay, soil p ope ies
wi h which Olsen P h eshold alues we e co ela ed we e he
ollowing: pH, P bu e capaci y, and Fe in Fe oxides; hese
co ela ions being also nega i e (Table 2). Nega i e co ela-
ion wi h clay and Fe in Fe oxides e eals ha h eshold alues
dec eased wi h inc eased P so p ion capaci y o he soil. Since
clay and Fe oxide con en we e posi i ely co ela ed in he
g oup o soils s udied (Table 2), he ela i e con ibu ion o
clay and Fe oxides o he P dynamics is di icul o assess. Fo
he same P concen a ion in solu ion, P bu e capaci y usually
inc eases wi h inc easing P so p ion capaci y. This con ibu es
o explain he co ela ion o clay and Fe in oxides wi h soil P
bu e capaci y (Table 2), which may explain a leas in pa
he obse ed nega i e co ela ion o h eshold alues wi h clay
and Fe oxides.
As epo ed by Delgado e al. (2010), P bu e capaci y
seems o accoun o mo e a ia ion o he Olsen P h eshold
alues when i is measu ed a ela i ely high P concen a ion
in solu ion (1 mg l
−1
) a he han a low concen a ion (da a
no shown). Al hough he co ela ion o pH wi h P bu e
capaci y and clay makes i di icul o ex ac clea -cu con-
clusions, he e ec o pH can be also asc ibed no only o i s
in luence on soil P dynamics bu also by i s co ela ion wi h
o he mine alogical p ope ies, such as so ben su ace ype,
also a ec ing a ailabili y o plan s (Delgado and To en
1997). Th eshold alues o Olsen P can be accu a ely p e-
dic ed in ou soils om mul iple eg essions in ol ing di e -
en soil p ope ies. Clay con en , pH, and phospha ase ac i i y
54 Page 4 o 8 Ag on. Sus ain. De . (2016) 36: 54
in he hizosphe e explained nea 90 % o a ia ion in Olsen P
h eshold alues (Fig. 2a). In addi ion, clay, soil o ganic ca bon,
and he phy ase hyd olysable P in he ci a e-bica bona e ac ion
explained 75 % o a ia ion in h eshold alues o Olsen P
(Fig. 2b). These ela ionships e eal ha h eshold alues o
his soil P es was in luenced no only by hose ac o s a ec ing
he equilib ium o ino ganic phospha e be ween he solid and
liquid phases o soil, such as P bu e capaci y, bu also by
ac o s ela ed o o ganic P dynamics, such as he amoun o
hyd olysable o ganic P o he phospha ase ac i i y in he hizo-
sphe e. O e all, lowe h eshold alues can be expec ed wi h
inc eased con en s o hyd olysable o ganic P (Fig. 2b) due o
he con ibu ion o he o ganic P o plan supply. This con ibu-
ion is no aken in o accoun in usual soil P es which a e
based on he de e mina ion o ino ganic P (usually molybda e
eac i e) in soil ex ac s.
