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Rock phosphate combined with phosphate-solubilizing microorganisms and humic substance for reduction of plant phosphorus demands from single superphosphate

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Validoro Bazoni Giro at State University of Norte Fluminense
Validoro Bazoni Giro
Keiji Jindo at Wangeningen University
Keiji Jindo
  • Wangeningen University
Cássio Vittorazzi at State University of Norte Fluminense
Cássio Vittorazzi
R.S.S de Oliveira
R.S.S de Oliveira
R.S.S de Oliveira
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Abstract and Figures

Phosphorus (P) plays an important role in agroecosystems as a limiting nutrient for crop production because of its low soil availability and high requirements by plants at an early stage. Soluble P-fertilizer amendments contrast with low P use efficiency in weathering tropical soils. The aim of this work was to use P-solubilizing microorganisms (PSMs) and humic substance (HS) to enhance P solubility of natural rock phosphate (RP) of Araxá for partial replacement of single superphosphate (SSP). Two pot experiments were designed under greenhouse conditions. First, defined proportions of SSP and RP were combined in the following six treatments (T1, 0/100%; T2, 20/80%; T3, 40/60%; T4, 60/40%; T5, 80/20% and T6, 100/0% SSP/RP), using two different P-placement methods (broadcast and deep placement). The sub-optimal P fertilizer combination of 40% SSP + 60% RP was selected. In addition, deep placement of the P-fertilizer combination of SSP + RP produced a better plant response for all P rates. Based on the selected proportion of SSP/RP, a second assay was performed using mixed strains of bacteria and fungi (PSM, previously selected for RP solubilization) combined with humic acid (HA). We showed that PSM + HA treatment positively stimulated root and shoot weight compared with non-inoculated plants by 17 and 22%, respectively. Despite this biomass increase, no difference was observed in P concentration, indicating an increased P use efficiency. Overall, our findings suggest that the application of both PSM and HS with RP may be a suitable method for reduction of soluble P fertilizer demands without compromising plant yields.
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ActaHortic.1146.ISHS2016.DOI10.17660/ActaHortic.2016.1146.8
Proc.IIIInt.Sym.onOrganicMatterMgt.andCompostUseinHort.
Eds.:M.Cayuelaetal.
63
Rock phosphate combined with phosphate-
solubilizing microorganisms and humic substance for
reduction of plant phosphorus demands from single
superphosphate
V.B.Giro,K.Jindo,C.Vittorazzi,R.S.SdeOliveira,G.P.Conceição,L.P.CanellasandF.L.Olivares
NúcleodeDesenvolvimentodeInsumosBiológicosparaAgricultura,UniversidadeEstadualdoNorteFluminense
DarcyRibeiro,CamposdosGoytacazes,RiodeJaneiro,Brazil.
Abstract
Phosphorus(P)playsanimportantroleinagroecosystemsasalimitingnutrient
forcropproductionbecauseofitslowsoilavailabilityandhighrequirementsby
plantsatanearlystage.SolubleP‐fertilizeramendmentscontrastwithlowPuse
efficiencyinweatheringtropicalsoils.TheaimofthisworkwastouseP‐solubilizing
microorganisms(PSMs)andhumicsubstance(HS)toenhancePsolubilityofnatural
rockphosphate(RP)ofAraxáforpartialreplacementofsinglesuperphosphate(SSP).
Twopotexperimentsweredesignedundergreenhouseconditions.First,defined
proportionsofSSPandRPwerecombinedinthefollowingsixtreatments(T1,
0/100%;T2,20/80%;T3,40/60%;T4,60/40%;T5,80/20%andT6,100/0%
SSP/RP),usingtwodifferentP‐placementmethods(broadcastanddeepplacement).
Thesub‐optimalPfertilizercombinationof40%SSP+60%RPwasselected.In
addition,deepplacementoftheP‐fertilizercombinationofSSP+RPproduceda
betterplantresponseforallPrates.BasedontheselectedproportionofSSP/RP,a
secondassaywasperformedusingmixedstrainsofbacteriaandfungi(PSM,
previouslyselectedforRPsolubilization)combinedwithhumicacid(HA).Weshowed
thatPSM+HAtreatmentpositivelystimulatedrootandshootweightcomparedwith
non‐inoculatedplantsby17and22%,respectively.Despitethisbiomassincrease,no
differencewasobservedinPconcentration,indicatinganincreasedPuseefficiency.
Overall,ourfindingssuggestthattheapplicationofbothPSMandHSwithRPmaybea
suitablemethodforreductionofsolublePfertilizerdemandswithoutcompromising
plantyields.
Keywords:humicacid,biofertilizer,organicfarming,Pdeficiency,Acrisol
INTRODUCTION
Phosphorusplaysanimportantroleinagroecosystemsasalimitingnutrientforcrop
productionbecauseofitslowsoilavailabilityandhighearlyPrequirementsbyplants(Chien
et al., 2011). However, demands for soluble P‐fertilizer sources contrast with low P use,
beingmorecriticalinsesquioxide‐richsoilswithhighlevelsofactiveAlandFe.Inthiscase,
largeamountsofsolublesourcesofphosphatefertilizersareneededtoovercometheirhigh
P‐fixationcapacity,wherePisconvertedintoaformunavailableforplantuptake(Zhang et
al.,2003).
