Impact of Plow Timing on Simultaneous Nitrogen Losses in Potato Production Systems Using Conventional Tillage Practices

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.