Research Collection Doctoral Thesis Phosphorus availability and crop production in seven Swiss field experiments Author(s): Gallet, Anne Publication Date: 2001 Permanent Link: https://doi.org/10.3929/ethz-a-004313259 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection . For more information please consult the Terms of use . ETH Library
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Research Collection
Doctoral Thesis
Phosphorus availability and crop production in seven Swiss fieldexperiments
Phosphorus availability and crop productionin seven Swiss field experiments
A dissertation submitted to the
Swiss Federal Institute of Technology Zurich
For the degree of
Doctor of Natural Sciences
presented by
ANNE GALLET
DEA INPL (France)
born June 19, 1974
citizen of Gradignan (France)
accepted on the recommendation of
Prof. Dr. E. Frossard, examiner
Dr. J.C. Fardeau, co-examiner
Dr. A.N. Sharpley, co-examiner
Dr. S. Sinaj, co-examiner
Zurich, 2001
Table of contents
Table of contents 2
List of abbreviations 5
Summary 9
Résumé 13
General Introduction 17
Phosphorus in soils 18
Role of phosphorus in plants 18
Plant P uptake and requirements 18
Soil P availability 19
P fertilization and residual P 20
Long-term field experiments 21
Environmental issues 22
Thesis objectives 23
Chapter I: Effect of P input / outpout regime on soil P exchangeability,crop yields and P uptake under a temperate climate 25
Abstract 26
Introduction 27
Materials and methods 28
Results and discussion 37
Conclusions 57
Chapter II: Evaluation of four chemical extractions to assess the changesin phosphorus availability induced by three input regimes in seven field
experiments conducted under a temperate climate. 59
Abstract 60
Introduction 61
Table of contents 3
Materials and methods 62
Results and discussion 65
Conclusions 77
Chapter III: Uptake of fresh and residual phosphate fertilizers byLolium perenne and Trifolium repens grown separately or in association 79
Abstract 80
Introduction 81
Materials and methods 83
Results and discussion 95
Conclusions 115
General conclusions 117
Literature cited 125
List of tables and figures 139
Annexes 147
Remerciements 153
Curriculum Vitae 157
List of abbreviations
List of abbreviations 6
List of abbreviations
CP
DAP
DM
EDTA
E,
F,
^lmin-3m
OF
F
L+AL
P
Pi
P-AAEDTA
p-co2
P-H20
Po
P-Olsen
Pt
OP
P
P>exp
concentration of water soluble P (mg P L"1)
diammonium phosphate
dry matter
ethylenediamine tetra-acetic acid
quantity of isotopically exchangeable P at a time t (mg P kg"1 soil)
amount of P isotopically exchangeable within 1 minute
pool of isotopically exchangeable P between lmin and 3 months (mg P kg"1
soil)
pool of P which can not be isotopically exchanged within 3 months (mg P kg"1
soil)
fertilization treatment where no P was applied
fertilization treatment where P was annually applied as triple superphosphate
in quantities equivalent to the offtake by the crops
quantity of available soil P determined according to the Larsen method (mg P
kg"1 soil)
quantity of available P in soil F with residual P (mg P kg"1 soil)
parameter describing the rate of disappearance of the tracer from the solution,
calculated using a linear regression between log r, / R and log(t) for t< 100 min
phosphorus
inorganic phosphorus
quantity of P (mg P kg"1 soil) extracted by ammonium acetate-EDTA
quantity of P (mg P kg"1 soil) extracted by C02-saturated water
quantity of P (mg P kg"1 soil) extracted by deionized water
total organic phosphorus (mg P kg"1 soil)
quantity of P (mg P kg"1 soil) extracted by sodium bicarbonate (NaHC03, pH
8.5)
total phosphorus (mg P kg"1 soil)
fertilization treatment where no P was applied
fertilization treatment where P was applied to cover the crop exportations
fertilization treatment where the quantities of P applied were higher than the
crop exportations
List of abbreviations 7
PDFff%(0F+DAP) fraction of P (%) taken up by the plant derived from the fresh fertilizer on the
OF+DAP treatment
PDFff%(F+DAP) fraction of P (%) taken up by the plant derived from the fresh fertilizer P on
the F+DAP treatment
PDFso1i%(of+dap) fraction of P (%) taken up by the plant derived from the soil on the OF+DAP
treatment
PDFS01i%F fraction of P (%) taken up by the plant derived from the soil on the F treatment
PDFS01|%(i.+DAp) fraction of P (%) taken up by the plant derived from the soil on the F+DAP
treatment
PDFrf%p fraction of P (%) taken up by the plant derived from the residual P on the F
treatment
PDFrf%(F+DAp) fraction of P (%) taken up by the plant derived from the residual P on the
F+DAP treatment
q total P uptake (mg P kg"1 soil)
q0F total P uptake for the OF treatment (mg P kg"1 soil)
q(0F+DAP) total P uptake for the OF+DAP treatment (mg P kg"1 soil)
qF total P uptake for the F treatment (mg P kg"1 soil)
Q(f+dap) total P uptake for the F+DAP treatment (mg P kg"1 soil)
qL P taken up from available soil P (mg P kg'1 soil)
qAL P taken up from available residual P (mg P kg"1 soil)
q'L P taken up from available soil P in the presence of DAP (mg P kg"1 soil)
q'AL P taken up from available residual P in the presence of DAP (mg P kg"1 soil)
qff P taken up by the plant derived from the freshly applied fertilizer (mg P kg"1
soil)
qff(0F+DAP) fresh P fertilizer plant uptake for the OF+DAP treatment (mg P kg"1 soil)
Qff(F+DAP) fresh P fertilizer plant uptake for the F+DAP treatment (mg P kg"1 soil)
qrf P taken up by the plant derived from the residual fertilizer (mg P kg"1 soil)
q,ff residual P plant uptake for the F treatment (mg P kg"1 soil)
qrf(F+DAP) residual P plant uptake for the F+DAP treatment (mg P kg"1 soil)
qSOii P taken up by the plant derived from the soil (mg P kg"1 soil)
List of abbreviations 8
<lsoil(OF+DAP)
IsoilF
<îsoil(F+DAP)
Q
R
R'
R/r,
r0F
r(OF+DAP)
ÎF
r(F+DAP)
rL
rAL
rt
ri
r«,
SA
SADAP
SA0F
SA(0F+DAP)
SAF
SA(F+DAP)
soil plant uptake for the OF+DAP treatment (mg P kg"' soil)
soil plant uptake for the F treatment (mg P kg"1 soil)
soil plant uptake for the F+DAP treatment (mg P kg"1 soil)
total quantity of applied fresh fertilizer (mg P kg"1 soil)
radioactivity (MBq kg"1 soil) used to label the soil available P
radioactivity (MBq kg"1 soil) used to label the total quantity of applied fresh
fertilizer (mg P kg"1 fertilizer)
ratio of total introduced radioactivity R to the radioactivity remaining in
solution after 1 minute of isotopic exchange ^
radioactivity measured in the plant (MBq kg"' soil) grown on the OF treatment
radioactivity measured in the plant (MBq kg"1 soil) grown on the OF+DAP
treatment
radioactivity measured in the plant (MBq kg"1 soil) grown on the F treatment
radioactivity measured in the plant (MBq kg"1 soil) grown on the F +DAP
treatment
radioactivity in the plant coming from the available soil P (MBq kg"1 soil)
radioactivity in the plant coming from the available residual P (MBq kg"1 soil)
radioactivity (MBq) remaining in solution after a time t of isotopic exchange
radioactivity (MBq) remaining in solution after lmin of isotopic exchange
radioactivity (MBq) remaining in solution after an infinite time of isotopic
exchange
specific activity (ratio 33P / 31P)
specific activity ofthe applied fresh fertilizer (MBq mg"1 P)
specific activity in the plant grown on the OF soil (MBq mg"1 P)
specific activity in the plant grown on the OF+DAP treatment (MBq mg"1 P)
specific activity in the plant grown on the F soil (MBq mg"1 P)
specific activity ofthe plant growing on the F+DAP soil (MBq mg"1 P)
Summary
Summary 10
Summary
Phosphorus inputs in agro-ecosystems in amounts exceeding the P needs of plants have
resulted in the accumulation of available P in the surface horizon of most European
soils. Limiting the inputs of phosphate fertilizers in soil presenting a high available P
content can contribute to decrease P losses to ground and surface water. The general
objective of this work was to determine the contribution of residual fertilizations to crop
nutrition, in order to propose new fertilization strategies which would allow a reduction
of agricultural P losses to the environment while maintaining an optimum plant
production.
