Nitrogen (N) losses from agricultural tile drainage systems are environmental and economic losses for producers. This field study quantified N losses from three reps of shallow (SD), deep/conventional (DD), and controlled drainage (CD) on farmland in Nova Scotia. Drainage systems were under corn and alfalfa–oats–clover production. Outflow water and gas samples were obtained and analyzed for nitrate and nitrous oxide. Nitrate-N loads were 5.0, 11.1, and 6.4 kg ha−1 in 2015; 1.8, 6.7, and 2.8 kg ha−1 in 2016; and 0.74, 1.8, and 1.6 kg ha−1 in 2017 for SD, DD, and CD, respectively. Controlled drainage reduced NO3−-N loading by 42.3%–58.2% when compared with the conventional/DD in 2 of 3 yr of study, whereas SD was found to reduce NO3−-N loading by 54.9%–73.1% compared with DD in all years studied. Total NO3−-N losses in this study were measured during the growing season (1 Apr. to 31 Oct.); the magnitude of NO3−-N losses and treatment effects may vary if studied year-round. Nitrous oxide fluxes were variable and low in magnitude throughout the study. Cumulated N2O losses were <1% of the applied N for all drainage types. Controlled drainage increased yields compared with SD and DD. The use of CD in the region could aid in reducing climate stresses, as well as overall NO3−-N loads exiting drainage systems and may enhance crop yields compared with conventional systems. Future studies on dissolved N2O losses from drainage water may provide important insight into whether dissolved N2O losses exceed surface emissions.
Improving plowing management of high nitrogen (N) containing crops is essential in reducing both environmental and economic losses. The timing of plowing may be an important soil and nutrient conservation practice. A field study on a 3 yr potato rotation was conducted in Prince Edward Island, Canada to examine the effects of plow time on corresponding N losses of nitrate-N (NO3--N) and nitrous oxide (N2O). The study site consisted of nine tile drained plots (12 m spacing) with three treatments of plow time; early fall (EF), late fall (LF) temperature based, and the following spring (S) plow. The cropping rotations consisted of barley under-seeded with red clover in yr 1, red clover in yr 2, and Russet Burbank potatoes in yr 3. Each tile drained plot fed into a sample collection station where 50 mL water samples were obtained during flow events and analyzed for NO3--N. Nitrous oxide samples were also simultaneously obtained from the soil surface throughout the monitoring period using a static chamber methodology. Cumulative NO3--N loads over the 3 yrs were found to be reduced at 14.3 and 19.9 kg ha-1 for LF and S respectively, when compared to the EF plow at 24.4 kg ha-1. Nitrous oxide losses were variable and low in magnitude throughout the study (0.04-1.2% of the N applied). Overall, findings from this research suggest that the timing of plowing could be considered when trying to minimize N losses via tile drainage effluent. When considering NO3--N total loads during the rotation period, LF had reduced losses compared to EF in all years of the study. Late fall reduced N2O losses in 1 year by 38.2% compared to S, likely due the incorporation of red clover legume crop. Yields were found to be similar throughout treatments and cropping years, although LF was found to have 2 and 3-fold significant increases in yield of 10 oz potatoes vs. EF and S, respectively. Findings generated from this study will provide nutrient management and environmental farm planners, as well as producers with useful information for improving current management strategies within agricultural drainage systems.
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