Effects of drainage system renewal on nutrient leaching and crop yield

A clear strategy for adapting agricultural drainage to future climate change is important for environmental and economic reasons. In a project aiming to develop recommendations for primary/renewed drainage of clay soils, we are studying how drainage system renewal affects nutrient leaching and crop yield in a field experiment consisting of 12 individually drained plots allocated to four treatments with three replicates. Flow measurement and flow-proportional logger-controlled water sampling on runoff from each individual plot are carried out at a measuring station.The first year’s results show a clear effect of re-drainage on phosphorus and nitrogen loads in subsurface runoff. The highest total loads of nitrogen and lowest total loads of phosphorus were observed in treatments with 10 m drain spacing and lime incorporated in trench backfill. The lowest total nitrogen loads and highest total phosphorus were observed for an old tile drainage system with 10 m drain spacing. The environmental impact of re-drainage might thus be a tradeoff, as phosphorus loads may decrease with re-drainage of clay soils, while more intensive drainage poses a risk of increased nitrogen loads.Yield data from two experimental years indicate that investing in new drainage systems can be profitable for farmers, with crop yield being 3-20% higher for plots with new drainage systems compared with old tile drainage. More experimental years are needed to confirm the long-term effects of different types of drainage systems