The interest in drainage and disposal of surplus precipitation as an essential part of agriculture goes back to the beginning of civilisation. Many regions not least in Northern Europe experience an increase in surplus precipitation with more extremely wet periods, and this trend is expected to continue according to climate scenarios.This challenges the capability of the old drainage systems (tiles and stream s) to maintain drainage conditions at the level required to support production on large agricultural areas. The adverse effects of waterlogging have been demonstrated in numerous trials. However, the majority of newer trials are conducted as lysimeter or greenhouse setups focusing on process description. The reported drainage field trials are mostly with constant or unquantified water levels over few growing seasons. This complicates the quantitative interpretation of the yield response considering the implications of climate, crop management and soil type. The interaction between these factors can be substantial and encourage the examination of the drainage response under drainage conditions representative for artificially drained agricultural fields in Denmark. Considering the large proportion of tile drained areas in the temperate humid climate of Northern Europe, there are few field studies to support the implication of drainage on agricultural production and environmental impact under modern agricultural conditions. For this reason, multilocational trials were conducted over several years in fields with old drainage systems. Yield response to drainage conditions and its variation were quantified. Drainage conditions were characterized on the basis of continuous measurements of water table depths. These measurements were each year transformed into a single drainage index, which was used as the explanatory variable for the grain- and N-yield. Significant yield reductions of 25% in winter wheat and spring barley were found due to poor drainage conditions representing common field conditions found in Denmark and without visually observed symptoms during the growing season. The yield results from 11 site years were strongly correlated to the SEW60 drainage index for both dry matter and N yield. The treatment of three N levels applied did not interact with drainage but was an additive factor, indicating limited possibilities to compensate yield depressions by application of extra N fertilisation. Soil surface temperature is a fundamental physical variable influenced by drainage. Low temperatures in the spring can reduce plant growth and thus the yield potential. Therefore, soil temperature was measured and modelled at field scale by simulations on the basis of soil texture, groundwater and weather data. Both measurements and modelling showed that the average dailymaximum soil surface temperature was approximately 1OC higher in the spring months (March, April and May) on well drained plots compared to the poorly drained plots. The modelling showed higher soil heat flux during the daytime derived from less energy used on evapotranspiration under well drained conditions. The detailed level of process description in the modelling of the system in this scale can serve as basis for further investigations of drainage process description. This enable us to generalise effects on basis of soil properties, water measurements in the system and weather. There are limitations to the interpretation of the results regarding the specific crop management, weather and soil and interaction in between these factors. The clearly observed yield response to drainage conditions as specified in a drainage index quantifies the significant impact on production and nitrogen use efficiency in a modern agricultural system under humid temperate conditions and is believed to have the potential to be a contribution in future water management decisions