Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2011
Publication Date: 12/12/2011
Citation: Kroger, R., Pierce, S.C., Littlejohn, K.A., Moore, M.T., Farris, J.L. 2012. Decreasing nitrate-N loads to coastal ecosystems with innovative drainage management strategies in agricultural landscapes: An experimental approach. Agricultural Water Management. 103:162-166. Interpretive Summary: Following storm events or controlled irrigation releases, runoff water from fields enters ditches which serve as conduits between the field and nearby river, lake, or stream. Installing controlled drainage structures (e.g. weirs) to slow down the water flow in ditches and allow more time for natural processes to degrade or bind nutrients helps improve overall water quality from agricultural lands. Experimental ditches were used to determine how much nitrogen could be decreased in runoff that travelled through a series of weirs before exiting the farming system. Results from this experiment were mixed, due to a nutrient overload in the ditch systems. Ditch systems with weirs increase the travel time for nutrient-rich runoff to reach receiving systems, thereby allowing natural processes to improve the water quality.
Technical Abstract: Controlled drainage in agricultural ditches contributes to a drainage management strategy with potential environmental and production benefits. Innovative drainage strategies including spatially orientated low-grade weirs show promise to significantly improve nutrient (e.g. nitrate-N) reductions by expanding the area available for biogeochemical transformations, as well as providing multiple sites for runoff retention and nutrient reduction. The overall objective of this study was to identify the contributions made by low-grade weirs, an innovative, cost effective drainage management technique which decreased source nitrate-N concentrations and loads to downstream coastal ecosystems. This objective is achieved by assessing, from an experimental standpoint, the effectiveness of weirs in reducing nitrate-N concentrations and loads in replicated ditch systems in Jonesboro AR. Nitrate load reduction rates were approximately 2250 ± 718 mg/hr and 1935 ± 452 mg/hr for ditches with and without weirs, respectively, resulting in mean percent nitrate load reductions of 79 ± 7.5% and 73 ± 9% for ditches with and without weirs, respectively. Although nitrate reductions were substantial in both systems, no significant treatment effect was detected. A stepwise linear regression was performed analyzing the relationship of time + treatment on nitrate concentration. This model explained 31.1% of the variance in nitrate concentration, which indicated a highly significant relationship between nitrate concentration and time + treatment (F = 31.9, p <0.001). Nitrate reductions were significantly different between weir and no weir treatments based on time, however, overloading of both system residence times showed no differences in nutrient reductions. Low-grade weirs show promise in improving nutrient reductions with the capability of increasing residence time in agricultural drainage ditches, and reducing overall outflow loads to downstream systems.