Tile drainage is an important practice on farms in northern climates with short growing seasons where improved field trafficability can extend the growing season, significantly increase crop yields, and minimize soil compaction by field equipment (e.g., tire ruts). The extended growing season can also provide greater flexibility in the timing of manure applications and adoption of conservation practices such as cover cropping.
With proper installation and nutrient management, phosphorus (P) concentrations in tile drainage water are typically substantially lower than in surface water runoff. In addition to enhanced crop production and soil quality, tiling can reduce soil erosion and total P losses in fields that experience surface runoff. Tiling has come under increasing scrutiny for its role in P export from farm fields, particularly within the past 10 years. However, few long-term, year-round, side-by-side comparisons of tile-drained and undrained fields have been performed in Northern New York.
In 2018, with funding from the Northern New York Agricultural Development Program (www.nnyagdev.org), an edge-of-field monitoring project was initiated on two adjacent 6-acre farm fields in Keeseville, NY. Both fields were primarily composed of a somewhat poorly drained silt loam and had the same cropping and management history. Both fields were also managed the same throughout the study, save that one of the fields was tile-drained (Field TD) just prior to the study. The other field (Field UD) only had surface drainage improvements, which were also done in the tile-drained field to allow a single collection point for surface runoff in each field.
Surface runoff from both fields and tile drainage from the tiled field was collected with automated sampling equipment that adjusted sampling frequency in response to flow rates. Sampling was conducted continuously, year-round to characterize the water quality across the entire year, with the exception of equipment failures. Both fields were planted with corn for silage and received tillage-incorporated manure applications within 24 hours of planting, supplemented by commercial fertilizer when necessary to satisfy the crop’s nutrient requirements.
From 2018 through 2022, there was 44% more total drainage from TD (surface + tile drainage) than UD (surface drainage only). This is not surprising as the purpose of tile drainage is to increase the drainage of water from the fields. However, tile drainage typically greatly reduces surface runoff, and this was observed in our study, as UD generated twice as much surface runoff as TD.
Despite the increased drainage volumes, water quality improvements can be achieved in many cases when surface runoff is reduced following the installation of systematic tile drainage. We did observe this pattern, as the concentrations were much higher and the majority of the P load from TD was transported in surface drainage. Although surface drainage only generated 37% of the total field drainage in TD, it was responsible for 81% of the P exported from the field. Ultimately, the reduced rates of surface runoff resulted in 22% less P lost from TD than UD. It is important to note that as seen in the graph of P loads, regardless of drainage differences, both fields lost very low rates of P, with averages of 0.21 lb/acre/yr and 0.27 lb/acre/yr of P lost by TD and UD, respectively, across the five-year study. These values represent less than 2% of all the P that was applied to the field throughout the study in manure or commercial fertilizer.
In next month’s Farm Report issue, I’ll wrap up a few more key points from this phase of the project, and then introduce what is in store for the next several years at this site.