The wide ange o P
CaCl2
h eshold alues obse ed suppo s
he con en ion ha he P concen a ion in soil solu ion abo e
which he e is a su icien P up ake by plan s a ies widely de-
pending on soil p ope ies, consis en wi h p e ious esul s
(Sánchez-Alcalá e al. 2015). These alues we e a ec ed nega-
i ely by ac i e calcium ca bona e, and posi i ely by Fe
ca
/Fe
d
,
and hyd olysable o ganic P in NaOH and ci a e-bica bona e
ex ac s (Table 2;Fig.3). This e eals he po en ial con ibu ion
o o ganic P o P supply o plan s. The e ec o he a io Fe
ca
/Fe
d
on h eshold P
CaCl2
can be explained by he lowe a ini y o P o
poo ly ela i e o highly c ys alline Fe oxides. This implies ha a
highe P concen a ion in solu ion can be in equilib ium wi h he
Table 2 Co ela ion coe icien s be ween di e en p ope ies o s udied
soils: h eshold alues (TV) o Olsen P and P in 0.01 M CaCl
2
ex ac s
(P
CaCl2
), clay, pH, mean o he phospha ase ac i i y in he ou c ops in
high-P samples, o ganic C, ac i e Ca ca bona e equi alen (ACCE), Fe in
Fe oxides (Feca + Fed), a io o ci a e-asco ba e o ci a e-bica bona e-
di hioni e ex ac able Fe (Fe
ca
/Fe
d
), P bu e capaci y a 1 mg P l
−1
(PBC
1
), phy ase hyd olysable P in ci a e-bica bona e ex ac s (CB
h
),
and he sum o phy ase hyd olysable P in NaOH and ci a e-bica bona e
ex ac s ( NaOH
h
+CB
h
)inhigh-Psamples
P
CaCl2
TV Clay pH Phospha ase O ganic C ACCE Feca + Fed Feca/Fed PBC
1
CB
h
NaOH
h
+CB
h
Olsen P TV 0.63*** −0.82*** −0.76*** 0.26 ns 0.11 ns −0.31 ns −0.55* 0.42 ns −0.74*** 0.11 ns 0.32 ns
P
CaCl2
TV −0.80*** −0.61** −0.33 ns −0.18 ns −0.54* 0.28 ns 0.68** −0.67** 0.25 ns 0.77***
Clay −0.60** 0.52* −0.31 ns −0.44 ns 0.52* −0.66** 0.85*** −0.25 ns 0.69**
pH 0.41 ns 0.17 ns 0.71** 0.19 ns −0.73** 0.57* 0.27 ns 0.2 ns
Phospha ase 0.39 ns 0.28 ns 0.23 ns 0.29 ns 0.52* −0.36 ns −0.48*
O ganic C −0.14 ns 0.1 ns 0.12 ns −0.23 ns 0.23 ns 0.17 ns
ACCE −0.59** −0.70** 0.34 ns −0.02 ns −0.35 ns
Feca + Fed −0.35 ns 0.50* 0.23 ns 0.44 ns
Feca/Fed −0.46* −0.24 ns 0.55*
PBC
1
0.13 ns −0.42 ns
CB
h
0.77***
ns no signi ican
*P < 0.05; **P < 0.01; ***P < 0.001
Fig. 1 Po s a a ion expe imen :
asun lowe in g owing chambe
wi h bincipien P de iciency
symp oms and cclea de iciency
symp oms and dwhea wi h eP
de iciency symp oms
Ag on. Sus ain. De . (2016) 36: 54 Page 5 o 8 54

solid phase a he same amoun o so bed P wi h inc easing a io
o poo ly o highly c ys alline Fe oxides. Thus, he ype o so -
ben su aces was also a ele an p ope y a ec ing h eshold
alues.
Phospho us bu e capaci y es ima ed a 1 mg l
−1
seems a
c ucial p ope y explaining a iabili y in h eshold alues o
OlsenPandP
CaCl2
. This is in ag eemen wi h he cu en s age
o knowledge (Hol o d 1980; Bolland e al. 1994;Ehle e al.
2003). Signi icance o soil P bu e capaci y in ou long- e m
deple ion expe imen o explaining h eshold alues o
Olsen P was much g ea e han ha obse ed by Recena
e al. (2015) o explaining he a io o plan P up ake o
Olsen P when P a ailabili y in g owing media was sca ce.
This e eals ha P bu e capaci y may be c ucial o poin o
he le el o P in soil a which he e is no limi a ion in P up ake
by plan s, bu no so ele an in explaining he P up ake by
plan s below his le el.
