INCREASING THE SOIL-TEMPERATURE TO STUDY GLOBAL WARMING EFFECTS ON THE SOIL-NITROGEN CYCLE IN AGROECOSYSTEMS

According to the GCMs air temperature will increase 3-5 degrees C abov e ambient in Central Europe. As one consequence the element turnover i n terrestrial ecosystems should change; in particular, the large soil carbon and nitrogen pools are crucial because of their potential to fu rther 'pollute' the globe with liquid and gaseous compounds. According to the goals of the International Geosphere-Biosphere Programme (IGBP ) an ecosystem manipulation was carried out to increase the temperatur e of the top soil in an agroecosystem 3 degrees C above ambient and to study the effects on the nitrogen cycle. The experimental design, cal led HOTWORM, could be proved during a 3-month winter period to keep a constant temperature difference of 3 degrees C above ambient including freezing-thawing cycles. No changes in the soluble nitrogen pools cou ld be measured at the end of the investigation, probably because of th e shea heating period and the high spatial variability. However, N2O-N emissions were much higher in the unheated plot (0.233 kg ha(-1)) com pared with the heated one (0.058 kg ha(-1)). This effect could be caus ed by more frequent freezing-thawing cycles in the unheated plots, whi ch showed the highest emission rates. The importance of the reduced wa ter content in the heated plot could not be evaluated in this investig ation. Based on the experiences of this study a schedule for intensifi ed field experiments was developed.