Soil nu ien s oichiome y impac s on soil o ganic ca bon s ocks in
long- e m phospho us e ilisa ion expe imen s
Pa ag Bhople
a,*
, Da id Wall
a
, Ka l Richa ds
a
, Timo hy Clough
b
, Fiona B ennan
a
,
Ga y Lanigan
a
, Ma Ros
c
, Anke M. He mann
d
, Ingebo g F. Pede sen
e
, La s Elsgaa d
e
,
Naoise Nunan
e,
, Ch is oph Mülle
g,h,i
, K is ina Kleineidam
g
, Se gio E. Mo ales
j,k
,
Daniel Goll
l
, Giulia Bondi
a
a
C ops En i onmen and Land Use Depa men , Teagasc, Johns own Cas le, Y35 TC97 Wex o d, I eland
b
Depa men o Soil and Physical Sciences, Lincoln Uni e si y, Lincoln 7647 Ch is chu ch, New Zealand
c
Wageningen En i onmen al Resea ch, Wageningen Uni e si y & Resea ch, PO Box 47, 6700 AA Wageningen, he Ne he lands
d
Swedish Uni e si y o Ag icul u al Sciences, Depa men o Soil and En i onmen , PO Box 7014, SE-750 07 Uppsala, Sweden
e
Depa men o Ag oecology, Aa hus Uni e si y, Bliche s Alle 20, DK-8830 Tjele, Denma k
Ins i u e o Ecology and En i onmen al Sciences, CNRS-So bonne Uni e si ´
e-IRD-UPEC-P7-INRA, Pa is, F ance
g
Ins i u e o Plan Ecology (IFZ), Jus us Liebig Uni e si y Giessen, Hein ich-Bu -Ring 26, 35392 Giessen, Ge many
h
School o Biology and En i onmen al Science and Ea h Ins i u e, Uni e si y College Dublin, Dublin 4 Bel ield, I eland
i
Liebig Cen e o Ag oecology and Clima e Impac Resea ch, Jus us Liebig Uni e si y Giessen, Ge many
j
Depa men o Mic obiology & Immunology, Uni e si y o O ago, 720 Cumbe land S ee , PO Box 56, 9054 Dunedin, New Zealand
k
MPG Ranch, Flo ence, MT 59833, USA
l
Uni e si ´
e Pa is Saclay, CEA-CNRS-UVSQ, LSCE/IPSL, Gi -su -Y e e, F ance
ARTICLE INFO
Handling Edi o : D . And ew Ma geno
Keywo ds:
Soil ca bon s o age
C:N:P s oichiome y
Long- e m ield expe imen s
Ag oecosys ems managemen
Clima e change
ABSTRACT
Managing ag oecosys ems o enhance soil o ganic ca bon (SOC) s o age is impo an o mi iga ing clima e
change. Howe e , he ans o ma ion o SOC is in ima ely connec ed o nu ien cycling, pa icula ly ni ogen
(N) and phospho us (P). While P cons ain s on plan g ow h a e known, hei e ec s on ca bon (C) and N cycling
emain unce ain. The s udy uses se e al long- e m expe imen s (LTEs) o de e mine he impo ance o N-P
in e ac ions and he op imal C:N:P s oichiome y o long- e m SOC s ocks in managed ag icul u al sys ems. The
aim was o de e mine he in luence o mul i-decadal P e ilisa ion on SOC s ocks and s oichiome ic in e ac ions
o C, N and P in ag icul u al soils (up o 50 cm) ac oss di e en soil ex u al classes and land uses. Fo his, he
soils we e sampled a h ee dep hs 0–10, 10–30 and 30–50 cm om six LTEs in Eu ope ( h ee g asslands and
h ee a ables) o de e mine soil physico-chemical p ope ies. The esul s showed compa able SOC s ocks in
con as ing P ea men s ac oss land uses. In g asslands, SOC s ocks a 0–50 cm dep h anged om 9.7 o 40.6 C
ha
−1
while in a able si es, hey we e be ween 11.0 and 48.3 C ha
−1
. The SOC s ocks did no a y signi ican ly
ac oss P ea men s indica ing ha long- e m P e ilisa ion did no a ec C s o age. G assland si es had highe
SOC s ocks in he 0–10 cm, while a a able si es hey we e highe a 10–30 cm dep hs. The maximum p edic ed
SOC s ock o 30.9 C ha
−1
was wi h SOC/TN ( o al ni ogen) a io o 10.1 and SOC/TP ( o al phospho us) a io o
32.6 in g assland si es, while hese a ios we e 10.9 and 29.4, espec i ely, in a able si es, whe e he p edic ed
maximum SOC s ock was 33.3 C ha
−1
. O e all, he s udy shows ha he long- e m phospho us e ilisa ion o
g assland and a able soils did no a ec SOC s ocks a he s udied LTEs.
1. In oduc ion
In he e es ial biosphe e, soils a e he la ges ese oi o ca bon
(C) and ag oecosys ems unc ion as one o he mos impo an C sinks
(Lal, 2018). Cap u ing a mosphe ic CO
2
ia plan pho osyn hesis and
s o ing o ganic C in soils can mi iga e a mosphe ic g eenhouse gas
concen a ions and con ibu e o clima e egula ion (Coonan e al.,
2019). Howe e , he bene i s o soil o ganic ca bon (SOC) seques a ion
* Co esponding au ho a : Teagasc, C ops En i onmen and Land Use Depa men , Johns own Cas le, Wex o d Y35 TC97, I eland.
E-mail add ess: [email p o ec ed] (P. Bhople).
Con en s lis s a ailable a ScienceDi ec
Geode ma
jou nal homepage: www.else ie .com/loca e/geode ma
h ps://doi.o g/10.1016/j.geode ma.2025.117538
Recei ed 7 Ma ch 2025; Recei ed in e ised o m 11 Sep embe 2025; Accep ed 1 Oc obe 2025
Geode ma 463 (2025) 117538
A ailable online 29 Oc obe 2025
0016-7061/© 2025 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY license (
h p://c ea i ecommons.o g/licenses/by/4.0/ ).
go beyond educing a mosphe ic CO
2
concen a ions alone. Seques-
e ing mo e C in soils as soil o ganic ma e (SOM) con ibu es o
enhancing soil s uc u e by os e ing agg ega e o ma ion, inc easing
po osi y, inc easing soil s abili y and ca ion exchange capaci y, along
wi h imp o ed wa e in il a ion and e en ion (Lal, 2018). These
physico-chemical imp o emen s enable soils o e ain nu ien s essen ial
o plan g ow h while he enhanced SOM also suppo s di e se soil
mic obial communi ies, which play a i al ole in nu ien cycling and
o ganic ma e decomposi ion (Ki kby e al., 2011). Howe e , se e al
ac o s, such as he clima e, soil ype and land use change, can in luence
he p ocess o C seques a ion in ag oecosys ems (Lal, 2018). Fu he -
mo e, managemen p ac ices ela ed o e ilise use, esidue inpu s, and
illage in ensi y also a ec C seques a ion (Lal, 2018; S ockmann e al.,
2015).
Soil C seques a ion is closely linked o he cycling o ni ogen (N)
and phospho us (P), which a e he main nu ien s in he soil ha
egula e plan p oduc i i y and mic obial ac i i y. Fu he mo e, he
s oichiome ic a ios o C, N and P (C:N:P a io) in luence he o ma ion
o SOM (Ki kby e al., 2014). An op imal balance o hese elemen s is
he e o e c ucial o main aining soil e ili y and he long- e m s o age
o C. The a ailabili y o P has a c ucial impac on soil C dynamics (Ki kby
e al., 2014), pa icula ly when i is a limi ing nu ien (Spohn, 2020).
