?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.title=Modelling+P+Dynamics+in+soil+-+Decomposition+and+Sorption%3A+Concepts+and+User+Manual&rft.creator=Gjettermann%2C+Birgitte&rft.subject=History+of+organics&rft.description=Weather-driven+simulation+modelling+has+become+an+important+component+of+studies+of+soil+nu-trients%2C+both+for+crop+growth+and+for+losses+by+leaching+to+the+environment.+In+order+to+model+phosphorus+(P)+dynamics+in+soil%2C+the+mobilisation+and+immobilisation+processes+of+inorganic+and+organic+P+species+is+important+for+quantifying+P+leaching+from+the+unsaturated+zone.+The+mobilization+and+immobilisation+processes+of+P+are+represented+in+this+project+by+sorption+and+desorption+of+P+and+by+decomposition+of+organic+matter+with+mineralization+and+immobilisation+of+P.+%0D%0AThe+code%2Fmodel+presented+here%2C+referred+to+as+the+P-Model%2C+works+with+another+model%2C+called+Daisy.+The+Daisy+code+delivers+input+data+of+water+content%2C+water+flux%2C+temperature%2C+inorganic+nitrogen+(N)%2C+crop+uptake+of+N%2C+and+crop+root+exudates%2C+to+the+P-Model.+The+P-Model+must+be+considered+as+a+prototype+of+a+P+module+in+Daisy%2C+as+the+user-friendliness+is+limited+and+not+all+aspects+are+described+in+details.+For+instance+crops+are+described+as+very+simple+sink+terms%2C+in+spite+of+the+fact+that+they+are+very+important+in+the+P+dynamic+of+soils.+Soil+ploughing+and+harrowing+are+not+included+in+the+P-Model+and+therefore+some+limitations+of+the+Daisy+set+up+must+be+considered.+%0D%0AThe+concept+of+the+turnover+of+soil+organic+matter+is+based+on+the+organic+matter+module+in+Daisy.+The+simulation+of+the+organic+matter+balance+and+the+nitrogen+dynamics+is+strongly+inter-connected+in+Daisy+as+the+organic+matter+model+is+considered+an+integral+part+of+the+overall+ni-trogen+balance+model.+It+is+assumed+that+the+activity+of+soil+microbial+biomass+is+related+to+the+substrate+availability%3B+and+that+it+is+reasonable+to+relate+the+N+mineralization+and+immobilization+with+decomposition+of+soil+organic+matter+(SOM).+Daisy+does+not+include+P+in+the+organic+matter+module.+However%2C+like+N+it+seems+reasonable+to+relate+P+mineralization+and+immobilization+to+the+decomposition+of+SOM.+%0D%0AIn+the+P-Model+organic+matter+is+defined+with+respect+to+C%2C+N%2C+and+P+and+is+represented+by+different+pools+in+the+model%2C+representing+easily+degradable+and+recalcitrant+pools%2C+microbial+pools%2C+and+a+dissolved+pool.+The+dissolved+organic+matter+(DOM)+pool+is+produced+by+microbial+degradation+of+organic+matter+and+by+physical%2Fchemical+desorption+from+the+most+bio+available+pool+of+soil+organic+matter.+Hence%2C+DOM+may+also+be+immobilized+by+sorption+to+the+soil+organic+matter+pool.+The+P-model+also+includes+addition+of+organic+and+inorganic+fertilizers%2C+crops%2C+and+solute+transport+by+convection.+%0D%0AOne+of+the+main+issues+during+parameterisation+of+the+DOM+dynamics+has+been+to+identify+and+particularly+to+quantify+the+sources+of+DOM+in+soil.+It+is+assumed+that+DOM+is+produced+by+the+soil+microbial+biomass+(SMB)+pool+and+the+SOM+pool.+DOM+production+is+not+directly+linked+to+the+input+of+organic+material+as+fresh+litter%2C+dead+roots%2C+and+organic+fertilizer%2C+because+the+contri-bution+of+DOM+from+all+these+different+sources+probably+is+very+different+and+not+known+at+this+stage.