OnepossibleapproachforPsupplytocropsistoincludeintegrative management
practices that would increase soil organic matter and combine organic and inorganic P
sourceswithdifferentsolubilitytraitsinordertoobtainoptimalcropyield.IglesiasJimenez
etal.(1993)evaluatedtheeffectivenessofcompostasaPsource compared with soluble
inorganicPformsandobservedanincreaseinplanttissuePconcentrationwhentheorganic
Psourcewasused.Inthiscase,organicmatterapplicationcombinedcompetitiveadsorption
effects with net mineralization of organic P that resulted in a greater residual effect on P
supply.However,theuseoforganicsourcesisassociatedwitha relatively slow
mineralization process, non‐synchronized P availability and physiological requirement at
64
theearlyphaseofplantgrowth.
Bycontrast,fullyacidulatedinorganicPfertilizers(i.e.,superphosphates)thatremain
themajorsourceofPapplicationusedbyfarmersaroundtheworld have exhibited a
negativeeconomicandecologicalimpactindifferentagricultureecosystems(Renner,2008).
Inaddition,inmostdevelopingcountries,superphosphatesarenotproducedlocally,andthe
supplytopoorfarmersisratherlimited.Thesecountriespossessdepositsofrockphosphate
(RP)thatcanbeusedfordirectapplicationinagriculture,beingconsideredasanagronomic
andeconomicallyattractivealternative(Zhangetal.,2003).
Selected P‐solubilizing microorganisms (PSM), technologically developed as
bioinoculants (Duarah et al., 2011; Nahas, 1996; Stamford et al., 2008), can be useful to
improve PR solubility. PSMs are ubiquitous inhabitants of soil,mainlyrepresentedby
bacteria and fungi groups. The biomineralization activity on RPismainlyattributedto
production of organic acid and subsequent lowering of pH, although other mechanisms
could operate, such as exopolysaccharide production (Nahas, 1996; Oliveira et al., 2009).
PSMconsortiumsofferthe advantageofmoreefficientP‐solubilizationcapacitythansingle
species,evencomparabletosolublePsources(BrazandNahas,2012).Othertechnological
approaches to increase RP solubilization involve bioreactors for confined reactions, using
differentcarbonand/ornitrogensourcestosupportmicrobialpopulationsandactivitysuch
as biochar (Mendes et al., 2014), agro‐industrial waste (VassilevandVassileva,2003)and
immobilizedcelltechnology(Vassilevetal.,2001).
TheaimofpresentworkwastoassesstheeffectofutilizationofRPasasubstitutefor
singlesuperphosphate(SSP)andthepotentialofmicroorganismsin thepresenceofhumic
acid(HA)onPsolubilizationandplantgrowth.CombinedapplicationofHAandPSMshave
been successfully used as a new biofertilizer for different crops (Canellas et al., 2013;
Canellasand Olivares,2014;Olivaresetal.,2015). It hasbeendemonstratedthatHAhasa
protectiveeffectonmicroorganisms(Martinez‐Balmorietal.,2013),andtherootexudation
profileofplantstreatedwithHAdisplayschangesintheeffluxof organicacids(Canellaset
al.,2008).
WeinitiallydefinedtheproperPratioinacombinationofSSPandRPthatcan
potentially achieve the maximum SSP dose, evaluating as well the effect of two different
typesofPlocalizationonplantgrowth.Subsequently,weevaluatedbioinoculant,formulated
with PSMs in combination with HA, as a new biological input for reduction of plant P
demandsintheformofSSP.
MATERIALSANDMETHODS
Experimentdesign1
Hybridmaizeseeds‘DKB789’wereplantedinplasticpotsfilledwith yellow Acrisol,
whichis one of the typicaltropical weathering acid soils in Brazil with low availableP, low
soilorganicmatter(SOM)content,loweffectivecation‐exchangecapacityandhighP‐fixation
capacity. The chemical characteristicsofthe Acrisol before and after 30 daysof incubation
withdolomitelimestonecanbenotedin(Table1).TheRPofAraxá (33% P2O5; particles
smallerthan0.044mmorsieveof325mesh)wasmixedhomogeneously with SSP. The
mixtureofSSP/RPwasappliedaccordingtotherecommendeddose of 0.14 g of P2O5kg‐1
Acrisol.Sixtreatmentsofthedifferentproportionrates(SSPandRP)weresetup:1)0%SSP
+100%RP;2)20%SSP+80%RP;3)40%SSP+60%RP;4)60%SSP+40%RP;5)80%SSP
+20%RP;6)100%SSP+0%RP.Inaddition,othermacronutrients(NandK)wereapplied
equally to the soil. Each different treatment was performed in four replicates with
randomized statistical design. TheeffectofthePlocationwasalsoevaluatedwith
broadcastingapplicationanddeepplacementbeyondtheseedsowing.After30daysunder
greenhouseconditions,dryweight(shootandroot),rootvolume(RV)androot:shootratio
weremeasured.Equationsofthepolynomialregressionmodeland the correlation
coefficientanalysis(R2)weremeasuredwiththeplottingprogramSIGMAPLOT,basedonthe
FtestattheP<0.05probabilitylevel.
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Table1. Chemical analysisofB‐horizon of yellow Acrisol soil beforeandafterlimingwith
dolomitelimestone.SB,Sumofbase;CEC,cation‐exchangecapacity.
C
(g kg-1) pH P
(mg dm-3)
K
(mg dm-3)
Ca2+ Mg2+ Al3+ H+Al SB CEC
(cmolc dm-3)
4.7 5.1 4 74 0.5 0.8 0.2 2.0 1.8 3.8
3.9 6.4 4 220 1.1 0.6 0.0 1.0 2.4 3.4
SB, Sum of base; CEC, cation-exchange capacity.