Howe e , ele a ed P le els may also be associa ed wi h an inc ease in
mic obial biomass and espi a ion (Spohn and Schleuss, 2019), which
accele a e he decomposi ion o SOM and po en ially o se C seques-
a ion by eleasing CO
2
back in o he a mosphe e (Ki kby e al., 2014;
Coonan e al., 2019). This dual ole o P in p omo ing SOM build-up and
mine alisa ion highligh s he complexi y o in e ac ions be ween
nu ien -d i en p oduc i i y and SOC pe sis ence in soils.
Long- e m P e ilisa ion expe imen s (LTEs) o e he possibili y o
s udy he dis inc ela ionships be ween P, N and soil C dynamics. Fo
example, in he Eu opean con ex , mode a e P inpu s (20–30 kg P ha
−1
y
−1
) ha e been shown o enhance p oduc i i y, while excess P (>50 kg
P ha
−1
y
−1
) inc eased SOM decomposi ion ia mic obial espi a ion in
g assland soils in I eland (G aça e al., 2022). I is impo an o no e ha
sho - e m p iming e ec s do no necessa ily ansla e in o highe long-
e m ne SOM decomposi ion. Ano he I ish LTE demons a ed ha
o ganic P inpu s s imula ed mic obial ac i i y, leading o enhanced N
mine aliza ion and sho - e m posi i e p iming esponses. Howe e ,
o e he long e m, hese ea men s esul ed in lowe ne SOM
decomposi ion compa ed wi h ino ganic P inpu s, which showed nega-
i e p iming e ec s (Kelly, 2022). In a g assland s udy in he
Ne he lands, abundan N and con inuous P en ichmen s imula ed mi-
c obial ac i i y esul ing in highe SOM u no e (Reijne eld e al.,
2009). Con e sely, LTEs in a able lands in Sweden showed ha mod-
e a e P and N inpu suppo ed plan g ow h and slowe SOM decom-
posi ion, while addi ional P (>40 kg P ha
−1
y
−1
) ampli ied p iming
e ec s and SOM loss in p esence o high N con en s in soils (Be gk is
e al., 2011). In a Danish a able si e unde P and N inpu s, SOC s ocks
dec eased due o inc eased mic obial biomass and espi a ion a es
(Liang e al., 2019). Simila e ec s a e also ound ou side o Eu ope. Fo
example, a g azed pas u e LTE s udy in New Zealand ound ha mod-
e a e P a es (20–30 kg P ha
−1
y
−1
) esul ed in mo e s able SOM, bu
ha excess P esul ed in a ne loss o C om soils (Cond on and Goh,
1989).
Al hough he unde s anding o in e ac ions be ween nu ien s (C, N
and P) in opsoils has p og essed, less is known abou he p ocesses in
subsoils. The dis ibu ion o N a ies h oughou he soil p o ile
depending on N inpu s om e ilise and esidues, as well as p ocesses
such as N deposi ion, decomposi ion o li e , mic obial N ixa ion,
leaching and deni i ica ion (Chen e al., 2014; Rumpel e al., 2015;
Peixo o e al., 2021). Mo eo e , due o limi ed oo ac i i y, educed
mic obial biomass and hizodeposi ion, soil e ili y usually dec eases
wi h inc easing dep h, as indica ed by highe soil C/N a ios (Ki kby
e al., 2011; Bhople e al., 2019, Liang e al., 2019). The a ailabili y o P
in ag icul u al soils s ongly depends on i s p esence in soil mine als and
i s adso p ion o eac i e su aces in soil (G aça e al., 2022). Mos o he
mic obial and plan ac i i y is concen a ed in opsoils, associa ed wi h
eadily a ailable labile P pools. In subsoils, ex ending below 30 cm
dep h, P mobili y and a ailabili y dec eases due o s onge adso p ion
o soil pa icles leading o P s a i ica ion h oughou he soil p o ile in
combina ion wi h changes in soil pH de e mining he bioa ailabili y o P
in soils (Lo enz and Lal, 2005; Rumpel e al., 2015; Liang e al., 2019;
G aça e al., 2022). Fu he mo e, he s oichiome ic a io o soil C:N:P is
no cons an wi h soil dep h making he ole o P in sub-soil C seques-
a ion unclea . In his ega d, long- e m P e ilise expe imen s ha e
Table 1
Long- e m expe imen al si es (LTEs) in ol ed in he s udy and hei main cha ac e is ics.
Coun y I eland The Ne he lands Sweden Denma k
Ins i u e Teagasc Wageningen
Uni e si y
Swedish Uni e si y o Ag icul u al Sciences Aa hus Uni e si y
T ial name Cowlands (JC1) Dai y-cu (JC2) Lelys ad (LE) Lanna Ska a 1 (LS1) Lanna Ska a 2 (LS2) Jynde ad (JY)
Land Use G assland G assland G assland A able A able A able
Soil dis u bance G azing egime silage Combina ion o
silage and
o a ional g azing
C op o a ion,
annual in e sion
illage
C op o a ion,
annual in e sion
illage
Annual ploughing
Loca ion 52.3058 N 52.2979 N 52.52 N 59.8761 N 59.8761 N 54.8896 N
6.5080 W 6.4994 W 5.55 E 17.9533 E 17.9533 E 9.1276 E
Yea o s a 1968 1995 1989 1936 1941 1944 (liming 1942)
Soil ype- ex u al class Humic Gleysol −
Sandy clay loam
S agnic Cambisol
−Clay loam
Gleyic Fu isol
Clay
Ude ic Haplobo oll
(USDA Soil;
Taxonomy) – Sil
clay loam
Ude ic Haplobo oll
(USDA Soil;
Taxonomy) – Sil
clay loam
O hic Haplohumod
−Coa se sand
Phospho us (P) e ilise Calcium
supe phospha e
T iple
supe phospha e
Ca le manu e +
Supe phospha e
Supe phospha e Supe phospha e Supe phospha e
(un il 2012) and
subsequen ly as
T iple
supe phospha e
P e ilise managemen One applica ion
annually
One applica ion
annually
Two applica ions
annually
One applica ion
e e y six h yea
One applica ion
e e y six h yea .
One applica ion
annually
P ea men s Low High Low High Low High Low High Low High Low High
P a es (kg ha
−1
) 0 30 0 45 23 41 0 105 0 105 0 15.6
P Mo gan (mg L
-1
) 1.19 6.47 1.82 4.63 12.30 20.47 0.81 1.62 0.62 1.11 2.10 12.48
Typical a e age c op yield (kg DM ha
−1
) 3831 3785 4060 4540 9888 10,952 5484 6731 3266 5461 3674 4340
P con en s o ha es ed biomass
(g P kg
−1
DM)
2.9 3.5 2.7 3.2 3.5 3.5 3.1 3.9 3.1 3.9 3.0 3.3
P. Bhople e al.
Geode ma 463 (2025) 117538
2
demons a ed ha P addi ion can inc ease labile P (based on he Olsen P
index) in opsoil unde g azed pas u e managemen , while in subsoils P
emained igh ly bound o mine al su aces he eby educing i s a ail-
abili y in ee o m (Coonan e al., 2019; Reijne eld e al., 2009).
The N and P a ailabili y co-limi s C mine alisa ion in deepe soils
whe e he C/P a io is also highe (Peixo o e al., 2021). High C/P a io
may cause mic obes o immobilise P, while simul aneously, low N
a ailabili y can limi mic obial ac i i y making bo h N and P co-limi ing
ac o s o C mine alisa ion in deepe soils. Con e sely, wi h a low C/P
a io, he mine alisa ion o o ganic P seems o be s imula ed, inc easing
P a ailabili y in soils and simul aneously accele a ing bo h he mic obial
decomposi ion o SOM and he me abolic u ilisa ion o C and P (Fon aine
e al., 2007; Ki kby e al., 2014; Peixo o e al., 2021). Al hough subsoils
a e c i ical long- e m sinks o C (Coonan e al., 2019), he SOC s ock
changes as a unc ion o dep hs and he po en ial in e ac ions wi h o he
nu ien a ios emain poo ly explo ed, highligh ing he need o an
in eg a ed app oach o s udying soil nu ien s and how hei s oichio-
me ic a ios in luence he C s o age po en ial o soils.