Phy ase hyd olysable P in NaOH and ci a e-
bica bona e ex ac s was signi ican in explaining he
Th eshold alues o Olsen P (mg kg-1)
2
4
6
8
10
12
14
16
18
Es ima ed h eshold alues o Olsen P (m
g
k
g
-1)
2 4 6 8 10 12 14 16 18
246810121416
Th eshold alues o Olsen P (mg kg-1)
2
4
6
8
10
12
14
16
18
b
a
Fig. 2 Es ima ion h eshold Olsen P alues o e ilize esponse as a
unc ion o aclay, pH, and mean phospha ase ac i i y in he hizosphe e
(mean o he ou c ops in high-P samples); Y = 32 −0.015 clay −3.26
pH + 0.05 phospha ase; R
2
=0.87;P< 0.001; and coe icien s o each
explica i e a iable signi ican a P< 0.05 in he leas signi ican case and
bclay, soil o ganic ca bon (SOC), and phy ase hyd olysable P in CB
ex ac s o high-P samples (CB
h
); Y = 14 + 2.05 SOC −0.22
CBh −0.02 clay; R
2
=0.75;P< 0.001; and coe icien s o each
explica i e a iable signi ican a P< 0.1 in he leas signi ican case.
Th eshold alue can be es ima ed also as a unc ion o clay and pH 36–
0.012 clay—3.02 pH; R
2
= 0.81; P < 0.001; and coe icien s o each
explica i e a iable signi ican a P< 0.01 in he leas signi ican case and
mean absolu e e o = 1.12
Th eshold alues o PCaCl2 (mg L-1)
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
Es ima ed h eshold alue o PCaCl2 (mg L-1)
-2,5 -2,0 -1,5 -1,0
-2,5 -2,0 -1,5 -1,0
Th eshold alue o PCaCl2 (mg L-1)
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
b
a
Fig. 3 Es ima ion o he loga i hm o he h eshold P
CaCl2
alues o
e ilize esponse as a unc ion o aclay and he a io o Fe
ca
o Fe
d
,
Y=−2.02 −0.0018 clay + 2.92 Fe
ca
/Fe
d
,R
2
=0.57,P< 0.001, and
coe icien s o each explica i e a iable signi ican a P<0.05inbo h
cases and bpH and he sum o phy ase hyd olysable in NaOH and CB
ex ac s, Y = 2.38 −0.62 pH + 0.034 (NaOH
h
+CB
h
), R
2
= 0.54,
P< 0.01, and coe icien s o each explica i e a iable signi ican a
P< 0.05 in bo h cases. Th eshold alue can be also es ima ed as a
unc ion o clay and ac i e Ca ca bona e equi alen (ACCE),
Y=−1.13 −0.039 ACCE −0.002 clay. R
2
= 0.56, P< 0.01, and
coe icien s o each explica i e a iable signi ican a P<0.05
54 Page 6 o 8 Ag on. Sus ain. De . (2016) 36: 54
h eshold alues o bo h soil P es s when he alue conside ed
was ha a he beginning o he deple ion expe imen o he
high-P samples (Fig. 2b and Fig. 3b). In addi ion, phospha ase
was signi ican explaining Olsen P h eshold alues when he
mean ac i i y o he ou deple ion s eps in ol ing high-P sam-
ples was aken in o accoun . This con ibu ion o o ganic P o P
supply o plan s was p e iously e idenced by Recena e al.
(2015) when he a ailable P in he g owing media was e y
low in a sho - e m P deple ion expe imen . Howe e , ou
long- e m P deple ion expe imen e ealed ha o ganic P also
a ec s he soil P es alue abo e which plan s can ake up P
wi hou dec ease in yield. The p esen esul s e eal ha he
signi ican in luence o o ganic P- ela ed ac o s on h eshold
alues o p ac ical use o Olsen P as soil P es in assessing P
e iliza ion. Mo eo e , he con ibu ion o o ganic P o P up ake
by plan s was no es ic ed o s a a ion in ino ganic a ailable P
as p e iously obse ed (Recena e al. 2015); i seemed o be mo e
ela ed o o ganic P o ms a ailable o enzyma ic hyd olysis in
he hizosphe e.
O ganic ca bon in soil also seems o con ibu e o
explain Olsen P h eshold alues (Fig. 2b). I is well
known ha dissol ed o ganic ma e a ec s he equilib-
ium o P in soil h ough compe i ion wi h phospha e
o he so ben su aces and inhibi ion o me al phos-
pha e p ecipi a ion (Delgado e al. 2002; Saa ed a
e al. 2007). In addi ion, inc eased o ganic ca bon in
soils esul ing om o ganic ma e addi ion can p omo e
a dec ease in soil P bu e capaci y (Sui and Thompson
2000) which also con ibu es o explain po en ial e ec s
o soil o ganic ca bon on soil P es h eshold alues.