Experimentdesign2
Basedontheresultsoftheprevioustrial,anewpotexperimentwiththesame
experimental design was set up, emended with the sub‐optimal mixtureofPsourcesof
SSP/RP(40:60)andinoculatedornotwithPSMsincombinationor not with HA, in a
completely randomized designed with three treatments and four replicates. After 30 days
under greenhouse conditions, dry weight (shoot and root) and RV were measured. The
determinationofPconcentrationinplanttissuewasmeasuredby using a
spectrophotometerafterdigestionwithsulfuricacid.ThePSMbioinoculantwasformulated
asamicrobialconsortiumusingtwobacteriaandtwofungipreviouslyselectedforhighRP‐
solubilizationability (Table2)insolidandliquidmedium (Vermaetal.,2001),modifiedby
the introduction of Araxá RP. The bacterial inocula (strains BAC22andBAC14H)were
obtainedfromculturesthathadbeengrowninliquidDygsmediumat30°Cfor2daysat140
rpminarotatoryshaker (Baldani et al., 2014). The bacterial suspensions werecentrifuged
at2,000×g,resuspendedinsterilizedwaterandadjustedtoanopticaldensityof1.0at460
nm, which is equivalent to 108cellsmL
‐1.Thefungalinocula(strainsF5andF309)were
grownonsolidpotatodextroseagar(PDA)medium at 30°C for7days.Afterthat,10mLof
sterile water was added. The suspensions obtained werecounted inaNeubauerchamber
andadjustedto3×105sporesmL‐1.Allthemicroorganismsuspensionsweremixedatequal
volumeandappliedtogetherwiththeHA(20mgL‐1 of C)aroundthe localized Pfertilizer
mixture. The volume of the microbial consortium suspension was such that the final
substratemoisturewas50%.TheHAwasobtainedfromfiltercakesugarcanevermicompost
(Canellasetal.,2002).AllresultsarereportedasmeanswithstatisticalanalysisofFtestfor
varianceandFisher‐LCDtestattheP<0.05probabilitylevel.
Table2. CharacteristicsofthefourPSMsusedasbioinoculantinthepresentstudy.
Microorganism Strain number Taxonomy Origin
Bacterium BAC22 Serratia marcescens Vermicompost
Bacterium BAC14H Burkholderia sp. Soil (20-40 cm)
Fungus F5 Curvularia senegalensis Vermicompost
Fungus F309 Unidentified Vermicompost
RESULTSANDDISCUSSION
Experiment1
Theeffect of the differentproportionsof SSP/RP on plant growthandP locationare
showninFigure1.Asexpectedforsesquioxide‐richsoilswithhighlevelsofactiveAlandFe,
broadcastingPincreasedtheinteractionwiththeadsorptiveclaysurface,probablyreducing
Pavailabilityinthesoilsolution,andconsequentlyreducedthe growth rate response to
increaseddosesofappliedPfertilizer(Wisawapipatetal.,2009).Contrarily,deepplacement
ofthePfertilizerincreasedallbiometricparametersofthe plantresponses,comparedwith
thebroadapplication,resultinginaclearplantresponsetoincreaseddosesofSSP.
66
Figure1. Shootdryweight(g),rootdryweight(g),rootvolume(cm3),androot/shootratio
ofmaizecultivar‘DKB789’grownwithdifferentproportionsof SSP/RP and P
placement.
Concerning different proportions of SSP:RP, plant growth was increased in those
treatmentswithahighSSPproportion(100:00,80:20,60:40). On the contrary,alowplant
growth response was shown with a high RP proportion (0:100, 20:80), probably due to a
consequenceofinsufficientacidityinthesoilforsolubilizationandlimitedPsink,(Chienet
al.,2011).Thetreatmentof40:60(SSP:RP)producedhighrootproliferation(Figure1)with
respecttoothertreatments,eventhoughnosignificantdifferenceinshootproliferationwas
observed. Considering that root development is a key factor forimprovingsoilvolume,a
proportion of 40:60 was chosen for the next experiment aimed at minimizing the SPP
demandofplantsbyexploringthepotentialofPSMandHAcombination.
Experiment2
The impact of the combined application of PSMs and HA on plant growth was
observedinshoot(SDW)androotdryweight(RDW)(Figure2)using the 40:60 SSP/RP
combination of localized P fertilizer selected from Experiment 1. Interestingly, the
inoculationwithPSMswasonlyeffectiveinthepresenceofHA,increasingSDWandRDWby
17 and 22%, respectively, compared with treatment T1 (only P fertilizer). Enhanced
performance of plant‐growth‐promoting microorganisms in the presence of humic
substances has been reported previously, and a generation of new biological inputs for
agricultureproposed(Busatoetal., 2012;Canellasetal.,2013;CanellasandOlivares,2014;
Olivareset al., 2015). Humicsubstance not only enhancestheP availabilitybyrhizosphere
acidification(Canellasetal.,2008),butalsoinhibitsPfixationinsoilparticles,makinglabile
P forms available for more time for plant uptake and metabolic use (Erro et al., 2012).
However,higherPconcentrationwasfoundonlyinthe rootsintreatmentT3(Pfertilizer +
PSMandHA),andnodifferencewas found in shoots (Figure2) related tothe control(T1).