The cu en s udy in es iga es he dis ibu ion o SOC s ocks and C:
N:P s oichiome y in soil p o iles om six long- e m expe imen al si es
(LTEs) in Eu ope. The six LTEs ep esen dis inc phospho us (P) e il-
isa ion le els (high and low) and wo land use ypes (g asslands and
a able). The use o LTEs and associa ed P legacy da a a e use ul o
in es iga ing C s o age dynamics in esponse o long- e m P inpu s as
well as o explo e opsoil and sub-soil SOC s o age po en ial (Lo enz and
Lal, 2005; Kell, 2011; Lynch and Wojciechowski, 2015). We es ed he
ollowing hypo heses: 1) The long- e m P e ilisa ion inpu s in luence
SOC s ocks ac oss soil dep hs, wi h highe P e ilisa ion leading o
g ea e accumula ion o SOC compa ed o he low P inpu s; 2) The
a ia ions in SOC s ocks a e associa ed wi h soil C:N:P s oichiome y,
e lec ing po en ial in e ac ions among C, N and P in s udied ag o-
ecosys ems. The speci ic objec i e o he s udy was o e alua e he e -
ec s o long- e m P e ilisa ion egimes on SOC s ocks and o examine
hei ela ionships wi h soil C:N:P s oichiome y ac oss di e en land-
uses and soil dep hs.
2. Ma e ials and me hods
2.1. The long- e m expe imen al si es and P managemen
This s udy was ca ied ou using LTEs in Eu ope wi h con as ing P
e ilise ea men s ha ha e been unning con inuously o 29–89
yea s (Table 1). The LTEs co e ed six ield si es loca ed in I eland (JC1,
JC2), The Ne he lands (LE), Sweden (LS1, LS2) and Denma k (JY). All
si es a e in he cool empe a e clima ic zone o he No he n hemisphe e.
The LTEs included h ee g assland si es (JC1, JC2, LE) and h ee a able
si es (LS1, LS2, JY). The g assland si es we e subjec ed o g azing only,
cu ing only o a combina ion o bo h. Soil ex u e a he g assland si es
anged om sandy clay loam o clay. The a able si es we e illed
in e sely o ploughed annually, and he soil ex u e anged om coa se
sand (JY) o hea y clay soils (LS1 and LS2).
The LTEs ha e been subjec ed o con olled P e ilise applica ions.
A si e JC1 and JC2, calcium supe phospha e and iple supe phospha e
we e applied as P e ilise s wi h one applica ion pe yea gene ally in
ea ly sp ing. The e we e also P e u ns h ough g azing a JC1. A he LE
si e, a combina ion o ca le manu e and supe phospha e was applied
wice pe yea , in ea ly sp ing and a e e e y ha es . A high dose o P
e ilise was applied e e y six h yea a si es LS1 and LS2, while a he
JY si e, mine al P e ilise was applied once pe yea as supe phospha e
un il 2012 and subsequen ly as iple supe phospha e.
In his s udy, we ha e used o al P (TP) as an indica o o legacy P
accumula ion om long- e m P e ilisa ion inpu s, o p o ide a
consis en measu e o c oss-si es compa ison in he LTEs. Two P le els
we e selec ed om each si e we e ca ego ized nominally as low and high
P. In ou s udy, he ‘low’ and ‘high’ P also e e s o he P con en o he
soil a he han he amendmen s. A all si es, he low P applica ion
consis ed o ze o P (0 kg ha
−1
) excep a he LE g assland si e whe e he
low P applica ion was 23 kg ha
−1
y
−1
. The high P applica ion a e
a ied ac oss di e en LTEs (Table 1) due o he expe imen al designs,
di e ences in soil ypes and he P equi emen s o plan g ow h. A he
h ee g assland si es (JC1, JC2 and LE), he high P applica ion consis ed
o 30, 45 and 41 kg ha
−1
y
−1
espec i ely. A he h ee a able si es, he
high P applica ion consis ed o 105 kg ha
−1
applied e e y 6 h yea a he
LS1 and LS2 si es, and 15.6 kg ha
−1
y
−1
o JY. The JY si e also ecei ed
one applica ion o 156 and 263 kg P ha
−1
in 1944 and 1972, espec i ely
o imp o e hei o e all P s a us (Pede sen e al., 2025). A he JY si e
soils we e sampled in ea men plo s ecei ing highes liming a es o
12 Mg ha
−1
e e y 6 o 10 yea s. All P ea men s we e eplica ed h ee
imes ac oss he si es JC1, JC2 and JY. A si e LE, only one ea men
eplica e was a ailable and a LS1 and LS2 wo eplica es we e a ailable
o high and low P ea men s.
2.2. Soil sampling
Samples om he wo P e ilisa ion ea men s (high and low) we e
collec ed a he six LTEs in Sep embe 2022, wi hin each plo (30 m ×
30 m =900 m
2
size, excep o he JY si e whe e he plo a ea was 90 m
2
)
a ep esen a i e sampling a ea was selec ed. By acing he diagonals o
he sampling a ea, a soil pi (app ox. 60 ×60 ×60 cm) was exca a ed a
he iden i ied mid sampling poin . The p o ile ace in he pi was cleaned
wi h a kni e/ owel and a composi e sample o 500 g was aken om
h ee de ined dep hs, namely 0–10 cm, 10–30 cm and 30–50 cm. Wi hin
a plo , wo composi e samples we e pooled as a ep esen a i e o a
speci ic dep h and ea men . This esul ed in 84 soil samples in o al.
Soil samples o bulk densi y (BD) we e collec ed by inse ing s eel ings
(Ø 4.5 cm; heigh =4.5 cm) in o he soil a dep hs o 0–10, 10–30 and
30–50 cm o all P ea men eplica es.
2.3. Soil analyses
The composi e soil samples we e ans e ed o he labo a o y a-
cili ies in Teagasc Johns own Cas le, I eland. Roo s and s ones we e
emo ed om all soil samples. La e , he samples we e d ied a 40 ˚C and
sie ed (<2 mm mesh).
The soil pH was measu ed using deionised wa e (1:5 w/ ) as
desc ibed by G aça e al. (2022). A sub-sample o soil (0.2 g o d ied ball-
milled soil) was used o measu e soil o al ca bon (TC), o al ni ogen
(TN) and o al ino ganic ca bon (TIC) con en s using a T ueSpec C/N
analyse (LECO, USA). The SOC con en s we e calcula ed as he di e -
ence be ween TC and TIC. D ied soil (5 g) was used o Mo gan’s P
ex ac ion in a solu ion o 15 mL 0.62 M NaOH and 1.25 M CH
3
COOH
(pH 4.8). The soil solu ion was shaken o 30 min, be o e il e ing and
quan i ying on a spec opho ome e (Camspec, UK) o indica e he plan
a ailable P index (G aça e al., 2022). The Mehlich 3 ex ac ion was
pe o med using 20 mL Mehlich 3 eagen consis ing o 0.2 M
CH
3
COOH, 0.25 M NH
4
NO
3
, 0.015 M NH
4
F, 0.013 M HNO
3
and 0.001 M
EDTA and 2 g o d ied soil (Mehlich, 1984). The mix u e was shaken a
180 pm o 5 min and o al a ailable soil P was measu ed using
Induc i ely Coupled Plasma Op ical Emission Spec ome y (ICP-OES).
F om a 0.5 g d ied soil sample, he o al elemen s including P (TP) we e
measu ed using a e e se aqua egia diges ion me hod ollowed by
spec ome y measu emen o he diges a e (ISO 11466, 1995). In his
me hod deionised wa e (2 mL), HCl (37 %, 2.5 mL) and HNO
3
(69 %,
7.5 mL) we e added o he ube con aining he d ied soil sample and
placed in a diges e hea ed a 180 ◦C o 40 min. Upon cooling he
samples we e il e ed (Wha mann no. 42), be o e ICP–OES analysis.
