Nitrogen balances and losses in conservation cropping systems across a tile-drained landscape in Ohio, United States

Authors: Hanrahan, Brittany; King, Kevin; Rumora, Kathryne - Katie; Stinner, Jedediah

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2024
Publication Date: 5/10/2024
Citation: Hanrahan, B.R., King, K.W., Rumora, K.R., Stinner, J.H. 2024. Nitrogen balances and losses in conservation cropping systems across a tile-drained landscape in Ohio, United States. Journal of Soil and Water Conservation. 79:145-154. https://doi.org/10.2489/jswc.2024.00055.
DOI: https://doi.org/10.2489/jswc.2024.00055

Interpretive Summary: In the agricultural Midwestern US, cropping systems are generally defined by continuous corn (Zea mays L.) or conventional rotations of corn and soybean (Glycine max L.). These cropping systems have short growing seasons and receive large inputs of nitrogen (N) fertilizer, ultimately resulting in surplus N in the soil profile that can be leached to adjacent and downstream surface waters. Implementing conservation crop rotation involves growing a series of crops in the same field over a given time period. As a result, conservation crop rotation has the potential to reduce the length of time when the ground is bare (by extending the growing season) and increase the diversity of crops planted in a field, ultimately enhancing N retention or demand. In this study, we calculated N balances (Inputs – Outputs) in agricultural fields with corn-soybean rotations (CS; n = 18) and corn-soybean-wheat rotations (CSW; n = 12) to compare patterns of N surplus (i.e., N balances greater than zero) and deficit (i.e., N balances less than zero) among crops and between the two rotations. We also examined crop- and rotation-specific patterns of N losses, as both nitrate (NO3--N) and total N. We found that N inputs and balances were greatest in fields planted with corn regardless of rotation, followed by fields planted in wheat and soybean. However, N losses, as both NO3--N and TN were least in fields with wheat. Average annual N balance was also greater in fields with CSW rotation compared with CS, though N losses were not significantly different between fields in the two rotation types. Taken together, these results suggest that including wheat into the corn-soybean rotation has the potential to address pools of surplus N and subsequently reduce N losses from agricultural fields.

Technical Abstract: In the agricultural Midwestern US, cropping systems are generally defined by continuous corn (Zea mays L.) or conventional rotations of corn and soybean (Glycine max L.). These cropping systems have short growing seasons and receive large inputs of nitrogen (N) fertilizer, ultimately resulting in surplus N in the soil profile that is susceptible to leaching to adjacent and downstream surface waters. Implementing conservation crop rotation, which involves growing a series of crops in the same field over a given period, has the potential to reduce periods of bare ground (i.e., lengthening the growing season) and increase the diversity of crops planted in a field, ultimately enhancing N retention or demand. In this study, we calculated N balances (Inputs – Outputs) in agricultural fields with corn-soybean rotations (CS; n = 18) and corn-soybean-wheat rotations (CSW; n = 12) to compare patterns of N surplus and deficit among crops and between the two rotations. We also examined crop- and rotation-specific patterns of N losses, as both nitrate (NO3--N) and total N. Using data from all individual years (n=169), we found that median N inputs were greatest in fields planted with corn regardless of rotation (279 kg N ha-1 for CSW corn and 214 kg N ha-1 for CSW corn), followed by fields planted in wheat (145 kg N ha-1) and soybean (120 kg N ha-1 for CS soybean and 113 kg N ha-1 for CSW soybean). Subsequently, median N balance was greatest in fields planted with corn (112 kg N ha-1 for CSW corn and 51 kg N ha-1 for CS corn) and indicated surplus N in the soil profile. Median N balance was lower in fields planted in wheat (-1.3 kg N ha-1) and soybean (-110 kg N ha-1 for CS soybean and -92 kg N ha-1 for CSW soybean) and indicated N deficit. Median N losses, as both NO3--N and TN, showed a slightly different pattern such that median N loss was least in fields planted with wheat (8 and 11 kg NO3--N and TN ha-1, respectively) and soybean (18 and 21 kg NO3--N and TN ha-1, respectively, for CS soybean and 17 and 23 kg NO3--N and TN ha-1, respectively, for CSW soybean) and greatest in fields planted with corn (31 and 35 kg NO3--N and TN ha-1, respectively, for CS corn and 27 and 34 kg NO3--N and TN ha-1, respectively, for CS soybean). Comparing annual averages between the rotation types revealed that the medians of average annual N inputs and outputs were similar between the CS and CSW rotations. However, the median of average annual N balance was significantly greater in CSW fields (median = 14 kg N ha-1) compared with CS (median = -29 kg N ha-1) yet the medians of average annual N loss were generally lower, though not significantly, in CSW fields compared with CS (e.g., 19 kg NO3--N ha-1 for CSW vs 22 kg NO3--N ha-1 for CS). Taken together, these results suggest that including wheat into the corn-soybean rotation has the potential to address pools of surplus N and subsequently reduce N losses from agricultural fields.