According to a previous report of PSM and HA application (Winarso et al., 2011), a weak
correlationofmacronutrientsinsoybeanshootswasobserved.TheapplicationofPSMalone
67
(T2) produced lower values for all parameters of plant growth measured (Figure 2). A
higherratioofroot/shootintreatmentT2reflectsthegeneral morphological changes
causedbyPdeficiencyduetopreferentialdistributiontotheroots(Wissuwaetal.,2005).In
addition,itisshouldbepointedoutthatavailabilityofothernutrientsinfluencePSMgrowth
andstimulatesPconsumption(Mendesetal.,2014).Hence,thepresenceofHA(T3)
providesfavorableconditionsformicroorganisms(Martinez‐Balmorietal.,2013).
Figure2. Shootdryweight(g),rootdryweight(g),rootvolume (cm3),root/shootratio,
shootphosphoruscontent(mgplant‐1)androotphosphoruscontent(mgplant‐1)
ofmaizecultivar‘DKB789’.Means(±SE)followedbythesameletters do not
differsignificantlyaccordingtomeanseparationbyF‐testatthe P<0.05
probabilitylevel.
CONCLUSIONS
ThereispotentialforthereductionofsolublePfertilizerdemandsbyapplicationofRP
incombinationwithselectedPSMsinthepresenceofHA.Thisinitiative can be improved
especiallybylocalizedPapplication,wherethesolubilizationconditionswouldbeoptimized
forplantgrowthbyamoredefinedenvironment,closetotherhizospherecompartment.
ACKNOWLEDGEMENTS
ThankstoCNPq,CAPES,FAPERJandINCTforBiologicalNitrogenFixation for the
fellowshipsandgrantsthatfundedthisresearch.
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... Among them is the design of a consortium with elite strains of bacteria and fungi and combining proper PSM bioinoculant formulation and delivery. The most relevant approach is for PSM to be combined with rock phosphates and stable OM or its fractions (i.e., HA and FA) to reduce P-adsorption and precipitation on the mineral lattice [3,7,30,70,77]. Microbial formulations combining P-solubilizing and P-mineralizing properties have been proposed in association with OM and slow-release mineral P-sources [7,11,30,77] as a suitable P-fertilizer complementary to fully acidulated inorganic P-sources. Reductions in phytoavailable P source application rates (e.g., single superphosphate, SSP) can be achieved without compromising crop productivity. ...
... The most relevant approach is for PSM to be combined with rock phosphates and stable OM or its fractions (i.e., HA and FA) to reduce P-adsorption and precipitation on the mineral lattice [3,7,30,70,77]. Microbial formulations combining P-solubilizing and P-mineralizing properties have been proposed in association with OM and slow-release mineral P-sources [7,11,30,77] as a suitable P-fertilizer complementary to fully acidulated inorganic P-sources. Reductions in phytoavailable P source application rates (e.g., single superphosphate, SSP) can be achieved without compromising crop productivity. ...
... Reductions in phytoavailable P source application rates (e.g., single superphosphate, SSP) can be achieved without compromising crop productivity. For example, Giro et al. [30] applied 60% of rock phosphate and 40% of SSP and, combined with MSP and HA, showed increased maize biomass by ~ 20% compared to plants that received the fertilizer. ...
Biotic and abiotic effects of soil organic matter on the phytoavailable phosphorus in soils: a review Chemical and Biological Technologies in Agriculture
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  • Mar 2023
Soil organic matter (SOM) has a critical role in regulating soil phosphorus (P) dynamics and producing phytoavailable P. However, soil P dynamics are often explained mainly by the effects of soil pH, clay contents, and elemental compositions, such as calcium, iron, and aluminum. Therefore, a better understanding of the mechanisms of how SOM influences phytoavailable P in soils is required for establishing effective agricultural management for soil health and enhancement of soil fertility, especially P-use efficiency. In this review, the following abiotic and biotic mechanisms are discussed; (1) competitive sorption between SOM with P for positively charged adsorption sites of clays and metal oxides (abiotic reaction), (2) competitive complexations between SOM with P for cations (abiotic reaction), (3) competitive complexations between incorporation of P by binary complexations of SOM and bridging cations with the formation of stable P minerals (abiotic reaction), (4) enhanced activities of enzymes, which affects soil P dynamics (biotic reaction), (5) mineralization/immobilization of P during the decay of SOM (biotic reaction), and (6) solubilization of inorganic P mediated by organic acids released by microbes (biotic reaction). Graphical Abstract
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... The results showed an increase in the shoot and root weight of plants compared with the noninoculated treatment. The findings suggested an increase in the efficiency of P use and that the application of PSM and HSs can become an alternative to reduce the use of soluble P fertilizers without harming plant yield (Giro et al., 2016). A recent study also ...
Humic Substances in Combination With Plant Growth-Promoting Bacteria as an Alternative for Sustainable Agriculture
Article
Full-text available
  • Oct 2021
Plant growth-promoting bacteria (PGPB) and humic substances (HSs) are promising options for reducing the use of pesticides and mineral fertilizers. Although many studies have shown the effects of PGPB and HSs separately, little information is available on plant responses to the combined application of these biostimulants despite the great potential for the simultaneous action of these biological inputs. Thus, the objective of this review is to present an overview of scientific studies that addressed the application of PGPB and HSs to different crops. First, we discuss the effect of these biostimulants on biological nitrogen fixation, the various effects of the inoculation of beneficial bacteria combined with the application of HSs on promoting the growth of nonleguminous plants and how this combination can increase bacterial colonization of plant hosts. We also address the effect of PGPB and HSs on plant responses to abiotic stresses, in addition to discussing the role of HSs in protecting plants against pathogens. There is a lack of studies that address the role of PGPB + HSs in biocontrol. Understanding the factors involved in the promotion of plant growth through the application of PGPB and HSs can assist in the development of efficient biostimulants for agricultural management. This approach has the potential to accelerate the transition from conventional cultivation to sustainable agrosystems.