Seven Swiss long- or middle-term field experiments established on different soil types
and cropped with different rotations (six field crops rotations: Rümlang, FAL,
Eilighausen, Oensingen, Cadenazzo, Changins; one grassland:Vaz) were conducted
during 9 years (for 6 trials) or 27 years (for one trial) testing the effects of 3 P
fertilization regimes (OP: no P, P: P input equivalent to P off-take by crops, P>exp: P
input higher than P off-take) on crop yield, P uptake and soil P availability. The P
balances were calculated as the difference between P input and P off-take by crops. Soil
total, mineral, organic P and soil available P determined by the isotopic exchange
kinetics method and by four extraction methods (P-H2O, P-CO2, P-AAEDTA, P-Olsen)
were measured in the 0-20 cm and 30-50 cm layers of the soils cultivated under field
crop rotations and in the 0-10 cm layer of the grassland soil. Omitting P fertilization
resulted only in one field crop trial in significant yield decreases which were only
observed when the soil available P concentration characterized as the amount of P
isotopically exchangeable within one minute (Eimm) reached values lower than 5 mg P
kg"1 soil. The corresponding values determined by resp. the P-H2O, P-CO2, P-
AAEDTA, P-Olsen, extractions methods were resp. 1.0, 0.5, 34.5, 37.3 mg P kg"1 soil.
Omitting P fertilization decreased significantly P uptake on the grassland trial for soil
available P values much higher than for field crops rotations. Different P sources
contributed to the P nutrition of the crops when no P was applied: soil mineral P
decreased in the upper horizon at almost all sites, soil organic P decreased at two sites
and soil available P decreased in the 30-50 cm horizon. Available P decreased with time
Summary 11
in the upper horizon for all treatments, even when P inputs were higher than the crops
needs, showing that in these soils the higher P inputs were not sufficient to maintain the
high initial available P levels. Final values of isotopic exchange kinetics parameters
(R/ri, n, Cp) and Eimin depended strongly on the initial values (measured at the
beginning of trial) and on the P balance. The decrease of soil P availability measured by
extraction methods was highly correlated to the initial amount and to selected soil
characteristics. Altogether these results suggested that it is possible to model the
decrease in P availability in field crops grown in the absence of P fertilization in similar
agro-climatic conditions.
As soil P testing is of major importance for making sustainable fertilization
recommendations, the four extraction methods mentioned above were evaluated in their
ability to assess soil P availability in the same seven field experiments. This study
showed that each of these extraction methods could give a relevant information on soil
P availability since the amounts extracted were highly significantly correlated to the
amount of P isotopically exchangeable within one minute. A higher correlation
between the amounts of P extracted and the cumulated P balances was observed for the
Olsen extraction, suggesting that this method was the most adapted on the studied
systems to assess the changes in P availability when the soil P status changed. Finally,
the obtained results showed that the actual Swiss interpretation scales of the P-
AAEDTA and P-CO2 methods underestimated the soil available P status.
As residual value of fertilizers could not be estimated in field experiments where yield
is not limited by phosphorus, isotopic techniques were used under controlled conditions
in a pot experiment to estimate the contribution of past and fresh fertilizations to plant
nutrition. English ryegrass (Lolium perenne, cv Bastion) and white clover (Trifolium
repens, cv Milkanova) were grown on soils coming from three of the field experiments
described above: Cadenazzo, Ellighausen and Changins. Treatments with or without
application of fresh DAP (fertilizer-P labelled or not with 33P04) on soils with or
without residual P (residual-P labelled or not with 33P04) allowed the estimation of the
quantities of P taken up by plants coming from different sources of fertilizers. Fourteen
Summary 12
to 62% of the P taken up by the aerial parts of both plants, grown separately or in
association, were derived from the residual P-fertilizers whereas only 7 to 28% were
derived from a fresh P-fertilizer addition. The proportion of P derived from residual P
was mainly controlled by the total amount of P-fertilizers added to the soils, whereas the
proportion of P derived from fresh P-fertilizer was mainly controlled by the
concentration of P in the soil solution. The kinetics of P-uptake derived from the soil,
residual and fresh fertilizers were the same as the kinetics of dry matter yield production
of clover and ryegrass grown separately or in association, suggesting that the uptake of
phosphorus coming from different sources of fertilizers was controlled by the
accumulation of assimilates derived from the photosynthesis.
This work outlined the importance of long-term agricultural research for understanding
the soil-plant-fertilizer interactions and for the implementation of sustainable and
environmentally-sound fertilization strategies.
Résumé
Résumé 14
Résumé
Des apports de phosphore dans les agro-écosystèmes supérieurs aux besoins des
cultures ont conduit à l'accumulation de P disponible dans les horizons de surface de la
plupart des sols européens. Limiter les apports de fertilisants P sur les sols présentant un
niveau élevé en P disponible pourrait contribuer à réduire les pertes de P vers les eaux
de surface et profondes. L'objectif principal de ce travail était donc de déterminer la
contribution des fertilisations résiduelles à la nutrition des cultures afin de mettre en
œuvre de nouvelles stratégies de fertilisation qui permettraient de réduire les pertes de P
d'origine agricole dans l'environnement tout en maintenant un niveau optimal de
production.
