Subsurface drainage improves row crop production but also short circuits nitrate-nitrogen (NO 3-N) pathways in the soil with significant losses to surface waters. The objective of this study was to evaluate the effect of shallow, controlled, conventional, and undrained drainage treatments on depth to water table, drainage volume and NO 3-N loads, soil water content and storage in the soil profile, and crop yields. This research was conducted at the Iowa State University Southeast Research Farm near Crawfordsville, Iowa, from 2007 to 2015. We report on years five through nine here. The site consisted of eight large field plots with each of the four drainage treatments replicated twice. One-half of each plot was planted with corn (Zea mays L.) and the other half with soybeans (Glycine max [L.] Merr.). The corn and soybean halves were rotated every year in accordance with a typical corn-soybean rotation. The undrained treatment had a shallower water table than the other treatments and had a significantly higher number of days during the growing season when the water table was within 30 cm (12 in) of the ground surface than the other treatments. However, there was no difference in soil water contents in the top 80 cm (31.5 in) of the soil profile during the growing season between drainage treatments. Over the five-year study, controlled and shallow drainage reduced annual subsurface flows by 60% and 58%, respectively, while also reducing NO 3-N loads by 61% and 49%, respectively, as compared to the conventional drainage design. Crop yields were similar along the drainage designs but significantly lower in the undrained treatment. This study highlights the effectiveness of shallow and controlled drainage to reduce NO 3-N loads.
ABSTRACT. Developing drainage water management (DWM) systems in the Midwest to reduce nitrogen (N) transport to the northern Gulf of Mexico hypoxic zone requires understanding of the long
over the whole season from mid-April to the end of September Volumetric water content (VWC) for period 1 at 10 cm in (a) corn plots, 2015 (b) soybean plots, 2015 (c) corn plots, 2016 and (d) soybean plots, 2016, at 20 cm in (e) corn plots, 2015 (f) soybean plots, 2015 (g) corn plots, 2016 and (h) soybean plots, 2016 and at 40 cm in (i) corn plots, 2015 (j) soybean plots, 2015 (k) corn plots, 2016 and (l) soybean plots, 2016; period 1 includes data from mid-April to mid-May Volumetric water content (VWC) for period 2 10 cm in (a) corn plots, 2015 (b) soybean plots, 2015 (c) corn plots, 2016 and (d) soybean plots, 2016, at 20 cm in (e) corn plots, 2015 (f) soybean plots, 2015 (g) corn plots, 2016 and (h) soybean plots, 2016 and at 40 cm in (i) corn plots, 2015 (j) soybean plots, 2015 (k) corn plots, 2016 and (l) soybean plots, 2016; period 2 includes data from mid-May to mid-June Volumetric water content (VWC) for period 3 at 10 cm in (a) corn plots, 2015 (b) soybean plots, 2015 (c) corn plots, 2016 and (d) soybean plots, 2016, at 20 cm in (e) corn plots, 2015 (f) soybean plots, 2015 (g) corn plots, 2016 and (h) soybean plots, 2016 and at 40 cm in (i) corn plots, 2015 (j) soybean plots, 2015 (k) corn plots, 2016 and (l) soybean plots, 2016; period 3 includes data from July 1 to mid-August Mean daily soil temperature at 10 cm in (a) corn plots and in (b) soybean plots, at 20 cm in (c) corn plots and in (d) soybean plots and at 40 cm in (e) corn plots and in (f) soybean plots; includes data from period 1 Mean daily soil temperature at 10 cm in (a) corn plots and in (b) soybean plots, at 20 cm in (c) corn plots and in (d) soybean plots and at 40 cm in (e) corn plots and in (f) soybean plots; includes data from period 2 vii ACKNOWLEDGEMENTS First and foremost, I would like to thank my major professor Dr. Matt Helmers. He has served as a role model, mentor and friend throughout my time at Iowa State. I am beyond grateful to have been able to work with someone as compassionate about their work as he is. He has helped spark my strong interest in agriculture and water quality research. Secondly, I would like to thank Carl Pederson for his expertise in all areas, especially his wealth of knowledge in the production and operation areas of agricultural systems. Also, I would like to thank my program of study committee, Dr. Michael Castellano and Dr. Robert Malone for their critique and guidance. Specifically, I would like to thank Dr. Castellano for his excellent and truly thought-provoking teaching of the highly complex agroecosystem cycles. Also, I cannot thank Dr. Malone enough for the time and effort that he has provided; his help has vastly advanced my knowledge of agricultural simulation modeling and agroecosystems in general. I would also like to thank Adam Martin-Schwarze for multiple hours of help with my statistical analysis. I would like to thank members of the Ag Water Management research team for their help with data collection. Constance Cannon was particularly helpful and a great friend throughout my time at Io...
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