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... In addition to their native P solubilizing capacity in soils, PSB can be combined to RP, as both are natural resources and their co-application has been demonstrated to improve RP agronomic efficiency [27][28][29][30]. Indeed, exploitation of microbial functional traits related to P solubilization, mainly in high P-retention agricultural soils, is paramount in order to propose microbial-based strategies enabling RP use efficiency, [31]. ...
Phosphate bacterial solubilization: A key rhizosphere driving force enabling higher P use efficiency and crop productivity
Article
Full-text available
  • Aug 2021
Background Increasing crop production to feed a growing population has driven the use of mineral fertilizers to ensure nutrients availability and fertility of agricultural soils. After nitrogen, phosphorus (P) is the second most important nutrient for plant growth and productivity. However, P availability in most agricultural soils is often limited because P strongly binds to soil particles and divalent cations forming insoluble P-complexes. Therefore, there is a constant need to sustainably improving soil P availability. This may include, among other strategies, the application of microbial resources specialized in P cycling, such as phosphate solubilizing bacteria (PSB). This P-mediating bacterial component can improve soil biological fertility and crop production, and should be integrated in well-established formulations to enhance availability and efficiency in use of P. This is of importance to P fertilization, including both organic and mineral P such as rock phosphate (RP) aiming to improve its agronomic efficiency in an integrated crop nutrition system where agronomic profitability of P and PSB can synergistically occur. Aim of Review The purpose of this review is to discuss critically the important contribution of PSB to crop P nutrition in concert with P fertilizers, with a specific focus on RP. We also highlight the need for PSB bioformulations being a sustainable approach to enhance P fertilizer use efficiency and crop production. Key Scientific Concepts of Review We first recognize the important contribution of PSB to sustain crop production, which requires a rational approach for both screening and evaluation of PSB enabling an accurate assessment of the bacterial effects both alone and in intertwined interaction with plant roots. Furthermore, we propose new research ideas about the development of microbial bioformulations based on PSB with a particular focus on strains exhibiting synergetic effects with RP.
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... This enabled higher fixation of atmospheric N and solubilization of soil P compounds, resulting in higher root nutrient uptake. Similar effects were observed for the uptake of N (Canellas et al., 2013) and P in corn (Giro et al., 2016). ...
Application of biofertilizer in degraded pasture modified C dynamics and improved forage yield in a short-term period at the tropical region
Article
  • Dec 2020
Recovery of degraded pastures improves the sustainability of meat and milk production systems. Humic acids (HA) and endophytic diazotrophic bacteria (EDB) are known to have bio-stimulating effects on several crops but have not been tested for the recovery of degraded pastures. The aim of the present study was to evaluate soil C and N dynamics, nutrient uptake and forage yield of Brachiaria decumbens following the foliar application of HA and EDB in a degraded pasture. A randomized block design with six replications was used. The four treatments were: HA, EDB, HA+EDB and Control. The subplots consisted of four evaluation times for soil characteristics: before treatment application (0) and 30, 60 and 120 days after treatment application (ATA). Soil total organic carbon (TOC), recalcitrant carbon (Crecal), labile carbon (Clabil), total nitrogen (TN) and C and N stocks were determined in the 0-5, 5-10, 10-20 and 20-40 cm of soil layers. Forage yield and leaf nutrient contents were evaluated at 30 days ATA. The application of the HA and EDB increased the TOC, Clabil, soil C stock (≈18%), forage dry matter yield (16 to 52%) and nutrient uptake (≈30%) after 30 days ATA. Our results showed that the application of HA combined with EDB may be a strategy for the recovery of degraded pastures in the tropical region.
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... Combinatory use of PSB and rock phosphate (RP) that are considered to be natural resources has been successful through a number of applied research investigations that demonstrated an improved agronomic RP efficiency (Gomes et al., 2014;Abbasi et al., 2015;Giro et al., 2016;Bargaz et al., 2018). Exploitation of microbial functional traits related to P solubilization is paramount as to propose microbial-based strategies enabling increased RP use efficiency required in many high P-retention agricultural soils (Kumar, 2016). ...