In his s udy, he ole o P was cen al and he e o e we employed
mul iple app oaches o quan i y soil P. The plan -a ailable P o m was
de e mined using Mo gan’s and Mehlich-3 ex ac ions, which p o ide
indices o labile P o ms ele an o up ake by plan s. Fu he mo e, o al
P (TP) was measu ed using aqua egia diges ion ollowed by ICP-OES, as
a p oxy o cap u e bo h o ganic and mine al-bound P o ms. In his
P. Bhople e al.
Geode ma 463 (2025) 117538
3
s udy, TP was he e o e selec ed as he p incipal me ic o soil s oi-
chiome ic analysis conside ing ha i in eg a es he cumula i e impac s
o long- e m e ilisa ion and managemen on soil P s a us ac oss dep hs
and LTEs. While o ganic P (OP) is o en conside ed o be mo e di ec ly
associa ed wi h biological p ocesses, i also con ains bo h labile and
s able ac ions wi h a ying a ailabili y (Spohn, 2020; Ba ow e al.,
2021). Compa ed o his, TP consis s o bo h o ganic and ino ganic pools
and hus e lec s legacy P accumula ion due o long- e m e ilisa ion
inpu s (Ki kby e al., 2011; He e al., 2023). We indeed acknowledge ha
TP is no a di ec subs i u e o OP, especially when assessing e ec s o
sho - e m mic obial p ocesses and his ep esen s a limi a ion o ou
s udy. Ne e heless, TP p o ided an analy ically consis en and his o -
ically compa able measu e ac oss s udied LTEs, which allowed us o
e alua e cumula i e P en ichmen e ec s in ela ion o SOC s ock
changes (see Discussion o u he ca ea s L513-535).
The soil BD was calcula ed using d y weigh (d ying a 105 ◦C o
24–48 h) o he soil co e samples di ided by he olume o he soil co e.
The olume o s ones o >2-mm agmen s we e sub ac ed om he
o al soil co e olume o calcula e he olume o soil (Wal e e al.,
2016). Using he eco ded weigh s he BD (g cm
−3
) was calcula ed wi h
ollowing equa ion:
BD (g cm
−3
) =[(Ne DW −weigh o s ones −weigh o wooden
deb is)/(V −Vs −Vw)] (1)
Whe e, V is he inne olume o he soil BD ing (98.17 cm
3
), Vs is he
olume o >2 mm s ones (g o s ones/2.50 g cm
−3
(a g. densi y o
s ones) and Vw is he olume o >2 mm wooden deb is (b o wood/0.8 g
cm
−3
(a g. densi y o wood).
2.4. Calcula ions and s a is ical analysis
The SOC s ocks we e calcula ed as desc ibed in Necp´
alo ´
a e al.
(2014) and ep esen ed in C ha
−1
(Equa ion 2).
SOC s ocks ( C ha
−1
) =SOC concen a ion (mg C g
−1
d y soil) × ine
soil BD (g cm
−3
) ×Soil dep h ( hickness in cm) (2)
Two-way analysis o a iance (ANOVA) was ca ied ou on all sam-
ples wi h P ea men s as eplica es and used o de e mine whe he P
e ilise ea men s and soil dep hs had signi ican (p <0.05) e ec s pe
indi idual si e on: (i) soil physico-chemical p ope ies; and (ii) SOC
s ocks ( C ha
−1
). Tukey HSD pos -hoc es allowed mul iple compa ison
o means a 95 % con idence in e al, using R-package “mul comp”
(Ho ho n e al. 2008). The no mali y and he e oscedas ici y in da a we e
checked using esidual dis ibu ion and, i iola ed, da a we e log/Box-
Cox ans o med (R-package “MASS”; Ripley e al., 2011). Co ela ion
analyses we e conduc ed o de e mine he ela ionships be ween o al N
and P in he g assland and a able si es a bo h P le els, and be ween SOC
s ocks and o al N and P con en s in h ee soil dep hs o each land use.
P incipal componen analysis (PCA) was pe o med using he R-
package “ egan” (Oksanen, 2015). Two-way ANOVA was used o
es ing di e ences be ween dep hs and o he pa ame e s by log ans-
o ming he da a when equi ed. We i ed a polynomial eg ession (up
o he hi d deg ee) o model he non-linea ela ionships be ween he
p edic o a iables (SOC/TN and SOC/TP a ios) and he esponse a -
iable (SOC s ocks). The model included SOC s ocks, SOC/TN and SOC/
TP da a om all si es, P le els and dep hs. Following he model es i-
ma ion, we applied a nume ical op imisa ion me hod o iden i y he
SOC/TN and SOC/TP a ios ha would p edic maximised SOC s ocks
wi h 99 % con idence in e als, conside ing all in e ac ions in he da a
se . The op imisa ion p ocess began wi h he o mula ion o an objec i e
unc ion in ended o p edic SOC s ocks based on he polynomial
eg ession model. We chose he “L-BFGS-B” me hod (Zhu e al., 1995)),
which is app op ia e o p oblems ha ha e bounda y cons ain s on he
a iables. To quan i y he unce ain y associa ed wi h hese op imal
a ios, we calcula ed he s anda d e o s using he in e se o he Hessian
ma ix ob ained om he op imisa ion p ocess. All s a is ics we e pe -
o med using R e sion 4.4.1 (R Co e Team, 2021).
Table 2
Soil physico-chemical p ope ies a g assland si es.
