Tillage effects on drainage fluxes and nitrate leaching through unsaturated zone under irrigated corn-soybean rotation

Authors: Jabro, Jalal - Jay; Iversen, William - Bill; Stevens, William - Bart; Sainju, Upendra; Allen, Brett

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2019
Publication Date: 3/1/2019
Citation: Jabro, J.D., Iversen, W.M., Stevens, W.B., Sainju, U.M., Allen, B.L. 2019. Tillage effects on drainage fluxes and nitrate leaching through unsaturated zone under irrigated corn-soybean rotation. Applied Engineering in Agriculture. 35(3):293-300. https://doi.org/10.13031/aea.13127.
DOI: https://doi.org/10.13031/aea.13127

Interpretive Summary: With growing public concerns regarding water quality, researchers are diligently developing management practices that will reduce agrochemical leaching. One device researchers often use to estimate leachate properties is the water sampler that is used to collect soil water in order to measure chemical characteristics of water which has leached through the soil profile. Groundwater pollution with nitrate is one of the major health concern in irrigated areas nationwide and in the semi-arid northern Great Plains region. Scientists at the ARS in Sidney Montana conducted a long-term field study to evaluate the effect of no-tillage (NT) and conventional tillage (CT) practices on seasonal drainage fluxes and nitrate leaching losses below the rootzone in irrigated corn and soybean on sandy loam soil. Sixteen water samplers were placed 90 cm below the soil surface to quantify percolated drainage amounts below the rootzone of corn-soybean rotation under NT and CT practices. They found tillage has no effect on seasonal drainage and nitrate losses under both corn and soybean due to considerable spatial soil variability within the field. Nitrate concentrations in drainage water for four growing seasons exceeded the safe U.S. EPA drinking water standard of 10 mg L-1. These high nitrate concentrations in groundwater may pose a serious health risk to public from agriculture’s impact on groundwater quality. Reducing nitrogen inputs by applying less nitrogen fertilizer and using better nitrogen and irrigation management practice would have reduced nitrate leaching losses from agricultural soils, maintained yield, reduced input expenses, and sustained environmental quality.

Technical Abstract: High levels of nitrate-nitrogen (NO3-N) in the nation’s groundwater are a significant environmental concern. To date no studies have yet evaluated the effects of various tillage practices on percolated drainage and NO3-N fluxes below the rootzone of cropping systems in the northern Great Plains. A field study was conducted to examine and compare the effect of no-tillage (NT) and conventional tillage (CT) practices on seasonal drainage fluxes and NO3-N leaching losses below the rootzone in irrigated corn (Zea mays L.) and soybean (Glycine max L.) on a Lihen sandy loam soil. Sixteen passive capillary lysimeters, PCAPs (75 cm long polyvinyl chloride pipe with a collecting surface area of 0.1 m2) were placed 90 cm below the soil surface to quantify percolated drainage water below the root zone of corn-soybean rotation under NT and CT practices. The study was designed as a randomized complete block with four replications. Drainage and NO3-N fluxes were not significantly affected by the tillage in 2014, 2015, 2016, and 2017 due to substantial spatial variations among lysimeters within each treatment. Average cumulative seasonal drainage depths across 4 years were 22.26 and 34.46 mm for corn and 24.95and 28.16 mm for soybean under NT and CT, respectively. Averaged 4-yr cumulative NO3-N losses were 17.61 and 26.74 kg ha-1 for corn and 25.47 and 23.56 kg ha-1 for soybean under NT and CT, respectively. The mean flow-weighted NO3-N concentrations over 4 years were 63.8 and 70.6 mg L-1 for the NT and CT under corn, respectively, while that from the soybean were 47.2 and 64.9 mg L-1 for the NT and CT, respectively. Nitrate-nitrogen concentrations generally exceed the safe drinking water standard of 10 mg L-1. Reducing N inputs in well-drained soils and using site specific N and irrigation management practices are feasibly required to lower input expenses, reduce N leaching losses and sustain environmental quality.