Phosphate Solubilizing Rhizobacteria Could Have a Stronger Influence on Wheat Root Traits and Aboveground Physiology Than Rhizosphere P Solubilization
Article
Full-text available
  • Jul 2020
Limited P availability in several agricultural areas is one of the key challenges facing current agriculture. Exploiting P-solubilizing bacteria (PSB) has been an emerging bio-solution for a higher rhizosphere P-availability, meanwhile the above- and below-ground interactions that PSB would trigger remain unclear over plant growing stages. We hypothesized that PSB effects on plant growth may be greater on root traits that positively links with aboveground physiology more than the commonly believed rhizosphere P bio-solubilization. In this study, five contrasting PSB (Pseudomonas spp.) isolates (low “PSB1”, moderate “PSB2 and PSB4” and high “PSB3 and PSB5” P-solubilizing capacity “PSC”) were used to investigate above- and below-ground responses in wheat fertilized with rock P (RP) under controlled conditions. Our findings show that all PSB isolates increased wheat root traits, particularly PSB5 which increased root biomass and PSB3 that had greater effect on root diameter in 7-, 15- and 42-day old plants. The length, surface and volume of roots significantly increased along with higher rhizosphere available P in 15- and 42-day old plants inoculated with PSB4 and PSB2. Shoot biomass significantly increased with both PSB2 and PSB5. Root and shoot physiology significantly improved with PSB1 (lowest PSC) and PSB4 (moderate PSC), notably shoot total P (78.38%) and root phosphatase activity (390%). Moreover, nutrients acquisition and chlorophyll content increased in inoculated plants and was stimulated (PSB2, PSB4) more than rhizosphere P-solubilization, which was also revealed by the significant above- and below-ground inter-correlations, mainly chlorophyll and both total (R = 0.75, p = 0.001**) and intracellular (R = 0.7, p = 0.000114*) P contents. These findings demonstrate the necessity to timely monitor the plant-rhizosphere continuum responses, which may be a relevant approach to accurately evaluate PSB through considering below- and above-ground relationships; thus enabling unbiased interpretations prior to field applications.
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... The PL and RP interaction effects were not detected by changes in the P and N concentrations in maize diagnostic leaves (Table 1), suggesting that there was greater efficiency in fresh shoot matter production and the dry matter of leaves + stems and cobs with the application of PL+RP (Figure 1). Giro et al. (2016) reported increases in the dry matter of maize shoot and roots without, however, increasing P concentrations in both, were no differences between the treatments in the dry matter yields of the cobs. In the fall treatment applications, PL+RP increased the cob dry matter yields by 12 % compared to the C, 20 % compared to the PL, 28 % compared to the RP and 12 % compared to the PL+RP+M. ...
Maize yields and carbon pools in response to poultry litter, rock phosphate and P-solubilizing microorganisms
Article
Full-text available
  • Jan 2020
  • SCI AGR
The acid release of phosphates from rock phosphates (RP) and the retention of ammonium by inorganic phosphates have been studied separately in composting; however, there is a gap in the knowledge of combined application of RP with organic residues and microorganisms. The objectives were to evaluate the combined application of fresh poultry litter (PL) with RP and P-solubilizing microorganisms (M) on soil organic matter pools, microbial biomass C (MB-C) and on whole-plant silage maize and grain yields. Two field experiments tested the effects of timing of applications of PL (8 Mg ha–1), RP (4 Mg ha–1) and microorganisms on soil organic matter pools, nutritional aspects and productive components of maize crop whole-plant silage. A second experiment evaluated the effects of RP doses (0, 3, 6 and 9 Mg ha–1) with a fixed dose of PL (8 Mg ha–1) on maize grains. Application of PL+RP decreased soil organic C, while RP alone increased the humin fraction C compared to the control. The MB-C in soil with PL and PL+RP+M increased in comparison to the control and the RP. The application of PL, based on an average of fall and spring, increased leaves + stem dry matter, while in the fall on its own, the highest cob yield was observed in the combination of PL+RP, showing synergistic effects. The best ratio of poultry litter to rock phosphate combination is 2:1 in the anticipated fall application on the maize silage crop or immediate application on the maize grain crops.
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... Despite this biomass increase, no difference was observed in P concentration, indicating an increased P use efficiency. The application of both PSM and HS with RP may be a suitable method for reduction of soluble P fertilizer demands without compromising plant yields [25]. Results described in the literature show a promising use of humic substances to improve the benefit of phosphorus solubilizing microorganism [26]. ...
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From Lab to Field: Role of Humic Substances Under Open-Field and Greenhouse Conditions as Biostimulant and Biocontrol Agent
Article
Full-text available
  • May 2020
The demand for biostimulants has been growing at an annual rate of 10 and 12.4% in Europe and Northern America, respectively. The beneficial effects of humic substances (HS) as biostimulants of plant growth have been well-known since the 1980s, and they can be supportive to a circular economy if they are extracted from different renewable resources of organic matter including harvest residues, wastewater, sewage sludge, and manure. This paper presents an overview of the scientific outputs on application methods of HS in different conditions. Firstly, the functionality of HS in the primary and secondary metabolism under stressed and non-stressed cropping conditions is discussed along with crop protection against pathogens. Secondly, the advantages and limitations of five different types of HS application under open-fields and greenhouse conditions are described. Key factors, such as the chemical structure of HS, application method, optimal rate, and field circumstances, play a crucial role in enhancing plant growth by HS treatment as a biostimulant. If we can get a better grip on these factors, HS has the potential to become a part of circular agriculture.
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agronomy Interaction between Humic Substances and Plant Hormones for Phosphorous Acquisition
Article
Full-text available
  • May 2020
Phosphorus (P) deficiency is a major constraint in highly weathered tropical soils. Although phosphorous rock reserves may last for several hundred years, there exists an urgent need to research efficient P management for sustainable agriculture. Plant hormones play an important role in regulating plant growth, development, and reproduction. Humic substances (HS) are not only considered an essential component of soil organic carbon (SOC), but also well known as a biostimulant which can perform phytohormone-like activities to induce nutrient uptake. This review paper presents an overview of the scientific outputs in the relationship between HS and plant hormones. Special attention will be paid to the interaction between HS and plant hormones for nutrient uptake under P-deficient conditions.
