Project : USDA ARS

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Research Project: Developing Aspirational Practices Through Improved Process Understanding to Protect Soil and Air Resources and Increase Agricultural Productivity in the Upper Midwest U.S.

Location: Soil and Water Management Research

2024 Annual Report

Objectives
Objective 1. Evaluate and develop innovative cropping systems and management practices to increase the resiliency and decrease the environmental impacts of agricultural systems. a. Develop management practices that address the key impediments to adoption of kura clover living mulch systems for corn production. b. Quantify the agronomic and environmental performance of corn grown with and without the use of novel soil amendments in integrated management systems. Objective 2. Improve fundamental understanding and predictability of nitrogen and carbon transformation processes to improve crop nutrient use efficiency and reduce nutrient losses, especially through engineered solutions. a. Reveal chemical mechanisms of N and C transformations occurring with biochar amendments and develop guidance for agronomic use. b. Quantify fundamental N process rates following urea addition to soil with and without soil amendments and incorporate missing processes into a dynamic model.

Approach
This project will address key challenges facing corn producers in the upper Midwest U.S., which include the need for strategies that extend vegetative cover for longer periods and reduce reactive nitrogen losses to aquatic systems and greenhouse gas emissions. These challenges will be addressed through a combination of field, lab, and modeling-based studies structured around two main objectives and four integrated sub-objectives. Objective 1 will utilize field and laboratory studies to evaluate and develop innovative cropping systems and management practices to increase the resiliency and decrease the environmental impacts of agricultural systems. Sub-objective 1A will evaluate the feasibility of overseeding kura clover into an existing alfalfa stand to maintain forage productivity during the kura clover establishment period and determine if reduced intensity tillage can produce early corn growth similar to rotary zone tillage if combined with injected anhydrous ammonia as a nitrogen source. Sub-objective 1B will quantify the agronomic and environmental performance of corn grown with and without the use of novel soil amendments in integrated management systems. The overall aim of Objective 2 is to improve fundamental understanding and predictability of nitrogen and carbon transformation processes to improve crop nutrient use efficiency and reduce nutrient losses. Sub-objective 2A will use laboratory studies to reveal the chemical mechanisms of nitrogen and carbon transformations occurring with biochar amendments which will be used to develop guidance for the agronomic use of biochar. Sub-objective 2B will quantify fundamental nitrogen process rates following urea addition to soil with and without soil amendments and incorporate missing processes into a dynamic nitrogen cycling model. This research will increase our understanding of fundamental soil processes to allow improved prediction of agronomic and environmental outcomes and generate recommended practices for corn producers and policy makers that utilize innovative cover crops, row establishment systems and soil amendments to maintain productivity, increase climate resilience and soil carbon storage, and decrease environmental risks.