+However%2C+theses+sources+is+very+bioavailable+to+the+microbial+biomass+promoting+fast+turnover+and+growing+microbial+biomass%2C+which+contribute+to+the+production+of+DOM.+Hence%2C+the+DOM+dynamic+is+closely+linked+to+the+dynamic+of+the+AOM+pools.+The+biological+decomposition+of+DOM+and+associated+P+in+the+P-Model+has+been+parameterised+from+literature+(e.g.+C%2FP+ratios%2C+decay+rates+and+diffusion+coefficients+of+DOM).+%0D%0AThe+P-Model+considers+sorption+and+desorption+of+DOM+in+soil%2C+by+assuming+that+dissolved+organic+P+(DOP)+and+dissolved+organic+N+(DON)+follows+dissolved+organic+C+(DOC)+sorp-tion%2Fdesorption+in+soil.+When+DOM+is+sorbed+it+is+assumed+to+be+associated+to+a+part+of+the+SOM+pool.+Sorption%2Fdesorption+of+DOC+takes+advantages+of+estimated+relationships+linking+soil+properties+to+sorption+properties+across+a+range+of+soil+types.+The+Initial+Mass+approach+is+used+to+estimate+a+DOC+concentration+specific+for+the+soil%2C+where+no+net+sorption%2Fdesorption+of+DOM+occurs.+The+sorption%2Fdesorption+dynamics+of+DOM+and+associated+P+in+the+P-Model+have+been+parameterised+from+sorption+data+and+field+experiments.+An+empirical%2C+kinetic+term+couples+the+%C3%A2%C2%80%C2%98equilibrium%C3%A2%C2%80%C2%99+concentration+to+the+actual+DOM+concentration+in+the+soil%2C+incorporating+considera-tions+as+diffusion+and+sorption+time+into+the+description+of+the+sorption%2Fdesorption+process.+De-pending+on+whether+the+DOM+concentration+is+above+or+below+the+%C3%A2%C2%80%C2%98equilibrium%C3%A2%C2%80%C2%99+concentration+then+the+DOC+concentration+in+the+soil+is+reduced+or+increased%2C+respectively.+Reducing+the+sorp-tion%2Fdesorption+rate+coefficients+the+exchange+between+part+of+the+SOM+pool+and+the+DOM+pool+is+reduced.+The+best+fit+of+simulations+to+measured+DOC+and+DOP+concentrations+in+batch+ex-periments+was+found+by+using+desorption+and+sorption+rate+coefficients+of+0.001+hour-1.+%0D%0AAdditionally%2C+the+P-Model+considers+sorption+of+inorganic+P%2C+which+is+described+by+a+three-step+mechanism%3A+1)+A+fast+sorption+mechanism%2C+and%2C+2)+a+relative+slow+absorption+mechanism%2C+plus+3)+a+very+slow+fixation+process.+Thus%2C+its+is+hypothesised+that+inorganic+phosphate+first+binds+to+easily+available+sorption+sites+with+high+affinity%2C+and+then+the+less+available+sites+which+is+limited+by+diffusion+and+further+migration+into+the+soil+particle+to+sorption+sites+less+available.+Langmuir+describes+all+three+processes+at+%C3%A2%C2%80%C2%98equilibrium%C3%A2%C2%80%C2%99.+As+for+DOM%2C+kinetic+terms+couples+the+%C3%A2%C2%80%C2%98equilibrium%C3%A2%C2%80%C2%99+concentrations+of+the+different+inorganic+P+pools+to+the+actual+P+concentration+in+the+soil%2C+incorporating+considerations+as+diffusion+and+sorption+time+into+the+description+of+the+sorption%2Fdesorption+processes.+The+sorption+of+inorganic+P+has+been+parameterised+from+sorption+data+and+literature+(e.g.+sorption+affinity+constant+and+sorption+capacities).+Due+to+the+concept+of+instantaneous+process+of+adsorption%2C+which+implies+an+adsorption+rate+coefficient+of+1+h-1+in+this+model%2C+the+other+rates+have+been+fitted+based+on+this+assumption.