Sept expériences suisses de longue ou moyenne durée établies sur différents types de
sols avec différentes rotations (six rotations avec des grandes cultures: Riimlang, FAL,
Ellighausen, Oensingen, Cadenazzo, Changins; une prairie permanente:Vaz) ont été
menées pendant 9 ans (pour 6 essais) ou 27 ans (pour un essai). Ces expériences
testaient les effets de 3 régimes de fertilisation phosphatée (OP: pas de fertilisation, P:
apports de P equivalents aux exportations des cultures, P>exp: apports de P supérieurs
aux exportations) sur les rendements et le prélèvement des cultures, ainsi que sur la
disponibilité du P dans le sol. Les bilans en phosphore ont été calculés en faisant la
différence entre les apports et les exportations des cultures. Le P total, minéral,
organique ainsi que le P disponible mesuré par la méthode des cinétiques d'échange
isotopique et par quatre méthodes d'extraction (P-H20, P-CO2, P-AAEDTA, P-Olsen)
ont été mesurés sur les couches 0-20 cm et 30-50 cm des rotations de grandes cultures et
sur la couche 0-10 cm de la prairie. L'absence de fertilisation a conduit à des
diminutions significatives de rendements des grandes cultures sur un seul essai à partir
de valeurs de P isotopiquement échangeable en une minute (Eimin) inférieures à 5 mg P
kg" soil. Les valeurs correspondantes déterminées par les méthodes P-H2O, P-CO2, P-
AAEDTA, P-Olsen, correspondaient respectivement à 1.0, 0.5, 34.5, 37.3 mg P kg"1
soil. L'absence de fertilisation P a conduit à une diminution significative des
prélèvements sur la prairie, alors que les valeurs de P disponible étaient bien plus
élevées que sur les rotations incluant des grandes cultures. On a montré que différentes
Résumé 15
sources de P ont contribué à la nutrition des cultures, car le P minéral a diminué dans
l'horizon supérieur de presque tous les sites, le P organique a diminué dans deux sites,
et le P disponible a décru dans l'horizon 30-50 cm. Le P disponible dans l'horizon
supérieur a diminué dans le temps pour tous les traitements même quand les apports
étaient supérieurs aux exportations des cultures. Ceci montre que dans ces sols, ces
apports élevés n'étaient pas suffisants pour maintenir des niveaux initiaux en P
disponible élevés. On a montré que les valeurs finales des paramètres des cinétiques
d'échange isotopique ((R/ri, n, Cp) et Eimin dépendaient fortement des valeurs initiales
(mesurées au début des essais) et du bilan. De même, la décroissance de la disponibilité
mesurée par les méthodes d'extraction était fortement corrélée aux quantités de départ
extraites et à certaines caractéristiques du sol. Tous ces résultats suggèrent qu'il est
possible de modéliser en absence de fertilisation P la décroissance de la disponibilité de
cet élément sur les rotations de grandes cultures dans des conditions agro-climatiques de
même nature.
Comme l'évaluation du statut phosphaté du sol est extrêmement importante pour établir
des recommendations de fertilisation durables, les quatre méthodes d'extraction
mentionnées plus haut ont été évaluées pour leur capacité à évaluer le P disponible dans
les sept mêmes expériences de longue durée. Chacune des méthodes était capable de
fournir des informations satisfaisantes sur la disponibilité du P, puisque les quantités
extraites étaient toutes hautement corrélées au P isotopiquement échangeable en une
minute. Une corrélation plus élevée a été cependant observée entre les quantités
extraites par la méthode Olsen et les bilans cumulés, ce qui montre que pour les
systèmes étudiés, cette méthode pourrait être la mieux adaptée pour estimer les
changements de disponibilité de P quand le statut P du sol change. Enfin, les résultats
obtenus ont montré que les barèmes actuels d'interprétation des méthodes P-CO2 et P-
AAEDTA sous-estiment le statut des sols en P disponible.
Comme il n'est pas possible d'estimer la valeur résiduelle des fertilisants sur des essais
où le P n'est pas un facteur limitant de la production, la contribution de fertilisations
fraîche et résiduelles a été mesurée dans une expérience en pots, en conditions
Résumé 16
contrôlées, à l'aide de techniques isotopiques. On a fait pousser du raygras anglais
(Lolium perenne, cv Bastion) et du trèfle blanc (Trifolium repens, cv Milkanova) sur
des sols provenant de trois des expériences de longue durée décrites plus haut:
Cadenazzo, Ellighausen et Changins. Grâce à des traitements où une fertilisation P
fraîche sous forme de DAP (fertilisant marqué ou non avec du PO4) était appliquée ou
non sur des sols avec ou sans P résiduel (P résiduel marqué ou non avec du PO4), on a
pu estimer les quantités de P prélevées par les plantes provenant des différentes sources
de fertilisation. De 14 à 62% du P prélevé par les parties aériennes des deux plantes
seules ou en association provenaient des fertilisations résiduelles alors que seulement de
7 à 28% avaient pour origine l'addition récente de P. La proportion de P dérivée des
fertilisations résiduelles était contrôlée essentiellement par la quantité totale de
fertilisants appliquée dans les sols, alors que la proportion de P dérivée de la fertilisation
récente était plutôt dépendante de la concentration en P dans la solution du sol. Les
cinétiques de prélèvement de P provenant du sol, des fertilisations résiduelles et fraîche
étaient les mêmes que celles de la production de matière sèche. Ceci suggère que le
prélèvement de P provenant de différentes sources de fertilisants était contrôlé par
l'accumulation dans la plante des assimilats dérivant de la photosynthèse.
Ce travail souligne l'importance de la recherche de longue durée en agriculture afin de
comprendre les interactions sol-plante-fertilisant, et de mettre en œuvre des stratégies de
fertilisation durables et respectueuses de l'environnement.
General introduction
General introduction 18
Phosphorus in soils
Soils contain between 100 and 3000 mg P kg-1 soil (Frossard et al, 2000). In
uncultivated soils, the soil parent material and the pedogenesis determine the nature and
stability of native P (Walker and Syers, 1976) while P inputs are generally small.
Agricultural systems are characterised by increased P inputs through fertilization and by
increased P outputs through crops removals. Finally, the low concentration and low
solubility of phosphorus in soils make it commonly a growth limiting nutrient in soils.
Role ofphosphorus in plants
Phosphorus is an essential constituant of nucleic acids composing DNA and RNA
molecules, and therefore plays a key-role in the constitution and translation of genetic
information. Phospholipids are constituants of biomembranes, P as ATP has a central
role in the energy transfer in the cell (Marschner, 1995). During the vegetative stage of
growth, phosphorus requirement for optimal growth is in the range of 0.3-0.5% dry
matter. P deficiency results in reduced leaf growth, reduced photosynthesic activity and
therefore reduced root growth and crop yield (Plénet et al., 2000; Mollier and Pellerin,
1999).
Plant P uptake and requirements
Plants act as a sink for P. Phosphorus is taken up by roots from the soil solution mainly
as orthophosphate ions H2PO4" and HPO42". This is an active, energy dependent process
where uptake occurs against an electrochemical gradient and is mediated by a H
cotransport (review by Frossard et al., 1995). Plants have access to soil P by three
mecanisms: root interception (negligible), mass flow and diffusion, which is the
movement of a substance from one region to adjacent regions where that species has a
lower concentration. Ninety five percent of P taken up by crop plants is attributed to
diffusion from the soil to the root (Jungk and Claassen, 1997). Diffusion depends on
soil characteristics, water content, structure, etc and plant characteristics, such as
kinetics of P uptake, size and morphological properties of the root systems, the
symbiosis with mycorrhizae. Moreover, the exudation of protons, of low molecular
weight organic ligands or enzymes in the rhizosphere may contribute to the liberation of
General introduction 19
Pi from insoluble Pi forms or from organic P (Frossard et al., 1995). Plant species differ
in their internal requirements, i.e. the amount of P needed in the plant to produce one
unit of dry matter (P concentration) and in their external P requirements, i.e. the needed
P content in soil to achieve a satisfying yield (Föhse et al., 1988). Responsiveness to P
fertilization therefore vary among plant species (Greenwood et al., 1980). For instance,
yield variations depend much more on variations of soil P level for beet or potato than
for wheat or maize. For the particular case of the Swiss agriculture, field crops
exportations are ranging between 20 kg P ha"1 year"1 for barley and 49 kg P ha"1 year"1
for beet, and between 9 and 47 kg P ha"1 year"1 for grassland, depending on the use
intensity (Walter at al., 2001).
Soil P availability
In Western European soils, the P from the soil solution represents in average only 2% of
the total plant uptake (Fardeau, 1996). Consequently, during plant growth, most of the
plant Pi has to be delivered from the solid phase of the soil by a combination of abiotic
processes such as dissolution and desorption, and biotic processes such as
mineralisation (Frossard et al., 2000).