Si e P Dep h BD pH SOC TN TP Mehlich3 P Mo gan’s P SOC/TN SOC/TP SOC s ocks
ea men s cm g cm
−3
g kg
−1
mg kg
−1
mg L
-1
C ha
−1
JC1 High 0–10 1.11 (0.08) a 5.24 (0.04) bc 26.94 (0.98) a 2.67 (0.10) a 1.06 (0.06) a 0.88 (0.62) b 11.37 (1.36) a 10.08 (0.01) a 25.53 (1.80) ab 29.86 (3.20) a
10–30 1.32 (0.01) a 5.40 (0.16) ac 10.54 (1.34) b 1.09 (0.12) bc 0.33 (0.07) b 29.78 (4.08) a 1.10 (0.24) bc 9.62 (0.53) a 31.84 (2.72) ab 27.74 (3.80) a
30–50 1.23 (0.17) a 5.78 (0.17) a 5.17 (1.82) c 0.54 (0.26) cd 0.23 (0.09) bc 15.23 (1.36) ab 0.64 (0.47) cd 10.13 (2.05) a 23.22 (6.61) b 12.28 (2.44) b
Low 0–10 1.09 (0.07) a 5.02 (0.05) b 23.79 (2.20) a 2.44 (0.25) ab 0.35 (0.06) b 9.06 (7.84) ab 1.65 (0.35) b 9.77 (0.83) a 68.94 (17.91) a 25.99 (3.99) a
10–30 1.18 (0.29) a 5.38 (0.20) ab 10.87 (1.69) b 1.17 (0.18) ac 0.27 (0.04) bc 10.32 (8.14) ab 0.39 (0.01) cd 9.29 (0.44) a 40.21 (2.42) b 24.96 (3.51) a
30–50 1.56 (0.11) a 5.83 (0.23) a 3.13 (0.39) c 0.34 (0.19) d 0.15 (0.04) c 14.87 (6.95) ab 0.25 (0.12) d 10.90 (4.55) a 20.91 (4.30) c 9.69 (0.64) b
JC2 High 0–10 1.11 (0.03) b 6.16 (0.02) a 22.95 (2.96) ab 2.27 (0.32) ab 0.74 (0.07) a 41.22 (19.75) a 2.84 (1.14) a 10.12 (0.27) a 30.76 (1.10) cd 25.57 (3.88) b
10–30 1.30 (0.12) ab 6.11 (0.08) a 13.02 (1.75) bc 1.38 (0.23) ac 0.47 (0.06) bc 40.54 (12.29) a 0.61 (0.37) b 9.51 (0.59) ab 27.58 (0.59) cd 33.80 (4.29) ab
30–50 1.29 (0.28) ab 6.21 (0.09) a 8.03 (3.97) cd 0.93 (0.47) cd 0.32 (0.13) bd 41.19 (22.78) a 0.27 (0.06) b 8.87 (2.10) ab 24.28 (2.66) d 19.77 (6.92) bc
Low 0–10 1.11 (0.08) b 6.24 (0.23) a 27.45 (6.65) a 2.68 (0.57) b 0.59 (0.07) ac 18.84 (6.76) ab 2.15 (1.04) a 10.19 (0.30) a 46.35 (6.67) a 30.37 (7.64) ab
10–30 1.27 (0.05) ab 6.10 (0.09) a 14.22 (1.85) bc 1.57 (0.16) bc 0.41 (0.06) cd 2.48 (0.17) b 0.50 (0.15) b 9.04 (0.35) ab 34.87 (1.76) ab 36.16 (5.98) a
30–50 1.48 (0.06) a 6.21 (0.10) a 5.05 (0.38) d 0.69 (0.09) d 0.23 (0.01) d 35.91 (20.65) a 0.21 (0.02) b 7.32 (0.49) b 21.52 (1.11) e 14.92 (1.19) bc
LE High 0–10 1.25 7.52 32.40 3.27 0.93 65.02 25.30 9.91 34.84 40.55
10–30 1.42 7.93 11.06 1.25 0.49 7.60 2.00 8.85 22.71 31.51
30–50 1.25 7.95 8.00 0.83 0.41 2.21 0.98 9.63 19.45 20.02
Low 0–10 1.34 7.63 29.74 2.96 0.76 33.47 13.70 10.05 39.10 39.92
10–30 1.41 7.89 9.45 1.09 0.45 2.48 1.05 8.67 20.95 26.70
30–50 1.20 7.96 11.31 1.25 0.49 5.80 1.65 9.04 23.22 27.17
In Table 2, alues ep esen sample means ( o each dep h; n =3 a JC1, JC2; n =1 a LE). Di e en le e s o signi icance acco ding o Tukey’s pos hoc es (p <0.05) ollow s anda d de ia ions in pa en heses. The
compa isons we e made be ween dep hs a high and low P ea men s in each indi idual si es. Same le e s indica e no s a is ical di e ence. P, phospho us; BD, bulk densi y; SOC, soil o ganic ca bon; TN, o al ni ogen;
TP, o al phospho us; SOC/TN and SOC/TP, a ios.
P. Bhople e al.
Geode ma 463 (2025) 117538
4
3. Resul s
3.1. Soil p ope ies
We es ima ed ne phospho us (P) balances (P inpu – P expo in
biomass) ac oss all expe imen al si es o check i we can p o ide a mo e
unc ionally ele an compa ison han nominal “low” e sus “high”
ea men s. Based on si e-speci ic P inpu s, obse ed da a, and li e a u e-
de i ed alues o d y ma e yields and biomass P con en s in s udied
ag oecosys em (G aça e al., 2022; Poeplau e al., 2016; Be gk is e al.,
2011), he esul s o his analysis show ha low P ea men s we e
consis en ly in de ici ac oss g assland and a able sys ems (−11 o −21
kg P ha
−1
y
−1
), indica ing long- e m deple ion o soil P. The high P
ea men s led o su pluses in g asslands ( anging om +6 o +32 kg P
ha
−1
y
−1
) and we e nea ly balanced in a able sys ems ( anging om −4
o +3 kg P ha
−1
y
−1
). This analysis highligh s ha ne P addi ion may
lead o legacy e ilisa ion e ec s and nu ien cons ain s in luencing
SOC s o age pa e ns which can be explo ed mo e in u u e s udies
(Supplemen a y Table 2, Supplemen a y Fig. 1).
Wi h he excep ion o he JC2 g assland and he JY a able si es, he
soil BD did no di e signi ican ly be ween P e ilise ea men s a any
gi en dep h (Tables 2 and 3). In bo h managemen sys ems (g assland
and a able), he BD anged om 1.1 o 1.6 g cm
−3
. The soils we e
gene ally acidic, wi h he pH anging om 5.0 o 6.9 in all g assland and
a able si es, excep o he LE g assland (bo h P ea men s, Table 2) and
he JY a able si e (Table 3), which had neu al o alkaline pH. These
plo s had been limed (12 ha
−1
e e y 7–10 yea s).
The SOC, TN and TP con en s we e signi ican ly highe in opsoil
(0–10 cm) and dec eased wi h dep h a he g assland si es (JC1, JC2,
LE). O e all, he SOC con en s anged om 32.4 g kg
−1
in he opsoil
(0–10 cm) o 3.1 g kg
−1
a a dep h o 30–50 cm ac oss g assland si es
(Table 2). The TN and TP con en s also dec eased signi ican ly wi h
dep h a all g assland si es and anged om 3.3 o 0.3 g kg
−1
TN and 1.0
o 0.2 g kg
−1
TP.
A he a able si es, con en s o SOC and TN we e signi ican ly lowe
in he deepes soil laye (30–50 cm). The SOC con en s anged om 18.1
o 4.4 g kg
−1
and TN con en s om 1.7 o 0.5 g kg
−1
h ough all dep hs
o a able si es (Table 3). The TP con en a ied inconsis en ly h ough
he soil dep hs ac oss he a able si es in he deepes soil laye . A he JY
si e, he TP anged om 0.15 o 0.2 g kg
−1
in 30–50 cm dep h ac oss P
ea men s. A he LS si es only 2 soil eplica es we e a ailable and
ep esen ed a much wide ange (0.85–1.6 g kg
−1
) in TP a 30–50 cm
dep h a LS1 and LS2 si es. A hese si es, he low P ea men s in
pa icula , had much highe TP le els han expec ed in he 30–50 cm soil
laye , which could be due o une en dis ibu ion o P o his laye as a
esul o successi e ull in e sion illage e en s (Table 3).
No consis en end was obse ed in he a ailable P con en s (Meh-
lich3 ex ac ) in he g assland si es JC1 and JC2 o in he a able si es LS1
and LS2, e en wi h di e en P ea men s. Howe e , a ailable P
consis en ly dec eased wi h inc easing soil dep hs a LE and JY si es. In
he g assland si es, he a ailable P con en s anged om 0.9 o 65.0 mg
kg
−1
, while in a able si es hey we e be ween 1.6 and 205.2 mg kg
−1
(Tables 2 and 3). The plan a ailable P (Mo gan’s ex ac ) con en s
consis en ly dec eased om op soil (0–10 cm) o deepe soil dep hs
(10–50 cm) a bo h g assland and a able si es excep o si es JC2 and
LS2. The a ailable P con en s we e gene ally highe in high P ea men s
compa ed o he low P ea men s ac oss all si es (Tables 2 and 3). The
disc epancies be ween Mehlich3 and Mo gan P wi h soil dep h indica e
he dis inc ex ac ion chemis y o hese wo me hods and hei a ge
ac ions a he han di e ences in he disc e e in-si u P pools.
Compa ed o Mo gan’s ex ac an which a ge s a na owe ange o
eadily plan -a ailable P o ms especially unde acidic soil condi ions,
Mehlich3 can mobilise bo h labile and mode a ely bound P o ms due o
highe ex ac ion s eng h. Ou esul s on Mehlich3 P no ollowing he
same dep h ends as Mo gan’s P a e in line wi h he p e ious s udy
which showed di e en ex ac an s esponded a iably du ing e ilise
Table 3
Soil physico-chemical p ope ies a a able si es.