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The art of isolating nitrogen-fixing bacteria from non-leguminous plants using N-free semi-solid media: a practical guide for microbiologists
Article
Full-text available
  • Nov 2014
Background and aim: Nitrogen-fixing bacteria or diazotrophs have been isolated for many years using different formulations of N-free semi-solid media. However, the strategies used to isolate them, and the recipes of these media, are scattered through the published literature and in other sources that are more difficult to access and which are not always retrievable. Therefore, the aim of this work was to collate the various methods and recipes, and to provide a comprehensive methodological guide and their use by the scientific community working in the field of biological nitrogen fixation (BNF), particularly with non-leguminous plants.
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Effects of humic compounds and phosphate- solubilizing bacteria on phosphorus availability in an acid soil
Article
Full-text available
This study aims at elucidating the combined effects of humic compounds and phosphate-solubilizing bacteria (Pseudomonas putida) to improve characteristics of ultisol and to increase the yields of soybean conducted in a glasshouse. The humic compounds are extracted from rice-straw compost, the phosphate-solubilizing bacteria obtained from Bogor Agricultural University, and the soil (Typic paleudult) collected from Kentrong Banten, Indonesia. The results have shown that application of humic compounds combined with inoculation of phosphate-solubilizing bacteria increases pH and available P, and decreases exchangeable Al of an ultisol. The improved soil characteristic, however, does not lead to the significant differences in the uptake of macronutrients by plant.
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Molecular characteristics of vermicompost and their relationship to preservation of inoculated nitrogen-fixing bacteria
Article
Full-text available
  • Nov 2013
  • J ANAL APPL PYROL
a b s t r a c t The chemical nature of organic matter during the process of vermicomposting of cattle manure and filter cake from a sugar factory was characterized by thermochemolysis. The pyrolysates were mainly consti-tuted of lignin moieties from propanoic acid units and short-chain (<C20) fatty acids (as methyl esters); alkanes, alkenes, terpenes and steroids were minor compounds. Nitrogen containing compounds were noticeable in filter cake vermicompost (VC) as were carbohydrate moieties. Despite thermochemolysis had shown low sensitivity for carbohydrates, the presence of a number of carbohydrate derivatives was indicative of extensive biological transformation of organic matter during vermicomposting. A high con-tent of long-chain alcohols was found only in filter cake VC. At the end of VC maturation, the content of hydrophobic compounds (lignins plus fatty acids) in filter cake residues was higher than in cattle manure. This mature VC exhibited the highest natural density of culturable diazotrophic bacteria com-pared to cattle manure VC (approximately 10 4 times cells g −1 VC), and when the diazotrophic bacterium Herbaspirillum seropedicae was introduced to both types of VC, the population numbers were higher in filter cake VC at 10 months of storage after inoculation. We found an apparent relationship between molecular characteristics of organic matter and the harboring or preservation of diazotrophic bacte-ria introduced to VC, which is a step toward understanding the relationship between the molecular characteristics of organic matter and the microbial activities.
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Physiological responses to humic substances as plant growth promoter
Article
Full-text available
  • Mar 2014
Humic substances (HS) have been widely recognized as a plant growth promoter mainly by changes on root architecture and growth dynamics, which result in increased root size, branching and/or greater density of root hair with larger surface area. Stimulation of the H + -ATPase activity in cell membrane suggests that modifications brought about by HS are not only restricted to root structure, but are also extended to the major biochemical pathways since the driving force for most nutrient uptake is the electrochemical gradient across the plasma membrane. Changes on root exudation profile, as well as primary and secondary metabolism were also observed, though strongly dependent on environment conditions, type of plant and its ontogeny. Proteomics and genomic approaches with diverse plant species subjected to HS treatment had often shown controversial patterns of protein and gene expression. This is a clear indication that HS effects of plants are complex and involve non-linear, cross-interrelated and dynamic processes that need be treated with an interdisciplinary view. Being the humic associations recalcitrant to microbiological attack, their use as vehicle to introduce beneficial selected microorganisms to crops has been proposed. This represents a perspective for a sort of new biofertilizer designed for a sustainable agriculture, whereby plants treated with HS become more susceptible to interact with bioinoculants, while HS may concomitantly modify the structure/activity of the microbial community in the rhizosphere compartment. An enhanced knowledge of the effects on plants physiology and biochemistry and interaction with rhizosphere and endophytic microbes should lead to achieve increased crop productivity through a better use of HS inputs in Agriculture.
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Biochar Enhances Aspergillus niger Rock Phosphate Solubilization by Increasing Organic Acid Production and Alleviating Fluoride Toxicity
Article
Full-text available
During fungal rock phosphate (RP) solubilization, a significant quantity of fluoride (F−) is released together with phosphorus (P), strongly inhibiting the process. In the present study, the effect of two F− adsorbents [activated alumina (Al2O3) and biochar] on RP solubilization by Aspergillus niger was examined. Al2O3 adsorbed part of the F− released but also adsorbed soluble P, which makes it inappropriate for microbial RP solubilization systems. In contrast, biochar adsorbed only F− while enhancing phosphate solubilization 3-fold, leading to the accumulation of up to 160 mg of P per liter. By comparing the values of F− measured in solution at the end of incubation and those from a predictive model, it was estimated that up to 19 mg of F− per liter can be removed from solution by biochar when added at 3 g liter−1 to the culture medium. Thus, biochar acted as an F− sink during RP solubilization and led to an F− concentration in solution that was less inhibitory to the process. In the presence of biochar, A. niger produced larger amounts of citric, gluconic, and oxalic acids, whether RP was present or not. Our results show that biochar enhances RP solubilization through two interrelated processes: partial removal of the released F− and increased organic acid production. Given the importance of organic acids for P solubilization and that most of the RPs contain high concentrations of F−, the proposed solubilization system offers an important technological improvement for the microbial production of soluble P fertilizers from RP.