Pi availability is characterised by three factors (Beckett and White, 1964): (i) the
intensity factor, which is the activity of phosphate ions in the soil solution, (ii) the
quantity factor, which is the amount of P that can be released from the soil solid phase
into the soil solution, and (iii) the buffer capacity, which describes the ability of a soil to
maintain the intensity constant when the quantity varies.
P fertilization of agricultural soils is generally needed to maintain the initial soil P
fertility or to increase it if it is low, in order to reach a satisfying level of crop
production. Phosphorus availability has therefore to be estimated in order to make
appropriate fertilizer recommendations. Different methods can be used for this purpose:
the isotopic exchange (Fardeau, 1996) that will be fully described in the first chapter of
this thesis, other methods using an anion exchange resin (Sibbesen, 1978), or an infinite
sink (Lookman et al. 1995) and extraction methods (Kamprath and Watson, 1980).
Chemical extractions with water, acids or bases remain the most simple, rapid and
cheap methods to estimate soil P availability, even if it has been shown that they extract
General introduction 20
variable proportions of available and unavailable P (Fardeau et al, 1988; Kato et al,
1995). The amounts of P extracted are generally correlated to the crops yield and uptake
in order to determine a so-called "critical P level", which is an estimate of the optimum
P status for an optimum crop production (Dahnke and Olson, 1990). Once this critical
value has been determined, soil P supply can be divided into different categories (for
instance low, medium, high) corresponding to the different probabilities to obtain a crop
response to applied nutrient. This evaluation of soil P status as respectively high,
medium or low will afterwards determine the P fertilizer quantities to be applied: e.g. no
P, P applications covering crop offtakes, P applications higher than crop offtakes
(Tunney et al. 1997). In Switzerland, two extraction methods are used: C02-saturated
water (Dirks-Scheffer, 1930) and ammonium acetate EDTA (Cottenie et al., 1982).
More details will be given on these methods in the Chapter 2 of this thesis.
Pfertilization and residual P
P fertilizers can be added as water soluble inorganic fertilizers, as less soluble inorganic
fertilizers (rock phosphates) and as organic fertilizers of varying origins. In this thesis
only fertilization with water soluble inorganic fertilizers will be studied. When a P
fertilizer is added to soil, complex reactions occur (Sample et al., 1980): phosphate is
closely and chemically bonded to the surface of Fe and Al oxides, or with CaC03 in
calcareous soils. These reactions take place in two steps: a rapid step in which some of
the phosphate ions are adsorbed on the surface of soil particles, then a slower step in
which phosphate is converted in a more firmly held form with solid-state diffusion
processes (Barrow, 1980). The fraction of P applied transferred on soil components
varies with soils, but it increases when time of contact between soil and phosphate and
temperature increase for all soils (Barrow, 1983). When fresh soluble fertilizers are
applied to agricultural soils, only a small proportion (from nearly 0% to 15%) of such
fertilizers is taken up by crops the first year (Morel, 1988; Morel and Fardeau, 1990)
and gradually less the following years. Consequently, up to 85 % of the P applied one
year remains in the soil and react with soil components or becomes for a limited fraction
microbial P (Fardeau, 1996). Nevertheless, the residual P can contribute to the nutrition
of present crops. This residual value of past fertilizations has been measured most of the
General introduction 21
times in P limited soils, where differences of crops yield or uptake could be observed in
presence of residual fertilizers (Barrow, 1980; Mendoza, 1992; Bolland et al., 1999). On
soils where plant nutrition is not limited by phosphorus, residual value of fertilizers can
be measured with isotopic techniques (Morel, 1988; Morel and Fardeau, 1989 a and b).
These techniques will be presented in detail in the third chapter of this thesis. Residual
value of fertilizer can be also measured in long-term field experiments by comparing
yield and crop uptake obtained on fertilized plots with those obtained on plots where
fertilization was omitted (Boniface and Trocmé, 1988; Mc Collum, 1991).
Long-termfield experiments
Long-term field experiments are indispensable for agricultural and ecological research
(Poulton, 1996). They allow to identify the biological, and physico-chemical factors
which control the productivity of agricultural systems. The long-term field studies are
essential because many soil properties change very slowly over time, and it is therefore
difficult to detect the effects of a particular treatment on short-term experiments. In the
particular case of phosphorus, it is difficult to detect many effects quickly, because of
the high reactivity and buffering capacity of P in soils and the interactions with soil
inorganic and organic components that happen simultaneously (Rubask, 1999). Long-
term field experiments allow to determine the critical soil P levels below which yield of
crops will decline appreciably. They are an essential tool for the calibration of
extraction methods, as seen before. Moreover, observations in agricultural research may
have a great variability due to soil properties, climate, varieties, etc and long-term
observations are also required to separate a trend from a very variable background
(Southwood, 1994). Finally calculations of P balances (P inputs minus P outputs) can
only be made over long periods, because it is difficult to measure accurately small
changes over short periods against the large quantities of P usually present in soil.
Long-term field experiments provide not only informations on nutrient cycling in
agrosystems, but they are also the basis for long-term political objectives, such as for
example the introduction of legislation which limits the inputs to the land (Ellmer et al.,
2000). Long-term research is therefore essential for the establishment of a sustainable
agriculture, and particularly the sustainable management of the limited resources in P
General introduction 22
implies to consider the long-term effects of different P fertilization strategies not only
on the crops but also on the environment.
Environmental issues
Phosphorus applied as fertilizer to arable lands often improves crop production. The
extent of P fertilization varies greatly between developed and industrialised countries. In
general, P deficiency is typical of developing countries (Sanchez and Uehara, 1980),
whereas high application rates in the industrialised ones have raised environmental
issues (Sharpley and Menzel, 1987). Long-term application of phosphate fertilizers at
levels exceeding crop requirements have resulted in the accumulation of high
concentration of available P in the surface horizon of most European soils (Sibbesen
and Runge-Metzger, 1995). This has increased the losses through runoff, erosion and
leaching of P from agroecosystems to ground and surface waters (Sharpley and Withers,
1994; Sinaj et al., 2002). In Switzerland, in 1995, the total P inputs in agriculture was
20000 t year"1 (51% mineral fertilizers) and the P balance calculated between 1975 and
1995 was a positive balance of+13kg P ha"1 (Spiess and Besson, 1999). Furthermore,
the eutrophication of some lakes on the Swiss plateau was related to diffuse P losses
from agricultural soils which had been heavily fertilized with organic and inorganic
sources of P (Stamm et al., 1998; Gächter et al, 1996). In order to limit the losses of P
to the environment, the Swiss agricultural authorities have proposed, within the frame
work of "integrated production" to calculate the P fertilization according the following
criteria (Walter et al., 1994): (i) the P requirements of the crops, defined by the quantity
of P contained in harvested products, (ii) the P level in the surface horizon, which is
determined using a chemical extraction to measure a quantity, corrected using the soil's
clay content as an indicator of the soil's buffer capacity, (iii) the P balance of the
complete farm, which has to be equilibrated. However, in order to limit these
environmental problems linked to P losses, it is maybe not only necessary to limit P
inputs but also, if crop yields and quality remain unaffected, to even decrease soil P
availability.
General introduction 23
Thesis objectives
As most of the Western European soils, Swiss agricultural soils have been fertilized for
many years, in amounts larger than the crops exportations, and this excess of P
fertilizers should have accumulated in soils. The main hypothesis of this work was that
fertilizers added in the past could contribute to the nutrition of present crops and that it
was possible to stop P fertilization during a time to be defined without any negative
effect on crop production. The objective of this thesis was therefore to determine the
contribution of residual fertilizations to crop nutrition, in order to implement new
fertilization strategies which would allow a reduction of agricultural P losses to
environment while maintaining an optimum plant production.
