A synthesis and comparative evaluation of factors influencing the effectiveness of drainage water management

Abstract

Viable large-scale crop production in the United States requires artificial drainage in humid and poorly drained agricultural regions. Excess water removal is generally achieved by installing tile drains that export water to open ditches that eventually flow into streams. Drainage water management (DWM) is a conservation practice that allows farmers to artificially raise the outlet elevation of a field's drain tile and can reduce nutrient loss during wet periods by storing more water in the field. We intended to assess the effectiveness of DWM to reduce drainage discharge and nutrient loads and additionally identify predictor variables that influence DWM effectiveness. We compared managed (i.e., DWM) and free draining records using paired t-tests, and identified factors associated with DWM effectiveness using a multiple linear regression approach. T-test results indicated that DWM was highly effective in reducing drainage water discharge and nutrient losses via drain tiles as tile discharge volumes were reduced on average 46%, while tile nitrate loads were reduced by 48%. In addition, total phosphorus and dissolved reactive phosphorus loads were reduced by 55% and 57%, respectively. Based on regression results, we found that several aspects of farm and tile drain management were associated with DWM effectiveness, while site specific landscape characteristics were less likely to predict effectiveness. While DWM is effective as a conservation practice to reduce discharges of water and nutrients from drain tiles, we also identified several knowledge gaps. Future research should investigate effects of DWM on water and nutrients lost in other pathways such as surface runoff, preferential flow, groundwater recharge and biological uptake, and also focus more attention on phosphorus as there is a paucity of research on this topic.

Controlled Drainage as a Targeted Mitigation Measure for Nitrogen and Phosphorus

“…The impact of CD on P concentrations in drain water has not been as widely studied as the impact on N according to a recent review by Ross et al (2016). A concern related to CD is that the elevation of the groundwater level will create conditions sufficiently reduced for Al‐ or Fe‐bound PO 4 3− to be released when mineral oxides are reduced.…”

“…Another less intensively studied aspect of CD is the effect on P (Ross et al, 2016), and studies have shown promising results with P retention from 40 to 95% compared with conventional drainage levels. However, it is a concern that CD might increase dissolved PO 4 3− loss as reduced conditions can lead to PO 4 3− desorption from hydrous iron oxides if Fe 3+ is reduced to Fe 2+ (Kadlec and Wallac, 1996).…”

Linking Soil Phosphorus to Dissolved Phosphorus Losses in the Midwest

“…However, for fields with elevated STP (>75 to 80 ppm M3P), attainment of water quality goals may only be addressed through other measures or a combination of practices including drawdown (Withers et al, 2014; Rowe et al, 2016) or a one‐time inversion tillage if severely stratified to increase the buffering capacity of the upper layers of the soil (Sharpley, 2003; Baker et al, 2017). In addition to drawing down STP or implementing inversion tillage, gypsum (Chardon et al, 2012; King et al, 2016) and controlled drainage (Williams et al, 2015a; Ross et al, 2016) offer alternative practices to potentially remove or mitigate P loss.…”

A Review of Phosphorus Removal Structures: How to Assess and Compare Their Performance

“…However, this is not always feasible in urban settings, and therefore use of a slow-release P fertilizer is warranted. Last, reduction of runoff and sub-surface drainage volumes in agricultural settings can be achieved through practices such as tile drain flow-control structures and vegetated buffer strips [4,5]. These practices are mostly incompatible with urban watersheds, which are usually highly impermeable and with runoff as the predominant source of water.…”