Si e P Dep h BD pH SOC TN TP Mehlich3 P Mo gan’s P SOC/TN SOC/TP SOC s ocks
ea men s cm g cm
−3
g kg
−1
mg kg
−1
mg L
-1
C ha
−1
LS1 High 0–10 1.18 (0.16) a 6.09 (0.10) a 18.07 (0.16) a 1.58 (0.05) a 0.62 (0.01) b 97.09 (4.15) a 2.05 (0.56) a 11.48 (0.46) a 29.27 (0.05) a 21.35 (3.05) c
10–30 1.39 (0.04) a 6.13 (0.11) a 17.11 (1.17) a 1.58 (0.11) a 0.60 (0.03) b 69.12 (29.15) b 1.78 (0.04) ab 10.87 (0.01) a 28.38 (0.48) a 47.49 (1.89) a
30–50 1.12 (0.13) a 6.15 (0.19) a 4.92 (0.06) b 0.57 (0.05) b 0.40 (0.04) c 33.18 (24.62) b 0.48 (0.05) cd 8.63 (0.94) bc 12.33 (1.45) ab 11.04 (1.12) d
Low 0–10 1.26 (0.08) a 6.19 (0.01) a 17.98 (0.28) a 1.66 (0.01) a 0.54 (0.05) ab 37.43 (27.07) b 0.87 (0.04) ce 10.83 (0.26) a 33.22 (2.21) a 22.74 (1.75) b
10–30 1.37 (0.08) a 6.08 (0.01) a 17.59 (1.75) a 1.65 (0.13) a 0.54 (0.00) ab 54.93 (34.86) b 1.00 (0.30) be 10.69 (0.19) ab 32.54 (3.35) a 48.26 (7.50) a
30–50 1.33 (0.04) a 6.29 (0.28) a 5.25 (0.47) b 0.69 (0.01) b 0.86 (0.63) a 31.62 (3.22) b 0.41 (0.03) d 7.66 (0.54) c 8.11 (5.35) b 13.95 (1.65) bd
LS2 High 0–10 1.40 (0.05) a 6.37 (0.17) a 15.35 (0.37) a 1.44 (0.05) a 0.49 (0.01) b 12.84 (4.74) b 1.18 (0.25) ab 10.70 (0.11) ab 31.46 (1.25) a 21.51 (1.21) b
10–30 1.41 (0.05) a 6.31 (0.23) a 15.12 (0.38) a 1.32 (0.00) ab 0.58 (0.05) ab 20.51 (2.72) a 1.50 (0.83) a 11.45 (0.29) a 26.20 (0.65) ab 42.49 (0.51) a
30–50 1.35 (0.01) a 6.66 (0.23) a 4.36 (0.20b 0.57 (0.05) c 0.54 (0.01) ab 1.79 (0.48) c 0.41 (0.03) b 7.72 (1.18) bc 8.02 (0.53) bc 11.79 (0.50) cd
Low 0–10 1.30 (0.02) a 6.42 (0.14) a 15.45 (1.40) a 1.48 (0.05) a 0.55 (0.13) ab 7.58 (2.24) bc 0.68 (0.09) ab 10.43 (0.65) ab 28.57 (4.25) a 19.99 (1.45) ab
10–30 1.34 (0.07) a 6.37 (0.25) a 15.26 (2.10) a 1.45 (0.10) a 0.49 (0.05) b 7.90 (2.46) bc 0.76 (0.15) ab 10.54 (0.78) ab 31.30 (1.90) a 40.70 (3.58) ab
30–50 1.38 (0.07) a 6.77 (0.18) a 4.57 (1.45) b 0.66 (0.30) bc 1.59 (1.45) a 1.56 (0.33) c 0.42 (0.03) b 7.19 (1.00) c 4.11 (2.75) c 12.52 (3.48) c
JY High 0–10 1.28 (0.06) b 7.09 (0.19) a 13.78 (0.45) a 1.02 (0.08) a 0.51 (0.06) a 205.14 (33.93) a 19.30 (3.20) a 13.49 (0.70) a 27.53 (4.24) b 17.56 (0.25) c
10–30 1.44 (0.02) a 7.12 (0.10) a 15.11 (0.19) a 1.08 (0.02) a 0.44 (0.05) a 159.63 (22.36) a 14.23 (0.80) a 13.99 (0.05) a 34.42 (3.88) ab 43.56 (0.42) a
30–50 1.34 (0.06) ab 7.10 (0.11) a 9.73 (0.63) b 0.73 (0.12) b 0.21 (0.02) bc 38.97 (2.85) c 1.03 (0.44) b 13.51 (1.83) a 46.40 (6.89) a 26.19 (2.56) b
Low 0–10 1.36 (0.01) ab 6.88 (0.28) a 14.75 (0.35) a 1.22 (0.03) a 0.30 (0.03) b 78.60 (11.91) b 2.42 (0.45) b 12.09 (0.05) a 49.00 (4.87) a 20.07 (0.32) ab
10–30 1.44 (0.02) a 7.08 (0.12) a 13.61 (0.97) a 1.04 (0.05) a 0.28 (0.05) b 62.33 (11.24) b 1.40 (0.85) b 13.11 (0.69) a 49.01 (5.69) a 39.11 (3.05) a
30–50 1.39 (0.02) ab 6.86 (0.05) a 6.68 (0.47) c 0.50 (0.09) c 0.15 (0.03) c 22.11 (0.28) c 1.13 (0.86) b 13.47 (1.75) a 46.40 (9.87) a 18.61 (1.55) c
In Table 3, alues ep esen sample means ( o each dep h; n =2 a LS1, LS2; n =3 a JY). Di e en le e s o signi icance acco ding o Tukey’s pos hoc es (p <0.05) ollow s anda d de ia ions in pa en heses. The
compa isons we e made be ween dep hs a high and low P ea men s in each indi idual si es. Same le e s indica e no s a is ical di e ence. P, phospho us; BD, bulk densi y; SOC, soil o ganic ca bon; TN, o al ni ogen;
TP, o al phospho us; SOC/TN and SOC/TP, a ios.
P. Bhople e al.
Geode ma 463 (2025) 117538
5
d awdown (Khomenko e al., 2024). The esul s a e also in line wi h he
iew o Ba ow e al. (2021) who emphasised, P ex ac ion me hods
p o ide ope a ional indices o plan -a ailable P and should no be
in e p e a ed as measu ing speci ic, disc e e pools o P in-si u. This
unde sco es he need o ex ac an -speci ic in e p e a ion when e alu-
a ing soil P dynamics ac oss managemen egimes o soil dep hs.
O e all, high a ios o SOC/TN and SOC/TP occu ed a all g assland
si es excep LE and anged be ween 7.3–10.9 o he SOC/TN a io and
19.5–69.0 o he SOC/TP a io ac oss di e en soil dep hs (Table 2).
The same a ios dec eased signi ican ly wi h inc easing dep hs a a able
si es especially a LS1 and LS2 si es, while he o e all ange o SOC/TN
was be ween 7.2 and 14.0 and ha o SOC/TP om 4.1 o 49.0 (Table 3).
3.2. Soil o ganic ca bon s ocks as a ec ed by land use and soil dep h
The P e ilise addi ion had no e ec on SOC s ocks (Fig. 1). In
g assland si es, he SOC s ocks anged om 40.5 C ha
−1
in opsoils o
9.7 C ha
−1
a he 30–50 cm dep h (Fig. 1, Table 2). The SOC s ocks
di e ed signi ican ly be ween he 0–30 cm and 30–50 cm dep hs. In
a able soils, he SOC s ocks anged om 48.3 o 11.0 C ha
−1
(Fig. 1,
Table 3). The highes SOC s ocks in a able si es occu ed a 10–30 cm
dep h, which was signi ican ly g ea e han in 0–10 and 30–50 cm
laye s. In bo h g assland and a able si es, he lowes SOC s ocks we e
ound a 30–50 cm dep h (Fig. 1).