In the first chapter, we have studied the influence of three different P fertilization
regimes (OP, no P applied since the beginning of the trials; P: P fertilization covering
the crop exportations; P>exp: P fertilization higher than the crops exportations) on crop
yield and P uptake in seven Swiss long- or middle-term field experiments with different
rotations of crops with different P requirements. In this part, soil P availability was
determined with the isotopic exchange kinetics method of Fardeau (1996).
As extraction methods remain the routine methods to estimate soil P availability and
therefore to make fertilizer recommendations, we have evaluated in the second chapter
four extractions methods in their capability to assess the changes in phosphorus
availability induced by the same P fertilization treatments in the same field experiments
as in the chapter 1. The extraction methods tested were water extraction, sodium
bicarbonate extraction (Olsen et al., 1954), and two methods commonly used in
Switzerland: C02-saturated water (Dirks-Scheffer, 1930) and ammonium acetate EDTA
extraction (Cottenie et al., 1982). Extraction results were compared to those obtained
with the isotopic exchange method (Fardeau, 1996), used as a reference for P
availability determination.
In the third chapter, we assessed in a pot experiment by the use of isotopic techniques
(Morel and Fardeau, 1989 a and b) the efficiency of fertilizers applied either in the past
General introduction 24
or freshly for two plants grown separatly and in association, Lolium perenne and
Trifolium repens, and on soils non limited in P coming of three of the seven field
experiments cited above.
CHAPTER I
Effect of P input / output regime on soil P exchangeability, crop yields and P
uptake under a temperate climate
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 26
Abstract
Limiting the inputs of phosphate (P) fertilizers in soil of high available P concentration
can contribute to decrease P losses to ground and surface water. However, such a
strategy is acceptable only if crop yields remain unaffected. Seven Swiss field
experiments established on a wide range of soil types and cropped with different
rotations (6 field crops rotations, 1 grassland) were conducted during 9 years (for 6
trials) or 27 years (for one trial) evaluating the effects of 3 P fertilization regimes (no P,
P input equivalent to P off-take by crops, P input higher than P off-take) on crop yield,
P uptake and soil P availability. The P balances were calculated as the difference
between P input and P off-take by crops. Soil total, inorganic, organic P and available
soil P determined by isotopic exchange kinetics were measured in 0-20 cm and 30-50
cm layers of soils cultivated under field crop rotations and in the 0-10 cm layer of the
grassland soil. Omitting P fertilization resulted only in one field crop trial in significant
yield decreases, which were only observed when the available soil P concentration (i.e.
the amount of P isotopically exchangeable within one minute (Eimin) reached values
lower than 5 mg P kg"1 soil. Omitting P fertilization significantly decreased P uptake on
the grassland trial. When no P was applied, soil inorganic P decreased in the upper
horizon at almost all sites (from 468 to 418 mg P kg"1 soil in average), soil organic P
decreased at two sites (from 515 to 466 mg P kg"1 soil in average), suggesting that
different P sources contributed to the P nutrition of the crops. Available P decreased
with time in the upper horizon for all treatments (from 15.6 to 7.4 mg P kg"1 soil in
average), even when P inputs were higher than the crops needed, showing that in these
soils, the higher P inputs were not sufficient to maintain the high initial available P
levels. Final values of isotopic exchange kinetics parameters (R/ri, n, Cp) and Eimin
depended strongly on initial values (measured at the beginning of trial) and on P
balance. These results suggest that knowing initial soil P availability and expected P
balance, it is possible to predict the decrease of available soil P in field crops grown in
the absence of P fertilization in similar agro-climatic conditions as those studied here.
Key-words: field crop rotations, field experiments, isotopic exchange kinetics, grassland, P availability,
phosphorus fertilization
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 27
Introduction
Phosphorus inputs in agro-ecosystems in amounts exceeding the P needs of plants
resulted in the accumulation of high concentration of available P in the surface horizon
of most European soils (Sibbesen and Runge-Metzger, 1995). The transfer of P from
agricultural soils to water bodies is positively correlated to the soil available P content
(Sibbesen and Sharpley, 1997). To limit the environmental problems linked to P losses
it is therefore necessary to limit P inputs and in certain cases to decrease soil P
availability. However this can only be accepted if crop yields remain unaffected by the
decreased rates P of fertilization.
The effect of different rates of P fertilization on crop yield and soil P availability can
only be answered by long-term field experiments. Works published for the Temperate
Zone determining critical levels of available P under which the yields of specific crops
significantly decreased, have been carried in a limited number of situations (Mc Collum,
1991; Webb et al., 1992; Stumpe et al., 1994; Jungk et al., 1993; Rubaek, 2000; Morel et
al., 1992). These works showed that depending on the initial soil P status, on the
climatic conditions and crop P requirements, the time during which P fertilization can
be omitted without any significant yield losses or differences in P uptake varies from 1
(Richards et al., 1998) to 60 years (Ellmer et al., 2000). However in most of the cases
the omission of P fertilization for periods shorter than 10 years had no significant effect
on crop yield (Boniface and Trocmé, 1988; Jaakola et al., 1997; Gransee and Merbach,
2000). This set of data must, however, be completed to identify the soil available P level
above which the yield of different crops grown under different environmental
conditions does not increase after an additional P fertilization, and the soil available P
level below which P fertilization systematically increases yields. Furthermore
information is needed to predict how long can P fertilization be omitted without
affecting yield in rotation including crops with high P requirements grown under
different environmental conditions.
The objective of the present work was to study the influence of different P fertilization
regimes (no P application, P inputs covering crop exportations, P inputs higher than
crop needs) on crop yield and P uptake in seven field experiments in which crops with
different P requirements were grown in different rotations. These parameters were then
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 28
compared to the changes in total, inorganic, organic, and soil available P measured after
4 and 9 years for six of the seven field experiments and after 22 and 27 years for the last
trial. Soil P availability was assessed using an isotopic method (Fardeau, 1996).
Materials and Methods
Experimental sites andPfertilization treatments
Six of the seven field experiments were established by the Swiss Federal Station for
Agroecology (Zurich) in 1989 in Rümlang (canton of Zurich), Reckenholz-FAL (canton
of Zurich), Ellighausen (canton of Thurgau), Oensingen (canton of Aargau), Cadenazzo
(canton of Ticino) and Vaz (canton of Graubünden). The oldest trial was established in
1971 by the Swiss Federal Research Station for Plant Production (Nyon) in Changins
(canton of Geneva). All trials are still ongoing. Their location, climate and soil
characteristics are given in Tables 1.1 and 1.2. Rotations were field crops at all sites
excepted at Vaz that was under permanent grassland (Table 1.3).
The experiments had one factor randomized block design with six different phosphorus
rates at Rümlang, FAL, Ellighausen, Oensingen and Cadenazzo. There were 4 field
replicates for each P level. Each microplot had a length of 8.25 m and a width of 4 m
(except Cadenazzo: length of 8 m and width of 4.5 m), and a distance of 1.25 m
separated micro-plots along the smallest side. P treatments studied were OP: no P
applied; P: P applied as triple superphosphate in quantities equivalent to the P off-take
by the crops; P>exp: P applied as triple superphosphate in quantities higher than the
off-take by the crops (5/3 of the P off-take). Apart from P, all the other nutrients were
applied in the trial according to the Swiss guidelines for integrated production (Walter
et al., 1994), i.e. the nutrients were applied according to the requirements of the crops
and their availability in the soil. The micro-plots were ploughed along their longest side
and crop residues were taken off the field.