Progress Report
In support of Sub-Objective 1A, experiments were designed to quantify the impact of management practices on the performance of corn grown in a kura clover living mulch (KCLM) system. Experiments are underway at University of Minnesota research fields in Lamberton, Minnesota and Rosemount, Minnesota that are evaluating the suitability of two row establishment methods: (1) banded herbicide application and (2) strip tillage. Additionally, three different planting dates are being tested to help develop guidelines for farmers interested in applying KCLM as a conservation practice. Data from the 2022 and 2023 growing seasons have been collected including: corn and kura biomass, and corn grain yield. A third year is underway in 2024. The two years with complete data (2022-23) were characterized by extreme drought and corn grain yield was less than yields observed in nearby business as usual (BAU) fields. Preliminary results indicate that earlier planting dates performed better than later planting dates, but all kura clover treatments performed more poorly than adjacent BAU fields. These results have been important for demonstrating that a permanent living mulch can compete with corn for soil moisture during dry years and can help to identify which may be suitable for KCLM. The 2024 growing season has had adequate precipitation so far; we anticipate that current weather conditions will provide a good contrast to the previous two drought years. During 2022 and 2023, samples of kura clover aboveground biomass were collected from experimental plots on a weekly basis. These data are being used to develop generalized kura clover growth models based on the plant heat unit approach. Preliminary models have been developed and are being updated as additional data become available. In support of Sub-Objective 1B, Goal 1B, a manuscript reporting lab microcosm experiments examining the effectiveness of procyanidin compounds for decreasing soil nitrous oxide (N2O) production was revised and accepted for publication in Applied Soil Ecology. The final publication showed that grape seed extracts (GSE) can effectively inhibit denitrification in soil, that specific GSE chemical components may counteract the overall N2O inhibition effect of procyanidin mixtures, that dose-response to GSE varies with soil cropping history and physical properties, and that GSE application timing relative to urea fertilizer application had no impact on N2O inhibition potential. The lab incubation system was then deployed to investigate greater than expected emissions of N2O observed from kura clover stands in the field. Preliminary results showed that above ground plant material taken from kura clover stands produced large amounts of N2O even when incubated without the presence of any soil. It was also observed that soluble inorganic nitrogen compounds extracted from the plant material during the incubation were positively correlated with the elevated N2O production, indicating a previously unrecognized source that does not depend on direct interaction of plant material with soil. These results are being incorporated into a manuscript. In support of Sub-Objective 1B, Hypothesis 1B, a new field experiment was established in St. Paul, Minnesota to investigate the combined effects of microbial inhibitors, fertilizer application timing, and total nitrogen application rate on soil N2O emissions and corn yield. This experiment is utilizing an automated chamber system for measuring N2O emissions multiple times per day and should reveal valuable information about the temporal dynamics of N2O production that manual sampling cannot generally provide. We are also making measurements in a separate field experiment in southeastern Minnesota being managed by a University of Minnesota collaborator. These experiments are investigating the effects of soybean planting date and tillage regime on soil N2O emissions. Additional progress related to the project objective of measuring soil N2O emissions was made under a new sub-award from Rowbot Systems LLC under a USDA-SBIR grant. This work is continuing the development of a mobile robot for measuring greenhouse gases (GHG) from agricultural fields. Unit Scientists are working with Rowbot Systems to help design a prototype robot equipped with a remotely operated GHG flux chamber and to compare the gas concentrations in robot-collected samples with samples collected manually using conventional chambers. In addition to these field experiments, work is being done by an ARS Headquarters-supported post-doc to complement our efforts to better quantify N2O emissions resulting from agricultural soil management. Small agricultural streams have been shown to be disproportionate sources of N2O in agricultural watersheds. One thing that remains poorly understood is how N2O flux from these small waterways may vary over space and time. This knowledge gap is at least partly driven by the fact that low order ditches and streams are difficult to sample. To address this challenge, we developed a new approach for measuring N2O efflux from agricultural streams by deploying a floating chamber from an inflatable pack-raft capable of navigating small streams. Preliminary results show that N2O flux from stream water can vary by a factor of 2-3 over relatively short distances of stream channel (<200 meters) indicating that localized changes in stream channel biogeochemistry can exert important controls on N2O efflux. In support of Sub-Objective 2A, Goal 2A, laboratory incubations with fresh biochar as well as weathered biochar from the ongoing citizen science efforts were analyzed for their production of NOx gases which consist of nitric oxide (NO) and nitrogen dioxide (NO2). Results showed that the production of NOx gases following exposure to inorganic nitrogen solutions varies among different biochars and was altered (either increased or decreased) by biochar weathering. There is no clear indication as of yet for variables that can reliably predict these responses, although wood feedstocks more commonly exhibited higher NOx production rates compared to non-wood feedstocks. Our investigations have determined that pre-treatment of biochars with hydrogen peroxide does increase the rate of nitrogen transformations, providing some hints as to the underlying mechanisms. Further research is underway examining the responses of commercially available biochars to these treatments. Several collaboration efforts addressing biochar dynamics in soil have also been established. We are actively participating in a cross-location research effort that is examining biochar characteristics across several ARS laboratories. The goal of this work is to achieve insight into the physical and chemical properties of biochar that will improve our understanding of the mechanisms and enable better predictive tools to be developed for forecasting biochar’s impact across differing climates, crops and soil types. A new collaboration with the Univ. of California-Davis has also been established to explore other facets of biochar weathering. Additionally, efforts are underway to further develop collaborative relationships across other federal entities, including NRCS, Forestry Service, and USGS to examine analytical methodologies to forecast biochar’s carbon stability. Research has been completed by ARS Scientists in St. Paul, Minnesota and collaborators addressing the influence of biochar particle size on its weathering in soils. Results have shown that smaller biochar size fractions possessed the largest changes (decreases) in chemical sorption compared to the larger particle sizes. A manuscript is being finalized detailing this advancement. This is an important consideration given the fact that biochar undergoes particle size reduction with tillage and soil management operations. Therefore, the effectiveness of biochar in soil may be greatly reduced with time. Further progress on integrating nitrogen stable isotopes into this research is still hampered by analytical instrumentation issues with the mass spectrometer that are still under investigation by the manufacturer. In support of Sub-Objective 2B, Hypothesis 2B, equations were developed to augment the 2SN model to account for N2O produced by heterotrophic denitrification occurring in anaerobic soil microsites as well as nitrification occurring in aerobic zones which depend on the availability of requisite nitrogen substrates as well as oxygen availability. Coding of the equations into the computer model is ongoing. The 3-dimensional gas diffusion model component was further enhanced to examine the effects of spatially non-uniform N2O production on the accuracy of chambers deployed over a finite segment of the interrow space. The model was augmented to conduct Monte Carlo analyses evaluating the effect of measurement error on the accuracy and precision of competing flux-calculation equations. The nitrogen fixation experiments using stable isotopes have been delayed due to the unavailability of the mass spectrometer as described above.

