Kasper Jacob Steensgaard Jensen’s research while affiliated with IT University of Copenhagen and other places

Prolonged waterlogging in agricultural fields has severe consequences for the crop development and growth, and could potentially lead to higher N losses. In this study, a 3.93 ha agricultural field in Denmark was separated into two parts of well-drained (WD) and poorly-drained (PD) based on the installation depth of the tile drains. The field was continuously monitored for drainage, soil water dynamics, nitrogen leaching through the drains, and grain dry matter and nitrogen yields in a 4-year period (2017–2020). Furthermore, denitrification potential of the top 1 m of the soil at both parts of the field was measured through the denitrifying enzyme activity assay, and a 1D Daisy model was utilized to capture the differences between water and nitrogen balances at WD and PD. Results indicated that on average over the 4 years, annual harvested nitrogen in the crops at PD was 14% lower compared to WD, with a significant reduction of 33% in 2017–2018, that coincided with the longest period of waterlogging at PD. Moreover, greater losses of nitrogen through leaching from drainage and other pathways were measured at the PD (109 kg N ha⁻¹ ya⁻¹) compared to the WD (95 kg N ha⁻¹ ya⁻¹). Based on the simulations, losses through preferential flow pathways to the drains dominated at PD and most of the denitrification is expected to occur within the topsoil. Future studies could significantly benefit from monitoring the redox dynamics in the top 30 cm of the PD soils, and increasing the depth of tiles drains by redrainage could reduce the N losses of poorly drained agricultural soils.

The benefits of drainage with respect to improving yield level and stability was recognized millennia ago, hence drainage is an old agronomical practice. However, agriculture is under constant change, and few long-term field studies exploring the need for drainage have been conducted in modern north European agricultural systems. The objective of this study is to describe yield variations in modern cereal crops as a function of the different dynamic drainage conditions that may appear in ordinary agricultural fields with old drainage systems, to this end seven years of field experiments were conducted at up to 3 field locations per year and with different N application levels. Drainage conditions were quantified annually in an index (SEW60) accumulating on a daily basis the depth of shallow groundwater (< 60 cm beneath the soil surface). Yield reductions up to 25 % was caused by poor drainage, despite that no visual plant symptoms were observed during the growing season. The yield variation across years, crops, and locations could be explained by SEW60. Yield effects of poor drainage were not significantly different for the investigated N-fertilization levels.This indicates that other factors than N are important for reduction of the yield potential induced by poor field drainage. The results clearly show the importance of good drainage as basis for agriculture in a region with excess precipitation, and they emphasize the need to focus on drainage conditions in a changing climate with increasing winter precipitation. Additionally, this can be a considerable factor in future water management trying to reconcile environmental and agricultural needs.

Artificial drainage is an essential water management system in agriculture and tile drains are implemented on more than half of the agricultural fields in Denmark. Water that flows through the drainpipes to surface water bodies can transport contaminants. Quantifying the drainage discharge is an important step towards understanding the flow dynamics on the field. The objective of this study was to predict the tile drainage discharge based on meteorological data and the groundwater level with the means of machine-learning algorithms.