At Changins, the experiment had a randomized block design with 5 different treatments
P-K and 4 field replicates. Each micro-plot had a length of 15 m and a width of 8m, and
a distance of 1 m separated micro-plots along the smallest side. Treatments studied were
I.EffectofPinput/output
regi
meon
soilPexchangeability,
cropyi
elds
andPuptake
29
Table
1.1.Main
characteristicsofthesevenex
peri
ment
alsites.
Experimental
FAO
location
altitude
meanannual
prec
ipit
ation
plough
soil
apparentdensityof
site
soil
classification
temperature
depth
surfacehorizon
(m)
(°C)
(mm)
(cm)
(g.c
m"3)
Rümlang
CalcaricCambisol
681.95E/254.82N
443
8.5
1042
25
1.37
FAL
EutricGl
eyso
l681.95E/254.82N
443
8.5
1042
25
1.14
Elli
ghau
sen
EutricCambisol
728.1IE/274.62N
440
8.5
916
25
1.22
Oensingen
Gley
i-ca
lcar
icCambisol
622.10E/237.07N
422
8.2
1013
25
1.3
Cadenazzo
EutricFluvisol
715.50E/113.21N
197
10.5
1772
25
1.22
Changins
Gley
icCambisol
507.85W/139.30N
438
9.5
940
25
1.22
Vaz
Gley
icFluvisol
759.01E/173.08N
1190
4.9
1042
10
1.07
Table
1.2.Mainph
ysic
o-ch
emic
alcharacteristicsofthesurfacehorizonofthestudied
soils.
Experimental
site
pH(H20)
Corg
clay
sand
Aid
Fed
CEC
cmol
ckg
"1&KB
Rümlang
7.9
20
240
458
1.22
11.22
21.3
FAL
7.4
27
388
260
1.42
11.94
35.1
Ellighau
sen
6.7
23
329
307
1.74
9.10
37.0
Oensingen
7.0
24
370
225
1.29
14.82
26.6
Cadenazzo
6.3
14
91
362
1.09
8.35
14.3
Changins
6.7
48
540
160
1.93
15.88
29.4
Vaz
6.8
65
273
397
n.d.
n.d.
n.d
I.EffectofPin
put/
outp
utre
gime
on
soilP
exchangeability,
cropyi
elds
andPuptake
30
Table
1.3.
Croprotationsforthedifferentex
peri
ment
alstations.
19711989
1990
1991
1992
1993
1994
1995
1996
1997
1998
Rümlang
*grass.R
wheat
maize
wheat
/grass.R
potato
wheat
/grass.R
grass.R
potato
wheat
FAL
grass.R
wheat
maize
wheat
potato
wheat
/grass.R
grass.R
potato
wheat
Ellighausen
wheat
potato
barl
ey/grass.R
maize
beet
grass.R
grass.R
potato
wheat
Oensingen
barl
ey/grass.R
maize
wheat
/grass.R
beet
grass.R
grass.R
maize
beet
wheat
/grass.R
Cadenazzo
maize
soybean
potato
wheat
/grass.R
grass.R
maize
/grass.R
soybean
potato
wheat
Changins
*w/m/w/r
rape
wheat
maize
wheat
rape
wheat
maize
wheat
rape
Vaz
*Per.grass.
Per.grass.
Per.grass.
Per.grass.
Per.grass.
Per.grass.
Per.grass.
Per.grass.
Per.grass.
Abbreviations
*w/m/w/r:rotationwheat-maize-wheat-rape
*grass.R:grasslandincludedincroprotation
*Per.grass:permanentgrassland
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 31
OP: no P,no K applied; P: P as triple superphosphate and K applied in quantities
equivalent to the off-take by the crops and P>exp: P applied as triple superphosphate in
quantities equivalent to the off-take by the crops with an additional fertilization of 26.2
kg P ha"1, and 166 kg K ha"1 were added to the normal K fertilization. N was applied in
the trial according to the Swiss guidelines for integrated production (Walter et al.,
1994). The micro-plots were ploughed along their longest side and crop residues were
left on the field.
In Vaz the trial was a 4x4 factorial experiment including four different rates for
phosphorus and potassium. Each micro-plot had a length of 5 m and a width of 2 m, and
a distance of 1 m between micro-plots along the smallest side. Three P treatments were
studied in this trial: OP no P applied; P: P spread at the surface as triple superphosphate
in quantities equivalent to the off-take by the crops and P>exp: P applied as triple
superphosphate in quantities higher than the off-take by the crop (3/2 of the P off-take).
Potassium was applied at the same rate: 179.3kg K ha"1, while N was applied according
to the Swiss guidelines for integrated production (Walter et al., 1994).
Soil sampling
Soils were sampled yearly, after the harvest and before the fertilizer application, from
the plough (0-20 cm) and the 30-50 cm layers for all sites except Changins (only the 0-
20 cm layer) and Vaz (grassland) where the soil was only sampled from the topsoil, 0-
10 cm layer. At least 8 cores with a diameter of 2.5-3 cm were taken randomly within
the fertilized area of each plot. Plant residues were removed from the soil and the
individual samples were mixed to form a composite sample per plot. The soils were
then air-dried and sieved at 2 mm before being used for further analysis. To compare
treatment effects with the original soil status, samples of the plough layer from 1989
(the first year of the trial), 1993 and 1998 were analyzed for all sites except Changins
where, because of the lack of the initial samples, only the samples from 1993 and 1998
were analyzed. Samples from the 30-50 cm layer were analyzed in 1989 and 1998.
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 32
Phosphorus analyses
Total, inorganic and organic phosphorus. Total phosphorus (Pt) and total inorganic
phosphorus (Pi) were measured using the ignition method described by Saunders and
Williams (1955). One gram of soil sample was ignited at 550 °C for 1 hour. Both
ignited and unignited soil samples (1 g) were then extracted with 50 ml 0.5 M H2SO4
for 16 hours. The P in the extracts was determined using malachite green colorimetry
(Ohno and Zibilski, 1991) after filtration of the extracts (Whatman 40). The quantity of
P extracted from the ignited soil was considered as the total P content of the soil. The
quantity of P extracted from the non-ignited soil was considered as the total inorganic P
content of the soil. The total organic P (Po) was calculated as the difference between
total P and total inorganic P. For these agricultural soils, P extracted with H2SO4 from
ignited soils was not different (p<0.001, data not shown) from the total P extracted from
0.5 g dry soil with a microwave digestion method (Microdigest A 301, Prolabo)
combining subsequently an extraction with 5 ml concentrated (95-97%) H2SO4 during
15 min at a 70 W microwave power, with H2O2 30% (8 ml added in 4 steps of 2 min
with a 80 W microwave power) and with concentrated (70%) HCIO4 (5 ml added in 2
steps of 10 min with a 40 W microwave power)
Isotopic exchange kinetics. According to Beckett and White (1964), P availability is
governed by three factors: (i) the intensityfactor, which is the activity of phosphate ions
(H2PÛ4~; HPO4 ~) in the soil solution; (ii) the quantity factor, which is the amount of
phosphate ions that can be released into the soil solution from the solid phase of the soil
during the interval of time considered for plant growth and (iii) the buffer capacity,
which describes the ability of a soil to maintain the intensity factor constant when the
quantity varies.
