Subsurface agricultural drainage has benefited crop production for millennia, but it was not until the mid-1800s when invention of the pipe extruder led to mass installation of drainage networks. Now, 130-200 Mha of the world’s most productive cropland – including northwestern Europe and the U.S. Corn Belt – benefit from agricultural drainage. Without the ability to drain and transport excess water, large portions of these regions would not support crops.
Climate change and agricultural intensification are increasing the amount and intensity of drainage. An additional 450 Mha of undrained cropland might benefit from drainage . How we expand and intensify drainage systems will impact a range of ecosystem services including nitrogen use efficiency, soil carbon sequestration, greenhouse gas emissions, water quality and food production.
Here in the Midwest U.S., we are at the center of one of the most intensively drained agricultural landscapes on Earth. We know drainage is critical for economical crop production. We also know it creates large downstream nutrient losses. The largest water provider in the state of Iowa is home to the largest nitrate removal facility in the world. Where does our nitrate runoff end up? The Gulf of Mexico, home to one of the largest hypoxic zones in the world.
One fall, I was scheduling a meeting with a farmer. I thought late October, immediately after harvest would be a good time to visit. He replied: “Mike, I have no time between harvest and freeze because I install drainage non-stop”. At that moment, I began to appreciate the practical importance of drainage – and the opportunity to better design drainage systems for both the farmer and the environment.
At the same time, collaborations with crop physiologists and ecosystem modelers were revealing strong relationships between depth to water table, root biomass and optimum nitrogen fertilizer rates [2,3].
We began to consider: How can drainage increase nitrate loss, while improving crop yield and fertilizer nitrogen use efficiency? As we pieced together the effects of drainage on the nitrogen cycle, we collaborated with a drainage engineer to develop and test hypotheses that matched our scientific understanding of the system and account for the realities drainage engineering. Our results pointed to a number of opportunities to sustainably intensify drainage systems by altering drain depth and spacing while incorporating edge-of-field conservation practices such as wetlands.
Our paper, ‘Sustainable intensification of agricultural drainage’ https://www.nature.com/articles/s41893-019-0393-0  points to a number of opportunities to sustainably intensify drainage systems by altering drain depth and spacing while incorporating edge of field conservation practices such as denitrification wetlands. These alternative drainage system designs can mitigate and adapt to climate change while increasing crop production and environmental performance.
One unique aspect of drainage networks is that they are managed by a patchwork of highly organized quasi-municipal organizations that have the power to assess fees. Individual farmers pay to maintain ‘field’ drains at their own will, but share the costs to maintain and upgrade larger drainage ‘mains’ that benefit all farmers in the network. This structure offers great opportunities to link policies and science that ultimately create solutions for the sustainable intensification of agriculture.
1. Smedema, L. K., Vlotman, W. F. & Rycroft, D. W. Modern Land Drainage. (Taylor & Francis, 2004).
2. Ordóñez, R. A. et al. Maize and soybean root front velocity and maximum depth in Iowa, USA. F. Crop. Res. 215, 122–131 (2018).
3. Poffenbarger, H. J. et al. Maximum soil organic carbon storage in Midwest U.S. cropping systems when crops are optimally nitrogen-fertilized. PLoS One 12, (2017).
4. Castellano, M. J., Archontoulis, S. V., Helmers, M. J., Poffenbarger, H. J. & Six, J. Sustainable Intensification of Agricultural Drainage. Nat. Sustain. 2, 914–921 (2019).