+The+process+of+absorption+has+been+fitted+to+obtain+equilibrium+within+3-4+days.+The+fixation+process+has+been+adjusted+not+obtain+equilibrium+during+14+days.+The+slow+desorption+rate+has+not+been+included+during+these+test.+So%2C+whether+the+slow+process+is+considered+reversible+or+irreversible+is+still+up+to+discussion+in+the+concept.+The+distribution+of+the+sorption+capacities+between+the+three+P+pools+was+shown+to+have+limited+effect+of+the+sorption+dynamic+The+distribution+of+the+total+sorption+capacity+between+the+three+sorbed+phases+has+been+parameterised+based+on+the+assumption+that+the+quickly+sorbed+fraction+has+1%2F3+of+total+sorption+capacity.+By+fitting+the+P-Model+to+data+of+sorption+experiments+on+two+different+soils%2C+it+was+found+that+1%2F4+of+the+total+sorption+capacity+is+allocated+to+the+absorbed+phase+for+both+top+and+subsoils.+The+rest+of+the+sorption+capacity+is+allocated+to+the+slow%2C+fixed+pool.+The+sorption+affinities+are+very+dominating+for+the+sorption+dynamic.+The+sorption+affinities+were+initially+assumed+to+be+in+the+range+of+10-120+mM-1+as+of-ten+found+by+fitting+Langmuir+constants+during+sorption+experiments.+However%2C+the+best+fit+to+measured+sorption+data+to+two+subsoils+were+made+by+using+rather+high+values+for+the+sorption+affinity+constants+(400-200+mM-1)+for+the+adsorbed%2C+absorbed+and+fixed+processes.+The+P+sorp-tion+of+the+two+topsoils+behaves+very+different+which+could+be+due+to+a+pH+effect.+It+was+not+possible+to+parameterise+the+affinity+constants+for+the+three+sorption+processes+similar+for+the+two+top+soils%2C+maybe+because+effects+of+initial+soil+pH+are+not+taking+into+account+in+the+parameteri-sation.+%0D%0AOnly+part+of+the+P-Model+has+been+validated+on+field+data.+The+calculation+of+DOC+and+DON+mobilisation+%2F+immobilisation+is+validated+at+three+fields+with+different+soil+treatments+located+at+the+Burreh%C3%83%C2%B8jvej+field+at+Research+Center+Foulum+in+the+central+part+of+Jutland.+The+simulations+are+compared+with+measured+DOC%2C+DON%2C+NO3+and+NH4+concentrations+sampled+from+suctions+cups+installed+in+the+three+fields.+The+simulations+show+that+in+the+topsoil+the+DOM+is+mainly+produced+by+biological+SOM+turnover+during+summertime+and+chemical%2Fphysical+release+from+SOM+at+all+time.+The+yearly+fluctuation+of+DOM+concentration+is+related+to+the+microbial+activity.+High+fluctuations+of+DOM+which+are+related+to+microbial+activity+are+diminished+by+the+chemical%2Fphysical+sorption%2Fdesorption+processes+which+attempts+to+keep+the+DOC+concentration+steady+at+a+certain+level.+For+the+soil+treated+with+9+year+of+grass+clover%2C+the+higher+DOCand+DON+fluctuations+in+the+topsoil+are+slightly+diminished+in+the+simulations+in+relation+to+the+measured+DOC+and+DON+concentration.+For+the+two+other+soil+treatments+the+DOC+and+DON+concentration+show+less+fluctuations+and+are+simulated+better.+%0D%0A&rft.date=2004-12&rft.type=Report&rft.type=NonPeerReviewed&rft.format=application%2Fpdf&rft.identifier=http%3A%2F%2Forgprints.org%2F5388%2F1%2F5388.pdf&rft.identifier=Gjettermann%2C+Birgitte+(2004)+Modelling+P+Dynamics+in+soil+-+Decomposition+and+Sorption%3A+Concepts+and+User+Manual.&rft.relation=http%3A%2F%2Forgprints.org%2F5388%2F