The experimental procedure of the isotopic exchange kinetics method, conducted on a
soil-solution system in a steady-state with a soil solution ratio of 1:10 has been recently
described (Fardeau, 1996; Frossard and Sinaj, 1997). After an addition of a solution of
carrier-free PO4 ions to a soil solution system in steady-state, the soil solution is
sampled four times from 1 to 100 minutes. When 33PÛ4 ions are added to a soil solution
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 33
system at a steady-state equilibrium, the radioactivity in solution decreases with time
according to the following equation (Fardeau et al, 1985):
rt/R = (n/R) x [t + (n/R)1/n ]-n + rJR [1]
where R is the total introduced radioactivity (= 0.1 MBq); n and rx are, respectively, the
radioactivity (MBq) remaining in the solution between 1 minute and infinity, and n is a
parameter describing the rate of disappearance of the radioactive tracer from the
solution after 1 minute. The parameter n is calculated as the slope of the linear
regression between log [r(t/R] and log(t). The ratio r«, /R, which is the maximum
possible dilution of the isotope, is operationally approximated by the ratio of the water
soluble P to the total inorganic P of the soil (Pl5 expressed in mg P kg"1 soil; Fardeau,
1996). Thus:
roo/R=10xCp/P1 [2]
where Cp is the water soluble P (mg P L"1). The factor 10 arises from the fact that,
during the experiment of isotopic exchange, the soil: solution ratio is 1:10 so that 10 x
Cp is equivalent to the water-soluble P quantity in the soil expressed in mg kg" .
The quantity, E(t) (mg P kg"1 soil), of isotopically exchangeable P at a time t can be
calculated assuming that (i) 31P04 and 33PÛ4 ions have the same fate in the system and
(ii) whatever the time, t, the specific activity of the phosphate ions in the soil solution is
similar to that of the isotopically exchanged phosphate ions in the whole system:
rt/(10xCp) = R/E(t) [3]
Therefore, Et = 10 x CP x (R/rt) [4]
For t = 1 minute, Eimi„ = 10 x CP x (R/ri) [5]
R/n is an estimation of the P-ions buffering capacity of soils (Frossard et al., 1993;
Salcedo et al., 1991; Sen Tran et al., 1988). With R/n being higher than 5, the buffering
capacity is considered to be high, with 2.5 - 5 medium and below 2.5 low.
To obtain data that are relevant from an agronomic point of view, Fardeau (1996)
proposed the following pools depicting P availability.
I. Effect ofP input/output regime on soil P exchangeability, crop yields and P uptake 34
(i) The pool of P exchangeable within 1 minute (Eimin). Ions present in this pool are
composed of ions in the soil solution and those ions that are adsorbed on the solid phase
of the soil but have the same kinetic properties than those in solution (Fardeau et al.,
1985; Morel et al., 2000). Phosphate ions located in this compartment are completely
and immediately plant available.
(ii) The pool ofP exchangeable between 1 minute and 3 months (Eimin-sn) corresponds
to the quantity of phosphate exchangeable during a period equivalent to the time of
active P uptake by the entire root system of an annual crop.
(iii) The pool ofP which can not be exchanged within 3 months (E>3m) represents forms
of P which are not readily available to plants.
The P content of Eimin_3m pools is calculated using equation [4] while the P content of
E>3m pool is calculated as the difference between the total inorganic P and the amount of
P exchangeable within 3 months (E3m).
The isotope exchange kinetics method provides information on: (i) the quantity of
isotopically exchangeable P [E(t)] which gives information on the quantity factor, and
(ii) the R/ri ratio which corresponds to the capacity factor. Simultaneously, the
phosphate concentration in the soil solution (Cp) which corresponds to the intensity
factor, is determined.
Harvest andplant analyses
The crop rotations are shown in Table 1.3. The harvested area varied between years,
depending on the crops. For cereals, the harvested area was 1.32 m x 7 m, for maize and
potato 1.5 m x 7 m, for grassland in crop rotations 1.5 m x 6.75 m, and for permanent
grassland 1.25 m x 5 m. Dry matter and P content of each crop component (aerial parts
for maize, wheat, barley, soybean, rape; aerial parts and tubers and roots for
respectively potato and beet) and of each grass cut (aerial parts) were determined for
each treatment and each year. The P content in plant material was determined using
colorimetry (Murphy and Riley, 1962) after calcination of 5g plant material (2h at
450°C) and subsequent solubilization of the ashes in 7.5ml concentrated (37%) HCl and
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 35
5 ml HF (40%). The P balances were calculated by cumulating the yearly fertilizer
inputs and subtracting the cumulated P uptake by crops. P uptake was calculated from
yields and P contents of all the harvested crop components.
Statistics
Specificity oflong-termfield experiments
Some difficulties may arise when working with data from long-term field experiments:
(i) some informations or observations may be missing, (ii) the measurements can be
difficult to interpret, because the treatments effects may develop very slowly with time
and large variations between years can be observed (Jaakola et al., 1997), especially for
yields because of different conditions in the growing season (Rubœk, 2000), (iii) the
trial design and decision about measurements were often made by someone else several
years ago, and the objectives for the experiment now may be different from those
decided at the beginning, (iv) statistical methods used today does not correspond exactly
to the old experimental design. These specific experiments have to be carefully
statistically analyzed, because data recorded from the same plots through several years
are correlated, and there are few replications for the different treatments studied. These
various statistical difficulties may be overcome by choosing an appropriate statistical
analysis.
Yields: Except for the Vaz grassland, the crop rotations included more than one crop.
Thus, to perform statistical analyses on time series of yield from variable crops, the dry
matter yield each year was expressed as the percentage of the yield obtained on the P
treatment (relative yield), assuming that the yield obtained from this treatment was the
optimal yield for the analyzed crop and soil type. The effect of P fertilization on crop
yields and P uptake was tested with an ante-dependence analysis of covariance (Ersb0ll,
1994; Kenward, 1987; Rubaek, 2000) on the relative yield and performed with the
MIXED procedure of the SAS software (SAS Institute, Cary, NC, USA, version 8,
2000). In this modified multivariate analysis, the measurement of the previous year was
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 36
included as covariate making possible the differentiation of the time profiles between
treatments.
Soil analysis: Comparisons of P availability parameters measured between 1989 and
1993 or 1989 (1993 for Changins) and 1998 for each treatment were performed using
the T-TEST procedure with paired comparisons (SAS, 2000), because measurements on
the same plots were not independent. Treatment effects in 1998 were detected for each
site by performing one-way analysis of variance (ANOVA) with the GLM procedure of
the SAS software. Means were compared with the Duncan's multiple range test;
statistical significance indicated at the 0.05 probability level. Linear regressions were
performed using the REG procedure of the SAS software.
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 37
Results and discussion
Yields
The mean, minimum and maximum yields obtained for the different crops of the
studied rotations are presented in the Table 1.4.
Table 1.4. Mean, minimum and maximum yields obtained in the seven field experiments
over all years and treatments for the main crop components
crops component mean yield minimum maximum
tha"1
beet roots 18.9 9.6 29.0
maize grains 8.1 1.1 11.5
potato tubers 6.9 2.2 12.3
soybean grains 3.3 2.9 3.7
wheat grains 5.2 2.0 6.9
barley grains 6.9 5.2 8.4
rape grains 2.5 1.3 3.7
grassland R all cuts 11.7 6.1 17.4
grassland P all cuts 7.6 4.2 10.7
The ante-dependence analysis performed for all sites from 1989 to 1998 showed that no
significant differences in yields were observed between the three treatments (OP, P,
P>exp) at six from the seven trials (Table 1.5). The relative yields compared to the P
treatment are shown in the Figure 1.1 for the Cadenazzo trial. The yields observed in the
OP treatment at Rümlang are since 1994 significantly lower than those observed in the
two other treatments (P and P>exp) (Figure 1.2). The first crop on which a yield
decrease was observed in the absence of P fertilization was potato that is known for its
high requirements in nutrients (Greenwood et al., 1980; Khiari et al., 2000). The results
obtained in our study agree with those of previous works showing that for diverse soil
types and crop rotations under European conditions, the omission of P fertilization for
periods shorter than 10 years has little effect on crop yield (Boniface and Trocmé, 1988;
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 38
Figure 1.1. Relative yields for the main crops components expressed as percentage of
the yields obtained on the P treatment in the Cadenazzo site from 1990 to 1998.