When compa ed wi h he cu en s age o knowledge,
he p esen wo k p o ides a mo e comple e iew o soil
ac o s a ec ing he de ini ion o h eshold alues o
Olsen P and P in soil solu ion, as es ima ed, e.g., by ex-
ac ion wi h 0.01 M CaCl
2
. This was achie ed by a deep
analysis o he soil p ope ies in ol ed in P dynamics.
F om hese esul s, new single models o es ima e h esh-
old alues based on ou inely de e mined soil p ope ies
can be p oposed. In he case o Olsen P, a model based on
clay and pH explains 81 % o he a ia ion wi h an es i-
ma ed mean absolu e e o o 1.12. This in p ac ical e ms
does no ha e a ele an economical impac in assessing P
e iliza ion. De elopmen o hese models should be pe -
o med, o p ac ical ecommenda ions, a ield scale and
o di e en c ops because ac o s a ec ing oo de elop-
men and he po en ial con ibu ion o subsu ace ho izons
a e ele an o he supply o P o c ops. Ou esul s go
beyond he p e ious ones o Recena e al. (2015), who
desc ibed he ele an ole o p ope ies ela ed o o ganic
P on P up ake by plan s. In ou case, o ganic P- ela ed
p ope ies a ec he le el o P in soil abo e which he
supply o P o he plan is assu ed, con ibu ing hus o
de ine h eshold alues o bo h soil P es s.
4Conclusions
Fac o s ela ed wi h he soil P bu e capaci y s and as he mos
ele an o explain he h eshold alues o bo h soil P es s.
Howe e , ac o s ela ed o o ganic P dynamics a e also in lu-
en ial on he alue o soil P es in soil abo e which he e is a
su icien P supply o plan s hus con ibu ing o de ine h esh-
old alues o bo h soil P es s. In p ac ice, de ini ion o accu-
a e h eshold alues o Olsen P in soils o Medi e anean
egions should p o i om wo basic soil p ope ies, namely,
clay con en and pH. In a simple manne , his could be
achie ed by de ining di e en anges o h eshold alues de-
pending on he clay con en and pH o soil.
Acknowledgmen s This s udy was unded by he Spanish Minis y o
Science and Inno a ion and he Eu opean Regional De elopmen Fund o
he Eu opean Union h ough he Na ional Resea ch, De elopmen and
Inno a ion P og am (Plan Nacional I + d + i, AGL2011-29893-CO2-01,
and AGL2011-29893-CO2-02) and by he Regional Go e nmen o
Andalusia (P ojec AGR 63-85). M . Rami o Recena was a Ph.D. s uden
wi h a g an om he Regional Go e nmen . Fe ibe ia S.A. and OCA
Leb ija collabo a ed in he collec ion o soil samples o he p esen s udy.
Re e ences
Bai Z, Li H, Yang X, Zhou B, Shi X, Wang B, Li D, Shen J, Chen Q, Qin
W, Oenema O, Zhang F (2013) The c i ical soil P le els o c op
yield, soil e ili y, and en i onmen al sa e y in di e en soil ypes.
Plan Soil 372:27–37. doi:10.1007/s11104-013-1696-y
Bolland MDA, Wilson IR, Allen DG (1994) E ec o P bu e capaci y
and P e en ion index o soils on soil es P, soil es P calib a ions
and yield esponse cu a u e. Aus J Soil Res 32:503–517.
