Urine patches in pastures rank among the highest sources of the greenhouse gas nitrous oxide (N 2 O) from animal production systems. Previous laboratory studies indicate that N 2 O emissions for urine-N in pastures may increase with a factor five or eight in combination with soil compaction and dung, respectively. These combinations of urine, compaction and dung occur regularly in pastures, especially in socalled camping areas. The aims of this study were (i) to experimentally quantify the effect of compaction and dung on emission factors of N 2 O from urine patches under field conditions; (ii) to detect any seasonal changes in emission from urine patches; and (iii) to quantify possible effects of urine concentration and -volume. A series of experiments on the effects of compaction, dung, urine-N concentration and urine volume was set up at a pasture on a sandy soil (typic Endoaquoll) in Wageningen, the Netherlands. Artificial urine was applied 8 times in the period August 2000-November 2001, and N 2 O emissions were monitored for a minimum of 1 month after each application. The average emission factor for urine-only treatments was 1.55%. Over the whole period, only soil compaction had a clear significant effect, raising the average N 2 O emissions from urine patches from 1.30% to 2.92% of the applied N. Dung had no consistent effect; although it increased the average emissions from 1.60% to 2.82%, this was clearly significant (P < 0.01) for only one application date and marginally significant (P ¼ 0.054) for the whole experiment. Both compaction and dung increased water-filled pore space (WFPS) of the topsoil for a more prolonged time than high urine volumes. No effect of amount of urine-N or urine volume on N 2 O emissions relative to added N was detected for the whole experiment. There were clear differences between application dates, with highest emissions for urine-only treatments of 4.25% in October, 2000, and lowest of )0.11% in June, 2001. Emissions peaked at 60-70% WFPS, and decreased rapidly with both higher and lower WFPS. We conclude that compaction leads to a considerable increase in the N 2 O emissions under field conditions, mainly through higher WFPS. Dung addition may have the same effect, although this was not consistent throughout our experiment. Seasonal variations seemed mainly driven by differences in WFPS. Based on this study, mitigation strategies should focus on minimizing the grazing period with wet conditions leading to WFPS > 50%, avoiding camping areas in pastures, and on avoiding grazing under moist soil conditions. Greenhouse gas budgets for grazing conditions should include the effects of soil compaction and dung to represent actual emissions.

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In this paper, we analyze the methods that are used in The Netherlands to upscale in-situ groundwater measurements in time and in space, and how the selected combinations of upscaling methods affect the resulting groundwater characteristic. In The Netherlands, a three-step approach is used to obtain groundwater characteristics for a specific area: (1) in-situ monitoring of the water table depth; (2) temporal upscaling; and (3) spatial interpolation and aggregation. The three-step approach is, however, not standardized, but a combination of the following methods is used: (i) four methods to measure/monitor the phreatic water table; (ii) four methods for temporal aggregation; and (iii) four methods for spatial interpolation and/or aggregation. Over the past sixty years, several combinations of these methods have been used. Our review shows that the use of these different combinations in the approach to measure and interpret water table depths has resulted in significant systematic differences in the corresponding groundwater characteristics and that there are many sources of potential error. Error in the in-situ measurement of the water table depth can be as high as 1 meter. Errors in the temporal aggregation are in the range of 10 to 20 cm and for the spatial interpolation between 20 to 50 cm. We show that there has been no systematic assessment of how these errors influence the resulting groundwater characterization. Thus, we cannot answer the question of whether drought stress in The Netherlands is under-or overestimated. Based on these findings we give recommendations for a systematic approach to groundwater characterizations studies that can minimize the impact of errors.

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