3.3. Rela ionships be ween soil o al N, o al P and SOC s ocks
The soil TN and TP con en s we e gene ally highe in g assland si es
han in a able si es (Fig. 2). The co ela ions be ween hese nu ien s
we e s onge a he g assland si es (R
2
>0.65) compa ed o he a able
si es (R
2
<0.27, Fig. 2). This pa e n was simila o bo h P ea men s
wi hin each land use. As soil TN con en inc eased so did SOC (Fig. 3A).
The s onges and mos signi ican co ela ions be ween SOC s ocks and
TN con en s occu ed a 0–10 cm and 30–50 cm dep h (R
2
>0.79,
Fig. 3A) o he g assland si es. In a able soils he co ela ions be ween
SOC s ocks and TN we e weake compa ed o g asslands si es eaching
up o R
2
>0.57 wi h highe SOC s ocks co ela ing wi h highe TN
con en s a he 10–30 cm soil dep h. While hese ela ionships we e
weakes in deepe soils a 30–50 cm (R
2
<0.18, Fig. 3A). The SOC s ocks
and TP con en s co ela ed signi ican ly (R
2
>0.50, Fig. 3B) a 10–30
and 30–50 cm soil dep hs in bo h land uses while hese ela ionships
we e weak and no signi ican in op 0–10 cm a bo h si es (R
2
<0.12,
Fig. 3B).
3.4. Rela ionships be ween soil a iables and CNP in e ac ions
The i s wo axes o he PCA o dina ion plo (Fig. 4) explained 92.7
% o al a iabili y in he samples (PC1, 68.8 %; PC2, 23.5 %). The
g assland samples we e mo e associa ed wi h SOC, SOC s ocks, TN, a-
ios o SOC/TN, SOC/TP and TN/TP, highligh ing mo e in luence o soil
chemical p ope ies. In con as , a able samples clus e ed along PC2 and
we e associa ed wi h physical soil p ope ies such as BD, sand, sil and
clay and also SOC/TN alues. The PCA biplo also sugges s ha P ac-
ions (Mehlich3 P, Mo gan’s P) and liming u he con ibu e o di e -
en ia ing land use ypes oge he wi h soil dep hs (Fig. 4).
Fo g assland si es, he op imisa ion algo i hm con e ged o an
op imal SOC/TN a io o 10.1 and a SOC/TP a io o 32.6, wi h 95 %
con idence in e als o 8.8–11.4 and 26.0–39.1, espec i ely and p e-
dic ed SOC s ock o 30.9 C ha
−1
(Fig. 5A). Fo he a able si es, he
op imisa ion algo i hm con e ged o an op imal SOC/TN a io o 10.9
and a SOC/TP a io o 29.4 wi h 95 % con idence in e als o 9.7–12.1
and 25.0–33.8, espec i ely, and p edic ed SOC s ock o 33.34 C ha
−1
(Fig. 5B). These alues ep esen he condi ions unde which he p e-
dic ed SOC s ocks a e maximised, gi en he modelled ela ionships.
While he op imisa ion app oach p o ides an in eg a ed iew o SOC/
TN and SOC/TP a ios, he pai wise ela ionships be ween SOC s. SOC/
TP a e also p esen ed in Supplemen a y Table 1. These indica e b oadly
consis en op ima bu wi h weake ela ionships due o he limi ed
numbe o si es and in insic a ia ions.
4. Discussion
4.1. The impac s o land use on SOC s ocks and hei esponse o long-
e m P e ilisa ion ac oss land uses
The esul s in ou s udy do no indica e signi ican e ec s o land uses
on SOC s ocks. Al hough p e ious s udies ha e shown ha g assland
soils can ha e highe SOC s ocks, due o pe ennial deep- oo ing ege-
a ion and educed dis u bance (Kell, 2011; Poeplau e al., 2018), his
was no he case he e. This may be explained by o he si e-speci ic
in e ac ing ac o s, such as clima e, managemen p ac ices, soil ypes,
and nu ien s oichiome y, which oge he can in luence SOC s o age
(Ki kby e al., 2014; Lal, 2018; Poeplau e al., 2018). The SOC s ocks in
he a able si es may e lec compensa o y mechanisms as seen in o he
s udies such as enhanced esidue inpu s unde high P condi ions
Fig. 1. Mean soil o ganic ca bon (SOC) s ocks a di e en P ea men s (high
and low) in g assland and a able si es. Di e en le e s indica e signi ican
di e ence be ween he means (p <0.05) when dep hs we e compa ed ac oss
high and low P ea men s. Same le e s ep esen no s a is ical di e ence be-
ween he means o P ea men s.
P. Bhople e al.
Geode ma 463 (2025) 117538
6
(Poeplau e al., 2018) o he in e ac ions be ween liming and P a ail-
abili y as obse ed a he JY si e (Pede sen e al., 2025).
Ou esul s do no con i m he i s hypo hesis, namely ha highe P
e ilisa ion would lead o highe SOC s ocks. While P addi ion s imu-
la es p ima y p oduc i i y, and hus he quan i y o SOM inpu s o soils
(Spohn and Schleuss, 2019), ou indings sugges ha beyond a ce ain
h eshold addi ional P may no necessa ily ansla e in o measu able
di e ences in SOC s ocks. The lack o signi ican di e ences in SOC
s ocks be ween he high and low P ea men s in bo h g assland and
a able sys ems also align wi h he indings o Poeplau e al. (2016), who
epo ed ha P e ilisa ion unde N-limi ed condi ions can educe SOC
s ocks. Thus, imbalances in nu ien s may nega e he po en ial bene i s
o P addi ions on long- e m SOC s o age. P e ious s udies in g assland
sys ems epo ed mode a e P addi ions enhanced SOC s o age (Poeplau
e al., 2016; Poeplau e al., 2018), bu excessi e P po en ially igge ed
mic obial p iming e ec s leading o SOC loss (G i i hs e al., 2012).
Addi ionally, he wo k o Kelly (2022) highligh s he complexi y o P
e ec s on SOC dynamics and emphasizes he ole o mic obial-media ed
o ganic ma e u no e in g assland soils, which can explain why SOC
emained s able despi e a ying P inpu s in g assland soils. This in-
dica es ha p iming e ec s ep esen sho - e m mic obial esponses
a he han di ec indica o s o cumula i e SOM losses. In Kelly (2022),
o ganic P inpu s induced posi i e p iming and enhanced N mine aliza-
ion, bu hese mic obial shi s did no lead o highe long- e m SOM
decomposi ion. In ac , ela i e o ino ganic P inpu s, o ganic P inpu s
we e associa ed wi h lowe ne SOM losses, unde sco ing ha p iming
esponses migh be sho li ed and ela i ely small in magni ude and
unde speci ic condi ions may exe limi ed e ec s on long- e m SOM
s abili y. Though s onge and mo e equen p iming e ec s could s ill
in luence SOC dynamics. In con as , no expec ed P-induced SOC losses
in a able soils we e obse ed, which migh be due o ini ial low SOC
s ocks limi ing mic obial decomposi ion (Lo enz and Lal, 2005) o
inc eased c op esidue e u ns mi iga ing C losses (Poeplau e al., 2018).
Fu he mo e, inc eases in c op yield we e much g ea e o a able han
g assland si es, so he lack o an impac on SOC s ocks may e lec
inc eased decomposi ion due o inc eased P inpu s a a able si es.
