BENEATH THE SURFACE: SUBSURFACE DRAINAGE AND THE MICROBIOME
Here at Miner Institute, we’re beginning to wrap up the harvesting season, and that brings yield variability into focus. During this time, you notice parts of the field where plants were smaller than the rest. Currently, one of our smaller corn fields is occupied by a study focused on microbial activity with plots separated into a grid pattern. During analysis we noticed that there was a gradual increase in size as we went from the start of each plot to the back, which is an unusual pattern for growth. I later discovered that this field had tile drainage runs perpendicular to the rows of corn rather than parallel like most fields at Institute farm, which could be an explanation for the difference in growth. Subsurface drainage is a common strategy on farms to help remove excess water from poorly drained fields during the wet season and prevent flooding while crops are growing. Improvements like this can increase field trafficability which allows for more timely planting, fertilization and harvesting because tractors aren’t getting stuck in waterlogged soil or ruining the soil structure (Moore, 2016). Many farmers know the benefits of using tile drainage, but few understand how important it can be for the soil microbiome.
Corn is a high yielding crop and needs to meet high nutrient demands to reach its full potential. Due to its large demand for nutrients, like nitrogen, corn relies heavily on interactions with soil microbes, making tile drainage a useful tool for encouraging microbial activity. Many of the microbes that are beneficial to plant growth are aerobic, meaning they require oxygen to survive and grow. Gas exchange occurs from the atmosphere through pores in the soil, but excess water can fill pores in the soil. Since oxygen doesn’t diffuse easily into water, less oxygen is able to reach the plant’s roots and microbiome. With subsurface drainage, the water table is much lower, meaning oxygen levels in the soil are increased, stimulating microbial activity and allowing the plant oxygen necessary for growth. Increased microbial activity can lead to an acceleration in organic matter turnover (decomposition) and mineralization, increasing the amount of nutrients available to the plant during the growing process (Ma et al., 2025).
Saturated fields can have the opposite effect on the microbial community, creating conditions that benefit anerobic microbial activity. Instead of using oxygen during respiration, anaerobic microbes use other ions including elements like sulfate, iron, and nitrate. Microbial processes can also change the chemical forms and availability of these nutrients. For example, the denitrification process, which is promoted by oxygen-limited conditions, allows some microbes to convert available versions of nitrate into gaseous forms of nitrogen which cannot be taken up by the plant (Bayer, 2026). Flooded conditions can also facilitate microbial growth, such as pathogens causing disease to spread in the plot. A lack of oxygen available to the roots can cause plant stress, increasing its vulnerability to diseases. Water molds, such as pythium, are microbes that thrive in oversaturated soils as they use water pooled in the field to transport the disease from one plant to another (Coulter et al., 2021).
As the growing season comes to an end, it’s important that we not only focus on the yield but also consider what might be happening beneath the surface because it's more important than some people think. Subsurface drainage is a technique that allows adequate soil moisture without suffocating the plant's roots or the microbial community. If your field already has subsurface drainage, it could be helpful to look at your field’s yield map and identify low yielding areas which helps pinpoint where extra drainage may be helpful. It’s also worth noting that subsurface drainage doesn’t stop at installation since regular and continuous maintenance is required to ensure proper function of the system. During the offseason, tasks such as clearing debris from the outlet or checking the field for signs of soil erosion require little effort and can have a big return next season (Curell, 2012). For example, last year, unexpected drainage issues occurred in one of our fields. We later discovered that a beaver had been building a dam on our outlet drain.
— Luke Trombley