Accomplishments
1. A new mobile platform to capture the spatial and temporal variability of nitrous oxide (N2O) emissions from waterways. Small agricultural streams have been shown to be disproportionate sources of the greenhouse gas N2O in agricultural watersheds. The emissions arise from soluble nitrogen in water draining from cropped fields. One thing that remains poorly understood is how N2O flux from these small waterways may vary over space and time due in part to the difficulty in accessing lower order ditches and streams across their length. To address this challenge, ARS researchers in St. Paul, Minnesota developed a method for measuring N2O efflux from streams that deploys a floating chamber attached to an inflatable pack-raft capable of navigating small streams. Initial observations show that N2O flux from stream water can vary by a factor of 2-3 over relatively short distances (<200 meters) indicating that localized changes in stream channel biogeochemistry exert important controls on N2O efflux. The new mobile platform has the potential to greatly increase our understanding of the magnitude of stream N2O emissions and their key regulating variables. This improved understanding will support the development of strategies to reduce N2O emissions originating from agricultural practices.

2. Nitrification inhibitors (NIs) can have net negative health and economic impacts if ammonia emissions are not mitigated. The application of NIs to soil can reduce fertilizer-derived emissions of the potent greenhouse gas nitrous oxide (N2O) and emissions of nitric oxide (NO) which forms ozone and particulate matter (PM) pollution. However, NIs can unintentionally increase the volatilization of ammonia (NH3) gas, which is an even more potent precursor of PM compared to NO. ARS researchers in St. Paul, Minnesota in collaboration with scientists at Rice University conducted a study that evaluated the human health impacts of NIs at a national scale for the U.S. considering these trade-offs. An agroecosystem model was used to predict gas emissions with or without the use of NIs. Emissions of N2O were monetized based on the social cost of N2O on climate, while air quality and health models were used to inform the impacts of NO and NH3 emissions. Estimates of net NI impacts were obtained in two ways: (1) based on the agroecosystem model projection, and (2) by multiplying baseline emissions from the agroecosystem model by relative changes in gas emissions reported by global meta-analyses. In both cases, results indicated that NI-induced harms from increased NH3 emissions outweigh the benefits of reducing NO and N2O emissions across all agricultural regions. This study highlights to scientists and regulators the importance of considering multiple pollutants when assessing NIs and underscores the need to mitigate emissions of NH3 as well as N2O and NO.

U.S. DEPARTMENT OF AGRICULTURE

Soil and Water Management Research: St. Paul, MN