Howe e , i migh also be possible ha SOC inpu s may no be di ec ly
ela ed o P e ilisa ion (e.g., inc eases ha es able yield bu no oo
g ow h o abo eg ound esidue inpu s). Addi ionally, he SOC s ocks
may no be su icien ly esponsi e o be simply de ec able o e he ange
o P inpu s applied in he LTEs, gi en hei in insic a iabili y and long-
e m equilib a ion. O e all, hese indings indica e ha P a ailabili y
alone does no dic a e SOC s ocks bu in e ac s wi h o he bio ic and
abio ic cons ain s, highligh ing he necessi y o balanced e ilisa ion
s a egies ailo ed o speci ic soil and ecosys em con ex o e ec i e
SOC s o age.
4.2. Mul i ace ed ole o P on subsoil C s o age as in luenced by long- e m
P e ilisa ion
We show ha long- e m P e ilisa ion did no signi ican ly inc ease
SOC s ocks in deepe soil laye s (30–50 cm), which leads o he ejec ion
o ou i s hypo hesis. While plan p oduc i i y and o ganic ma e
inpu a e gene ally associa ed wi h inc eased P inpu (Chen e al., 2014),
his did no lead o highe SOC s ocks in deepe laye s o ei he land
uses. Such an absence o signi ican e ec s o P ea men s on SOC s ocks
sugges ha SOC s o age in subsoils migh be egula ed by addi ional
in e ac ing ac o s, such as mic obial cons ain s, soil s uc u e, and
nu ien s oichiome y (Liang e al., 2019). I migh also be because o
he P e ilisa ion did no inc ease P inpu s o he subsoils in any
app eciable manne .
In g asslands, he SOC s ocks we e s able up o 30 cm dep h bu
educed signi ican ly a 30–50 cm, indica ing limi ed subsoil C accu-
mula ion. This is in line wi h p e ious g assland-based s udies demon-
s a ing ha SOC accumula ion in opsoil is d i en by con inuous plan
esidue inpu s along wi h minimal soil dis u bance, while in he deepe
soil laye s, SOC s o age is cons ained by lowe oo densi y and mi-
c obial ac i i y (Lo enz and Lal, 2005; Lynch and Wojciechowski, 2015).
These esul s a e also in line wi h hose o G i i hs e al. (2012), who
epo ed no signi ican SOC changes in g assland soils unde di e en
long- e m P e ilisa ion ea men s and ha he sys em main ained
s able C:N:P a ios. Howe e , in he a able soils, inc eased mic obial
ac i i y and o ganic ma e u no e , as well as illage-induced ae a ion
and soil s uc u al dis up ion could ha e esul ed in lowe SOC s ocks in
he opsoil (0–10 cm) as compa ed o he 10–30 cm soil dep hs. This
appa en di e ence is likely due o he la ge dep h inc emen and
mixing o esidues due o ploughing, which esul ed in SOC concen a-
ion being dis ibu ed o e a g ea e soil olume. Fu he mo e, he mid-
dep h (10–30 cm) showed signi ican ly highe SOC s ocks compa ed o
o he dep hs (0–10 and 30–50 cm), which can be a ibu ed o esidue
inco po a ion ia ploughing. This is in line wi h p e ious obse a ions
sugges ing ha ploughing edis ibu ed o ganic ma e and enhanced
SOC s o age (Fon aine e al., 2007). Likewise, Coonan e al. (2019) also
epo ed esidue inco po a ion and SOC enhancemen a in e media e
dep hs and no signi ican SOC seques a ion in a able subsoils. O e all,
hese indings a e consis en wi h a ecen s udy ha demons a ed ha
he edis ibu ion o C caused by illage plays a mo e impo an ole in
SOC s o age han P e ilisa ion (Peixo o e al., 2021). Addi ionally,
some ecen ials in Ge many and Denma k (Kim e al., 2022; Pede sen
e al., 2025) ha e also shown ha mic obial-media ed decomposi ion
Fig. 2. Rela ionships be ween o al ni ogen (N) and o al phospho us (P) con en s ac oss soil dep hs a di e en P ea men s (high and low) in g assland and
a able si es.
P. Bhople e al.
Geode ma 463 (2025) 117538
7
a es c i ically de e mine subsoil SOC dynamics as opposed o nu ien
addi ions alone. The e o e, despi e known con ibu ions o P e ilisa-
ion owa ds plan p oduc i i y and nu ien cycling, i s di ec in luence
on deepe SOC s ocks emains limi ed and u he illus a es he mul i-
ace ed ole o P o be explo ed ia long- e m expe imen al ials.
4.3. Soil C:N:P s oichiome y and i s ole in SOC s o age ac oss soil
dep hs
The esul s in ou s udy showed nu ien in e ac ions in luenced SOC
dis ibu ion ac oss dep hs, bu P e ec s alone we e no signi ican .
Ins ead, N con en s we e mo e closely ela ed o SOC s ocks, pa icula ly
in g assland sys ems. In g asslands, SOC s ocks in he op soils a ied in
associa ion wi h he a ailabili y o N as indica ed by highe N con en s.
S onge in luences o N a ailabili y and mic obial p ocesses and
decomposi ion dynamics we e p e iously epo ed in g assland sys ems
(Lo enz and Lal, 2005; Liang e al., 2019), suppo ing ou in e ences.
Howe e , in deepe laye s (10–50 cm) highe C/N a ios exhibi signs o
N limi a ion which can cons ain mic obial ac i i y, leading o slowe
decomposi ion and po en ial SOC accumula ion as p e iously seen in a
long- e m P e ilisa ion ial (G i i hs e al., 2012). Fu he mo e,
To es-Sallan e al. (2017) also highligh ed he impo ance o mine al
associa ions in subsoil SOC pe sis ence, which migh pe haps be he case
o obse a ions in SOC dis ibu ion and nu ien in e ac ions in he
Fig. 3A. Rela ionships be ween soil o ganic ca bon (SOC) s ocks and o al ni ogen (N) a di e en P ea men s (high and low) and soil dep h g adien s in g assland
and a able si es.
P. Bhople e al.
Geode ma 463 (2025) 117538
8
g assland sys ems in ou s udy. In con as , a able soils showed di e en
pa e ns o SOC s ock dis ibu ion, whe e signi ican s ocks occu ed a
10–30 cm dep h, po en ially due o soil in e sion and esidue inco po-
a ion. Ou obse a ions o he end in SOC s ocks wi h dep h in a able
soils a e consis en wi h he s udies o Necp´
alo ´
a e al. (2014) and
Fon aine e al. (2007), who showed ha ploughing edis ibu es o ganic
ma e o in e media e dep hs, which p omo es SOC accumula ion bu
does no necessa ily lead o long- e m seques a ion.
The impac s o P a ailabili y on SOC we e ambiguous. P e ious
s udies explo ed OP as a biologically ele an P pool o s udy s oichi-
ome y (Spohn, 2020), pa icula ly due o i s mic obial associa ions.
Howe e , TP emains a widely used indica o in soil biogeochemical
esea ch in he con ex o long- e m s udies (Ki kby e al., 2011), i was
selec ed in ou s udy o ep esen cumula i e P en ichmen in LTE soils.
We in e i o be a ele an me ic o soil s oichiome ic assessmen s
p o iding an in eg a i e measu e o long- e m P s a us in soils. The OP
includes biologically ac i e o ms bu also comp ises s able o ganic
complexes ha may no be eadily plan o mic obes-a ailable (Ba ow
e al., 2021). In con as , TP includes bo h o ganic and mine al-bound
o ms and p o ides a obus p oxy o long- e m P s a us unde legacy
e ilisa ion ha can a ec P a ailabili y and in luence SOC s ocks. The
use o TP has ensu ed analy ical consis ency ac oss si es and enabled
compa isons wi h p e ious LTE-based s oichiome ic s udies (Ki kby
e al., 2011). Howe e , we do acknowledge i s limi a ion o assessing
Fig. 3B. Rela ionships be ween soil o ganic ca bon (SOC) s ocks and o al phospho us (P) a di e en P ea men s (high and low) and soil dep hs in g assland and
a able si es.
P. Bhople e al.
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