doi:10.1071/SR9940503
Ca e RB, Nelson LA (1971) A simple s a is ical p ocedu e o pa i ioning
soil es co ela ion da a in o wo classes. Soil Sci Soc Am P oc 35:
658–660. doi:10.2136/sssaj1971.03615995003500040048x
Colombo C, Ba ón V, To en J (1994) Phospha e adso p ion and deso p-
ion in ela ion o mo phology and c ys al p ope ies o syn he ic
hema i es. Geochim Cosmochim Ac a 58:1261–1269. doi:10.1016
/0016-7037(94)90380-8
Colomb B, Debaeke P, Jouany C, Nolo JM (2007) Phospho us manage-
men in low inpu s ockless c opping sys ems: c op and soil e-
sponses o con as ing P egimes in a 36-yea expe imen in sou he n
F ance. Eu J Ag on 26:154–165. doi:10.1016/j.eja.2006.09.004
Co dell D, Nese TS (2014) Phospho us ulne abili y: a quali a i e
amewo k o assessing he ulne abili y o na ional and egional
ood sys ems o he mul i-dimensional s esso s o phospho us sca -
ci y. Glob En i on Chang 24:108–122. doi:10.1016/j.
gloen cha.2013.11.005
Co dell D, D ange JO, Whi e S (2009) The s o y o phospho us: global
ood secu i y and ood o hough . Glob En i on Chang 19:292–
305. doi:10.1016/j.gloen cha.2008.10.009
Delgado A, To en J (1997) Phospha e ich soils in he Eu opean Union:
es ima ing o al plan -a ailable phospho us. Eu J Ag on 6:205–214.
doi:10.1016/S1161-0301(96)02048-5
Delgado A, Mad id A, Kasem S, And eu L, del Campillo MC (2002)
Phospho us e ilize eco e y om calca eous soils amended wi h
humic and ul ic acids. Plan Soil 245:277–286. doi:10.1023
/A:1020445710584
Ag on. Sus ain. De . (2016) 36: 54 Page 7 o 8 54
Delgado A, Scalenghe R (2008) Aspec s o phospho us ans e om
soils in Eu ope. J Plan Nu Soil Sci 171(4):552–575. doi:10.1002
/jpln.200625052
Delgado A, del Campillo MC, To en J (2010) Limi a ions o he Olsen
me hod o assess a ailable phospho us in eclaimed ma sh soils. Soil
Use Manage 26:133–140. doi:10.1111/j.1475-2743.2010.00264.x
Ehle P, Mo el C, Fo yma M, Des ain JP (2003) Po en ial ole o phos-
pha e bu e ing capaci y o soils in e ilize managemen s a egies
i ed o en i onmen al goals. J Plan Nu Soil Sci 166:409–415.
doi:10.1002/jpln.200321182
Geng X, Guilla d K, Mo is TF (2014) Rela ing u g ass g ow h and
quali y o equen ly measu ed soil ni a e. C op Sci 54:366–382.
doi:10.2135/c opsci2013.03.0145
Hol o d ICR (1980) E ec s o phospha e bu e capaci y on c i ical le els
and ela ionships be ween soil es s and labile phospha e in whea
g owing soils. Aus J Soil Res 18:405–414. doi:10.1071
/SR9800405
Keyze M (2010) Towa ds a closed phospho us cycle. De Economis 158:
411–425. doi:10.1007/s10645-010-9150-5
Kulhánek M, Balík J, Če ný J, Ned ěd KB (2007) The in luence o
di e en in ensi ies o phospho us e ilizing on a ailable phospho-
us con en s in soils and up ake by plan s. Plan Soil En i on 53:
382–387
Malla ino AP, Blackme AM (1992) Compa ison o me hods o de e min-
ing c i ical concen a ions o soil es phospho us o co n. Ag on J
84:850–856. doi:10.2134/ag onj1992.00021962008400050017x
Mu phy J, Riley JP (1962) A modi ied single solu ion me hod o he
de e mina ion o phospha e in na u al wa e s. Anal Chim Ac a 27:
31–36. doi:10.1016/S0003-2670(00)88444-5
Ney oud JA, Lische P (2003) Do di e en me hods used o es ima e soil
phospho us a ailabili y ac oss Eu ope gi e compa able esul s? J
Plan Nu Soil Sci 266:422–431. doi:10.1002/jpln.200321152
Olsen SR, Cole CV, Wa anabe FS, Dean LA (1954) Es ima ion o a ail-
able phospho us in soils by ex ac ion wi h sodium bica bona e.
