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Title: Subsurface drainage volume reduction with drainage water management: Case studies in Ohio, USA

item GUNN, KPOTI - The Ohio State University
item Fausey, Norman - Norm
item SHANG, YUHUI - The Ohio State University
item WAHL, MARK - The Ohio State University
item GHANE, EHSAN - The Ohio State University
item SHEDEKAR, VINAYAK - The Ohio State University
item BROWN, LARRY - The Ohio State University

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2014
Publication Date: 11/26/2014
Citation: Gunn, K.M., Fausey, N.R., Shang, Y., Wahl, M.D., Ghane, E., Shedekar, V.S., Brown, L.C. 2014. Subsurface drainage volume reduction with drainage water management: Case studies in Ohio, USA. Agricultural Water Management. 149(2015):131-142.

Interpretive Summary: Drainage water management is a new practice developed to reduce water discharge from subsurface drainage systems during certain times of the year by adjusting the outlet level of the drainage system. Reduced water discharge lowers the delivery of soluble nutrients from agricultural fields into streams. Farmer acceptance of the new practice has been slow because the farmer's perceive that there is no return on the cost of installing the practice. Development and operation of a nutrient trading exchange could provide incentive for farmers to adopt the practice as a source of income. In order to trade the undelivered nutrients, there needs to be a way to quantify the reduction in water discharge and nutrient retention. The drainage water management practice was installed and operated on seven farms in Ohio for 3 years in a side-by-side comparison with conventional, unmanaged drainage. Results indicate an outflow volume reduction of 27 to 88% for flow generated by storm events greater than 0.5 inches of precipitation depending on the particular site and timing of the rainfall. This information is important for NRCS, for growers, and for the drainage industry.

Technical Abstract: One of the main contributors to poor water quality in the Mississippi River and aeral increase in the hypoxic zone in the Gulf of Mexico is intensive drainage of the cropland within the watershed. Controlled drainage has been demonstrated as an approach to curb totla drainage outflow and nutrient discharge from rainfed agricultural fields. However, it effects have yet to be demonstrated in the humid region with poorly drainaed soils. This paper reports the results of a three year study on eight agricultural fields in Ohio, where artificial drainage was required for production. Controlled drainage was compared to conventional free drainage for various hydrologic parameters at each site using a paired watershed analysis approach.Flow depths at drainage outlets and rainfall data were collected. Outflow volume per time interval was calculated and summarized for events with precipitation greater than 1.27 cm (0.5 in). Water flowing in the control structures was occasionally sampled and tested for nitrate-N and phosphate-P concentration. Linear relationships established between the outflow volume data from free drainage area and those from controlled drainage area at each site during the free drainage period were used to estimate outflow volumes for controlled drainage area, for precdipitation events considered during the controlled drainage period. The mean estimated volume was compared to the mean observed volume. An estimator of the effect of controlled drainage was calculated for each site and tested for significance at 1%. An outflow reduction of 27 to 88% due to controlled drainage application was observed at the analyzed sites, and for the analyzed precipitation events (p<0.01). Discontinuity of data made it impossible to estimate yearly outflow volumes. The nutrient concentration readings did not necessarily coincide with the discharge events analyzed, making a robust statisticl comparison difficult. However, differences in concentration were not observed between free drainage and controlled drainage, except in a few cases. Based on the conclusions of previous studies, it was implied that an annual reduction in nutrient export may be observed assuming similar reductions it total outflow volume for smaller and more frequent precipitation events throughout the year.