?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=https%3A%2F%2Forgprints.org%2Fid%2Feprint%2F4053%2F&rft.title=Density+and+relative+frequency+effects+on+competitive+interactions+and+resource+use+in+pea-barley+intercrops&rft.creator=Hauggaard-Nielsen%2C+Henrik&rft.creator=Andersen%2C+Mette+Klindt&rft.creator=Joernsgaard%2C+Bjarne&rft.creator=Jensen%2C+Erik+Steen&rft.subject=+Crop+combinations+and+interactions&rft.description=Intercropping+advantages+may+be+influenced+by+both+plant+density+and+relative+frequency+of+the+intercrop+components.+In+a+field+study+barley+(Hordeum+vulgare+L.)+and+pea+(Pisum+sativum+L.)+were+sole+cropped+and+intercropped+at+three+densities%2C+corresponding+to+i)+half+of+the+recommended%2C+ii)+the+recommended+and+iii)+twice+the+recommended+plant+density.+Two+intercrops+combinations+were+included+holding+1%2F3pea%2B2%2F3barley+and+2%2F3pea%2B1%2F3barley+relative+to+the+sole+crop+densities+employed.+%0D%0AFor+three+growth+intervals+within+the+whole+growing+period%2C+the+relative+performance+and+interactions+between+the+two+crops+were+assessed+using+the+Relative+Efficiency+Index+(REIc).+The+relative+performance+of+the+two+species+varied+over+the+growing+season+and+was+influenced+by+plant+density+and+relative+frequency+of+pea+and+barley.+Barley+came+off+to+a+better+start+whereas+pea+was+in+general+more+growth+efficient+once+the+initial+growth+phases+had+been+passed.+This+reversal+in+relative+growth+efficiency+along+with+the+observation+that+early+barley+dominance+did+not+appear+to+suppress+pea+growth+indicates+that+differences+in+phenology+played+a+role+in+shaping+the+prevailing+dynamics.+%0D%0AWhereas+increasing+plant+density+had+a+clear+positive+effect+on+the+growth+of+pea%2C+the+growth+of+the+initially+stronger+barley+component+of+the+intercrops+responded+quite+differently.+From+being+unaffected+by+changes+in+density+at+the+middle+of+the+growth+season+the+effects+of+increasing+plant+density+became+severe+at+the+end+of+the+growing+period%2C+biomass+yields+falling+with+increased+plant+density.+Calculations+of+the+competitive+ratio+of+barley+relative+to+pea+(CRBP)+for+the+growth+season+as+a+whole%2C+showed+that+barley+was+most+competitive+at+low+and+recommended+plant+density+(CRBP%3E1)+whereas+at+high+density+the+pea+crop+became+the+competitively+superior+component+of+the+intercrops+(CRBP%3C1).+Changes+in+the+relative+frequency+of+barley+in+the+intercrops+affected+its+competitive+impact+on+pea%2C+competitive+strength+increasing+with+decreasing+relative+frequency+of+barley.%0D%0AUsing+the+Land+Equivalent+Ratio+(LER)+as+a+measure+of+resource+complementarity+we+found+that+the+LER+ratios+calculated+on+the+basis+of+final+biomass+yields+(from+0.9+to+1.2)%2C+expressed+resource+complementarity+in+almost+all+studied+intercrops.+However+the+degree+of+resource+complementarity+attained+was+not+directly+affected+by+changes+in+plant+density+or+relative+frequency.%0D%0AWhen+intercropping+pea+with+barely+at+low+and+recommended+density+the+pea+increased+its+reliance+on+atmospheric+nitrogen+fixation+compared+to+the+pea+sole+crop%2C+throughout+the+growth+period%2C+implying+that+the+barley+crop+competed+strongly+for+soil+nitrogen.+At+high+plant+density+barley+crop+growth+was+clearly+suppressed+by+the+end+of+the+growing+period+and+was+thereby+unable+to+push+intercropped+pea+to+increase+nitrogen+fixation.+With+respect+to+soil+nitrogen+uptake+there+were+no+effect+of+plant+density+but+a+strong+effect+of+the+relative+frequency+of+pea+in+the+intercrop%2C+the+greater+the+proportion+the+lower+the+uptake.%0D%0AChanges+in+the+competitive+strength+of+the+pea+and+barley+crop+over+the+growing+season+had+a+marked+effect+on+the+proportion+of+pea+in+the+final+grain+yields+of+the+intercrops.+At+low+and+recommended+density+the+proportions+of+pea+and+barley+in+the+final+grain+yield+was+not+markedly+different+from+the+expected+1%2F3pea%3A2%2F3barley+and+2%2F3pea%3A1%2F3barley+proportions+sown%2C+however+at+high+density+the+suppression+of+barley+strongly+increased+the+proportion+of+pea+in+the+final+grain+yield.+%0D%0AWith+the+exception+of+the+barley+sole+crop+weed%2C+infestation+levels+decreased+as+density+was+raised%2C+the+suppressing+effect+of+density+was+clearly+stronger+the+greater+the+frequency+of+pea+in+the+crop.+Early+germination%2C+rapid+initial+growth+and+tillering+ability+are+seen+as+likely+explanations+of+the+greater+competitive+strength+of+barley+towards+weeds.%0D%0AFrom+the+present+study+we+conclude+that+the+added+value+of+including+sequential+harvest+when+studying+interspecies+dynamics+was+well+worthwhile%2C+giving+valuable+information+on+interspecies+dynamics+that+would+have+been+hidden+had+we+chosen+to+evaluate+the+outcome+of+the+study+on+the+basis+of+data+from+one+final+harvest.+We+found+that+the+relative+performance+of+the+pea+and+barley+crops+varied+over+time+and+were+clearly+affected+by+changes+in+plant+density+and+relative+frequency.+This+points+at+the+potential+of+employing+density+and+relative+crop+frequency+as+%E2%80%9Cregulators%E2%80%9D+when+specific+intercrop+objectives+such+as+increased+competitiveness+towards+weeds+or+specific+grain+yield+composition+are+wanted.+%0D%0A&rft.publisher=Elsevier&rft.date=2005&rft.type=Journal+paper&rft.type=NonPeerReviewed&rft.format=application%2Fpdf&rft.language=en&rft.identifier=%2Fid%2Feprint%2F4053%2F1%2F4053.pdf&rft.identifier=+++Hauggaard-Nielsen%2C+Henrik%3B+Andersen%2C+Mette+Klindt%3B+Joernsgaard%2C+Bjarne+and+Jensen%2C+Erik+Steen+++(2005)+Density+and+relative+frequency+effects+on+competitive+interactions+and+resource+use+in+pea-barley+intercrops.+++Field+Crops+Research%2C+95+(2-3)%2C+pp.+256-267.++++++++