Temporal Subsurface Flow Patterns from Fifteen Years in North-Central Iowa

Abstract

Subsurface drainage in the Upper Midwest is of importance to agricultural production. However, proper management of these systems through in-field management, drainage management, or edge of field practices is needed to limit negative environmental impacts particularly from nitrate-nitrogen leaching losses. One management practice being considered is drainage management where the outflow of subsurface drainage is managed to conserve water and decrease the overall outflow of subsurface drainage. To understand how and when drainage management may be utilized in the upper Midwest it is important to review long-term drainage data to understand the timing, duration, and volumes of subsurface drainage in these climates. An ongoing drainage study from north-central Iowa allows for reviewing fifteen years of subsurface drainage which encompasses a range of climatic conditions. This information has been reviewed with the objective of understanding the timing, duration, and drainage volumes considering temporal drainage flow patterns. In particular, the monthly and seasonal flow patterns have been investigated using this long-term drainage record. On this site with a relatively narrow drain spacing of 7.6 m, drainage volume was approximately 40% of the precipitation. The time period from April through June had approximately 50% of the average annual precipitation and approximately 70% of the average annual drainage. In addition, the percent of annual drainage occurring after August 1 was only approximately 7%. The timing of subsurface flow in these areas specifically during the spring coincides with time of planting, crop germination, and early crop development has implications when considering drainage management practices and the effectiveness of these practices to limit flow and therefore nitrate-nitrogen leaching losses. To minimize outflow of drainage water, these drainage management systems would need to allow for adequate flexibility to ensure crop production while effectively managing subsurface drainage flow to potentially minimize the outflow of water.

Dissolved Constituents in Agricultural Drainage Waters

“…4). Flows tend to be strongly correlated with precipitation during the early growing season because the soil is saturated and evapotranspiration is generally lower than precipitation (Helmers et al, 2005). From May 19 to June 26, the cumulative precipitation was 22.71 cm; this precipitation pe-riod corresponds to the cumulative flows observed from May 26 to June 30.…”

“…rtificial subsurface drainage is common in agricultural regions with high water tables and poorly drained soils (Helmers et al, 2005). Modern subsurface drainage systems consist of perforated pipe networks placed below the root zone, typically at a depth of 0.9 to 1.2 m from the soil surface, thereby providing a pathway for water to flow from the upper soil horizons.…”

Modification of a dual‐chamber denitrification bioreactor with a surface water pumping system

“…The inlet of the bioreactor can also experience larger fluctuations in the water level, experiencing periods of drying and rewetting that have also been hypothesized as accelerating woodchip decomposition (Ghane et al, 2018;Maxwell et al, 2019). As most bioreactors in the Midwest region of the United States receive subsurface drainage, there can be periods of no or low flow conditions as the drainage often subsides with crop development (Helmers et al, 2022(Helmers et al, , 2005. With the use of a pumping system, the bioreactor could potentially experience more uniform, consistent flow rates with less variation in the saturation level of the bioreactor, potentially extending the life of the bioreactor.…”

“…Due to the adaptability of the design of denitrifying bioreactors and the need for reductions to nitrate loading for both ecological and human health concerns, additional uses of bioreactor systems warrant study to allow for the treatment of further sources of water. The subsurface drainage flow is often seasonal in the Midwestern region of the United States, with flow subsiding in the summer when the crop water demand is greatest (Helmers et al, 2022(Helmers et al, , 2005. This period of low or no flow conditions presents an opportunity for unique bioreactor designs to be implemented.…”

Corn Yield Increase Under Constant Fertilizer Did Not Reduce Nitrate Export

“…1) that records precipitation through a tipping bucket (Campbell Scientific, Inc., Logan, Utah), backed up by a manual rain gauge generally consulted at the same time as water sampling. Lawlor et al (2008) provided a detailed description of ADW, which other publications from the experiment (Helmers et al, 2005;Singh et al, 2006;Qi et al, 2011;Helmers et al, 2012;Lagzdiņš and Helmers, 2015;Waring et al, 2020;Waring et al, 2022) augmented.…”