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A combination of humic substances and Herbaspirillum seropedicae inoculation enhances the growth of maize (Zea mays L.)
Data
Full-text available
  • Mar 2013
Background Endophytic diazotrophic bacteria colonize several non-leguminous plants and promote plant growth. Different mechanisms are involved in bacteria-induced plant growth promotion, including biological nitrogen fixation (BNF), mineral solubilization, production of phytohormones, and pathogen biocontrol. Herbaspirillum seropedicae is a broad-host-range endophyte that colonizes sugarcane, rice, wheat, sorghum, and maize, and has been used as a biofertilizer. Contrasting results between greenhouse and field experiments have prompted efforts to improve the consistency of the plant response to microbial stimulation. Aims The aim of this study was to evaluate the effect of the presence of humic substances on inoculation of maize (Zea mays L.) with H. seropedicae. Methods Two experiments were conducted: one in the greenhouse using sand and nutrient solution and the other a field trial in soil with low natural fertility and to which was applied N in the form of urea (50 kg ha−1). In the greenhouse, pre-emerging seeds were inoculated with a solution of H. seropedicae (109 cells mL−1) in the presence of humic substances isolated from vermicompost (10, 20, or 30 mg C L−1); in the field trial, bacteria combined with humate were added as a foliar spray (450 L ha−1). Results At early stages (7 and 45 days old) in the greenhouse, the treatment activated plant metabolism including enhancement of plasma membrane H+-ATPase activity, alteration of sugar and N metabolism, and greater net photosynthesis. The number of viable bacterial cells was higher in root tissues when inoculation was in the presence of soluble humic substances. Foliar application of endophytic diazotrophic bacteria and humic substances increased maize grain production 65 % under field conditions. These results show a promising use of humic substances to improve the benefit of endophytic diazotrophic inoculation.
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Humic acids crossinteractions with root and organic acids
Article
Full-text available
The apparent high molecular mass of humic acids (HAs) hardly seems compatible with their direct effects in plant physiology. However, previous evidence has indicated that HAs are non-covalent associations of relatively small molecules, which can be broken down by the action of organic acids. The aim of this work was to evaluate the effects of organic acids on the structure of HAs by spectroscopy and on their bioactivity by following the responses of maize root growth. Changes in the exudation of organic acids from maize seedlings treated with HAs at 50 mg C L−1 were evaluated by high-performance liquid chromatography. The results are in agreement with the concept that HAs are chemical aggregates that acquire characteristics typical of low-molecular-mass humic substances when exposed to organic acids exuded by the roots. Maize seedlings grown in solutions supplemented with HAs plus citric acid at 0.0005, 0.005 and 0.05 mM exhibited significant changes in their root area, primary root length, number of lateral roots and lateral root density and increases in plasma membrane H+-ATPase activity. Furthermore, the root exudation profile of plants treated with HAs exhibited an increase in the efflux of oxalic and citric acids, with a concurrent decrease in malic and succinic acids. These data reveal a crosstalk between HAs and plants where the exudation of organic acids from the roots influences and is influenced by bioactive molecules released from HAs during root development.
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Agronomic and environmental aspects of phosphate fertilizers varying in source and solubility: An update review
Article
Full-text available
  • Mar 2011
This review discusses and summarizes the latest reports regarding the agronomic utilization and potential environmental effects of different types of phosphate (P) fertilizers that vary in solubility. The agronomic effectiveness of P fertilizer can be influenced by the following factors: (1) water and citrate solubility; (2) chemical composition of solid water-soluble P (WSP) fertilizers; (3) fluid and solid forms of WSP fertilizers; and (4) chemical reactions of P fertilizers in soils. Non-conventional P fertilizers are compared with WSP fertilizers in terms of P use efficiency in crop production. Non-conventional P fertilizers include directly applied phosphate rock (PR), partially acidulated PR (PAPR), and compacted mixtures of PR and WSP. The potential impacts of the use of P fertilizers from both conventional (fully acidulated) and non-conventional sources are discussed in terms of (1) contamination of soils and plants with toxic heavy metals, such as cadmium (Cd), and (2) the contribution of P runoff to eutrophication. Best practices of integrated nutrient management should be implemented when applying P fertilizers to different cropping systems. The ideal management system will use appropriate sources, application rates, timing, and placement in consideration of soil properties. The goal of P fertilizer use should be to optimize crop production without causing environmental problems. KeywordsPhosphate fertilizers–Agronomic effectiveness–Cadmium–P runoff–Eutrophication
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Factors determining rock phosphate solubilization by microorganism isolated from soil world
Article
  • Nov 1996
Forty two soil isolates (31 bacteria and 11 fungi) were studied for their ability to solubilize rock phosphate and calcium phosphate in culture medium. Eight bacteria and 8 fungi possessed solubilizing ability. Pseudomonas cepacia and Penicillium purpurogenum showed the highest activity. There was a correlation between final pH value and titratable acidity (r=-0.29 to -0.87) and between titratable acidity and soluble phosphate (r=0.22 to 0.99). Correlation values were functions of insoluble phosphate and of the group of microorganisms considered. A high correlation was observed between final pH and soluble phosphate only for the rock phosphates inoculated with the highest concentration of solubilizing bacteria (r=-0.73 to -0.98).
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