Location: Soil and Water Management Research
Project Number: 5062-11120-001-030-I
Project Type: Interagency Reimbursable Agreement
Start Date: May 2, 2024
End Date: May 1, 2029
Objective:
1. Quantify effects of combined management practices to reduce multiple vectors of reactive nitrogen emissions from fertilized corn cropping systems. 2. Conduct microcosm experiments combined with modeling to improve model algorithms representing soil nitrogen loss pathways. 3. Measure temporal variability of nitrous oxide emissions from stream and ditch systems draining agricultural land and quantify controlling factors for those emissions.
Approach:
Objective 1: The effects of combined management practices for reducing N2O emissions and their simultaneous impact on multiple vectors of reactive N loss including nitric oxide and ammonia gaseous fluxes and nitrate leaching below the root zone will be addressed using the replicated research plots located on the St. Paul campus. High frequency sampling using both manual sampling as well as a highly instrumented automated chamber system will be facilitated by the close proximity (~ 1 km) of the plots to ARS labs. The non-N2O loss vectors will be quantified separately as well as converting them to indirect N2O emissions using IPCC emission factors. This approach will also allow for estimation of total direct + indirect N2O emissions for each combination of practices. The stacked practices will include different combinations of (i) modified N source, (ii) amendments (inhibitors, stimulants or other additives), (iii) placement, (iv) timing, and (v) N rate. The goal of practice selection will be to achieve the same or greater grain yields at an N rate that is at least 15% lower than the Univ. of Minn. extension recommended N rate for the site. Each combination of practices will be evaluated for a minimum of two consecutive growing seasons and will be reassessed and modified regularly over the course of the funded period.
Objective 2: In parallel with the above plot-scale studies, controlled soil microcosm experiments will also be conducted at the nearby ARS labs. These studies will focus on quantifying the contribution of specific microbial processes and/or chemical substrate levels on the production of N2O, NO, NH3 and/or NO3. The goal here will be to define and/or refine specific mathematical algorithms representing the kinetics of reactive N production. Such algorithms can potentially be incorporated into N cycling or larger ecosystem models and will initially be used to test and refine the two-step (2SN) model which accounts for N mineralization, nitrification (both steps), volatilization, ammonium sorption, nitrite toxicity, and microbial inhibitor effects on N2O and NO production at varying temperature. These experiments will utilize a unique incubation system that simultaneously quantifies six reactive N species under varying temperature and moisture regimes.
Objective 3: Primary focus for this work will be in two agricultural watersheds located in south-central Minnesota: High Island Creek and Crane Creek. We have previous experience working in these watersheds that will help to provide context for new N2O flux data. Additionally, we have continuous monitoring data for a fixed location in High Island Creek that will complement our periodic spatial data. Repeated sampling campaigns will depend upon field conditions but will occur roughly every two weeks during ice-free conditions when watershed flow levels permit safe paddling with our packraft mobile platform. Additional water measurements will focus on parameters expected to be important explanatory variables for N2O production; these measurements include concentrations of nitrate, dissolved organic carbon, dissolved oxygen, and turbidity.
