Carbon balance of a rain-fed maize field

摘要

This thesis analyses micrometeorological measurementsudcarried out from June 2004 until Octoberud2006 in the framework of the INTERREG IIIaudProject Nr. 3c.10 ”Impacts of climate change on vegetationudin the Upper Rhine Valley”.udThe study addresses the exchange processes ofudcarbon, water and energy of a rain-fed field underudmaize-fallow rotation. Measurements with anudultrasonic anemometer-thermometer, an open-pathudCO2/H2O infra-red gas analyser and of the meteorologicaluddrivers such as photosynthetic photon fluxuddensity (PPFD), temperature and precipitation giveudinsight in the interaction between atmosphere, soiludand vegetation.udEnergy balance considerations show similar patternsudof the energy flux densities for vegetation periodsudand bare field conditions. Energy balance closure isud80 % and 52 %, respectively. A closer look shows audclear diurnal pattern with bad closure during nighttimeudand an increasing closure fraction during daytime,udin fact resulting in an overshooting in late afternoon.udEvapotranspiration shows a clear seasonal patternudwith maximum values of ~3.5 mm d-1 reached inudmid-July. The total water need for the three subsequentudyears is 321, 397, and 422 mm per kg kernelsud(yield). The water use efficiency shows a strong relationshipudwith PPFD and the amount of biomass.udThe focus of the study is on carbon balance. Duringudthe three subsequent vegetation periods 930, 785,udand 841 g C m-2 are sequestered, respectively. Theudyield is 455, 417, and 340 g C m-2. About 40 %udof the biomass remaining on the field at harvest areuddecomposed during the dormant season. The resultingudnumbers for the carbon balance show a ”yearly”udsink of this agroecosystem of ~250 g C m-2. Besidesudunlimited photosynthetic active radiation theudcombination of the optimal temperature range withudthe needed precipitation amount corresponding toudthe need of the actual growth stage are essential forudoptimal maize growth.