USDA ci cula 939. US Go e nmen P in ing O ice, Washing on
DC
Ryan J, Ib ikci H, Delgado A, To en J, Somme R, Rashid A (2012)
Signi icance o phospho us o ag icul u e and he en i onmen in
he Wes Asia and No h A ica egion. Ad Ag on 114:91–153.
doi:10.1016/B978-0-12-394275-3.00004-3
Recena R, To en J, del Campillo MC, Delgado A (2015) Accu acy o
Olsen P o assess plan P up ake in ela ion o soil p ope ies and P
o ms. Ag on Sus ain De 35:1571–1579. doi:10.1007/s13593-015-
0332-z
Saa ed a C, Velasco J, Pajuelo P, Pe ea F, Delgado A (2007) E ec s
o illage on phospho us elease po en ial in a SpanishVe isol. Soil
Sci Soc Am J 71:56–63. doi:10.2136/sssaj2006.0162
Sánchez-Alcalá I, del Campillo MC, Ba ón V, To en J (2014) The
Olsen P/solu ion P ela ionship as a ec ed by soil p ope ies. Soil
Use Manage 30:454–462. doi:10.1111/sum.12141
Sánchez-Alcalá I, Campillo MC, To en J (2015) C i ical Olsen P and
CaCl
2
-P le els ela ed o soil p ope ies: esul s om mic opo ex-
pe imen s. Soil Use Manage. doi:10.1111/sum.12184
San ne J, Mannel M, Bu ell LD, Hoe e C, K euzede A, Wenzel WW
(2015) Phospho us up ake by Zea mays L. Is quan i a i ely p edic -
ed by in ini e sink ex ac ion o soil P. Plan Soil 386:371–383.
doi:10.1007/s11104-014-2271-x
Sch öde JJ, Smi AL, Co dell D, Rosema in A (2011) Imp o ed phos-
pho us use e iciency in ag icul u e: a key equi emen o i s sus-
ainable use. Chemosphe e 84:822–831. doi:10.1016/j.
chemosphe e.2011.01.065
Shi ani M, Sha ia mada i H, Kalbasi M (2005) Phospho us bu e ing
capaci y indices as ela ed o soil p ope ies and plan up ake. J. Plan
Nu 28:537–550. doi:10.1081/PLN-200049235
Soil Su ey S a (2010) Keys o soil axonomy, 11 h edn. USDA-Na u al
Resou ces Conse a ion Se ice, Washing on, DC
Sui Y, Thompson ML (2000) Phospho us so p ion, deso p ion, and bu -
e ing capaci y in a biosolids-amended mollisol. Soil Sci Soc Am J
64:164–169. doi:10.2136/sssaj2000.641164x
Tandy S, Mundus S, Yng esson J, de Bang TC, Lombi E, Schjoe ing JK,
Hus ed S (2011) The use o DGT o p edic ion o plan a ailable
coppe , zinc and phospho us in ag icul u al soils. Plan Soil 346:
167–180. doi:10.1007/s11104-011-0806-y
Tang X, Ma Y, Hao X, Li X, Li J, Huang S, Yang X (2009) De e mining
c i ical alues o soil Olsen-P o maize and win e whea om long-
e m expe imen s in China. Plan Soil 323:143–151. doi:10.1007
/s11104-009-9919-y
Van Vuu en DP, Bouwman AF, Beusen AHW (2010) Phospho us de-
mand o he 1970–2100 pe iod: a scena io analysis o esou ce
deple ion. Glob En i on Chang 20:428–439. doi:10.1016/j.
gloen cha.2010.04.004
Wi he s PJ, Neal C, Ja ie HP, Doody DG (2014) Ag icul u e and eu o-
phica ion: whe e do we go om he e? Sus ainabili y 6:5853–5875.
doi:10.3390/su6095853
54 Page 8 o 8 Ag on. Sus ain. De . (2016) 36: 54