180
160
140
^ 120
S
2 100
<u
I 80
*60
40 -
20
0
-- OP
-
—— p
-•- 5/3P
-/\
mr^^Jm~ —è—**
1990 1992 1994
years
1996 1998
Figure 1.2. Relative yields for the main crops components expressed as percentage of
the yields obtained on the P treatment in the Rümlang site from 1990 to 1998.
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 39
Rubaek, 2000; Ellmer et al., 2000; Jungk et al., 1993; Gransee and Merbach; 2000).
Stumpe et al. (1993) reported also that alfalfa, potato and sugar beet showed the highest
yield decreases after 20 years without P fertilization in a Phaeozem soil.
Table 1.5. Results of the ante-dependance analysis performed for the period 1989-
1998 in all sites for yields of main crop components and total plant P uptake.
Experimental site Effect of P fertilisation Effect of P fertilisation
on yields on P uptake
Rümlang *
FAL n.s.
Ellighausen n.s.
Oensingen n.s.
Cadenazzo n.s.
Changins n.s.
Vaz n.s.
* indicates significance at p < 0.05
** indicates significance at p < 0.01
n.s. indicates no significance at p < 0.05
P uptake andPconcentration in different crop species
The ante-dependence analysis performed for all sites from 1989 to 1998 showed that no
significant differences in P uptake were observed between the three treatments (OP, P,
P>exp) at five of the seven sites (Table 1.5). After nine years, the treatment OP resulted
in lower P uptake only in Rümlang and Vaz while the P and P>exp treatments gave
similar results (Table 1.5, Figures 1.3 and 1.4). The first statistically significant
difference in P uptake between OP on one side and P and P>exp on the other side was
observed in 1992 in Rümlang for maize. In the permanent grassland trial at Vaz, very
large differences in P uptake were observed between OP on the side and P and P>exp
**
n.s.
n.s.
n.s.
n.s.
n.s.
**
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 40
Figure 1.3. P uptake at Rümlang from 1990 to 1998.
Figure 1.4. P uptake at Vaz from 1990 to 1998.
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 41
since 1993. This observation was consistent with that of Castillon (1991), who showed
that yield decrease and reduction in P uptake in permanent grasslands receiving no P
could be observed very quickly even on soils with high available P levels. Certain
grassland species such as Trifolium repens are known for their higher P requirements
than grasses (Dunlop and Hart, 1987; Caradus, 1990; Chapter 3 of this thesis).
However, changes in botanical composition of the grassland observed during the trial
did not explain this reduction in P uptake in the OP treatment. At the beginning of the
trial, the grassland had 32% dicotylédones, 60% grasses and 6% legumes. In the OP
treatment after 9 years of trial, the dicotylédones had increased by 8% while the
proportion of grasses decreased and the proportion of legume remained constant. The
botanical composition was not affected in the two other treatments (P and P>exp).
The P concentrations in the harvested plant parts (Table 1.6) were in the range of the
reference values given for Switzerland (Walter et al, 1994).
Table 1.6. Mean P concentrations determined for the main crop components over all sites,
years and treatments, compared to the reference concentrations given by Walter et al.
(1994).
crops component mean concentration reference concentrations
g kg"1 Dry Matter
beet roots 1.98 1.74-2.62
maize grains 2.88 1.74-3.49
potato tubers 2.73 0.44 -0.87
soybean grains 6.01 4.36 -7.85
wheat grains 4.05 2.83 - 3.92
barley grains 4.29 3.05 - 3.92
rape grains 6.99 5.67 - 8.28
grassland R first cut 3.64 3.05 - 3.92
grassland P first cut 2.31 2.40- 3.49
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 42
Concentrations below the references were only observed for maize in 1996 and for
rapeseed in 1998 at Changins OP and for grassland in 1996 at Rümlang OP. Fertilization
(P>exp treatment) increased the P concentration in potato in Cadenazzo and Rümlang,
and in rapeseed in Changins, otherwise, the effects of P>exp on the P concentration of
crops remained limited. This is consistent with other studies showing that in European
agroecosystems different P fertilization regimes had little effect on the P content in
cereal grains (Jaakola et al., 1997) or on shoot P concentrations (Jungk et al., 1993)
during at least the first ten years of trial. The climatic conditions have a higher impact
on crop P concentration than the P fertilization (Jaakola et al., 1997; Boniface and
Trocmé, 1988). For the permanent grassland, values on the OP treatment were almost
always under the reference concentration range.
P balances
The 3 P fertilization regimes resulted at all sites in different P balances both in 1993 and
in 1998 (Table 1.7). These balances were negative for the OP treatment and positive for
both the P and the P>exp treatments. By 1998, the balance observed in the OP treatment
demonstrated that soils had been able to deliver 88 to 144 mg P kg"1 soil without
significant effect on crop yield in 6 of the seven trials. This ability of plants to mobilize
P in freshly non-fertilized soils has been observed in all long-term field experiments
conducted in Western Europe. Ellmer et al. (2000) showed that even after 60 years of
trial 16 kg P ha"1 year"1 could still be mobilized by a rotation spring barley-potato-maize
in a sandy soil. The positive balance observed in the P treatment showed that the P
taken up by the plants was lower than the applications, even though this treatment was
meant to compensate the crop exportations. The P surplus in the P>exp treatment had
no effect on crop yields.
Changes in total, inorganic and organic P
Changes in Pi, Po and Pt with time. The OP treatment led to a significant (p<0.05)
decrease in the total P content of the 0-20 cm horizon between 1989 and 1998 in
Cadenazzo, FAL, Ellighausen and Rümlang and to a significant (p<0.05) decrease in
inorganic P in Cadenazzo, FAL, Ellighausen and Oensingen (Table 1.8). Significant
decreases of total and mineral P between 1989 and 1993 were only observed in the 0-20
I. Effect of P input/output regime on soil P exchangeability, crop yields and P uptake 43
Table 1.7. Cumulative P balances in mg P kg"1 soil in 1993 and 1998 for all
sites and treatments, calculated as the difference between the cumulative P
inputs and the cumulative P uptake.
Experimental site treatment 1993 1998
OP -32 c* -61 C
Rümlang P 4 B 17 B
P > exp 33 A 82 A
OP -48 C -91 C
FAL P 2 B 19 B
P > exp 39 A 102 A
OP -64 C -113 C
Ellighausen P 0 B 11 B
P > exp 42 A 95 A
OP -62 C -119 C
Oensingen P 5 B 8 B
P > exp 45 A 87 A
OP -38 C -88 C
Cadenazzo P 3 B 6 B
P > exp 31 A 71 A
OP -124 C -144 C
Changins P 116 B 134 B
P > exp 287 A 347 A
OP -51 C -121 C
Vaz P 58 B 84 B
P > exp 118 A 208 A
*Different higher case letters for the same site indicate a statistically significantdifference between treatment at the 5% probability level by the Duncan's
