Location: Soil and Water Management Research2013 Annual Report
1a. Objectives (from AD-416):
1. Develop and test systems for sustainable co-production of food and fuel, as a contributor to the ARS Renewable Energy Assessment Project (REAP). 2. Develop guidelines for the optimization of soil fertility and C sequestration using organic and biochar amendments, for field and specialty crops. 3. Enable reduced N2O emissions from fertilized cropping systems through improved understanding of controlling mechanisms, as a contributor to the ARS Greenhouse Gas Reduction through Agricultural Carbon Enhancement network (GRACEnet).
1b. Approach (from AD-416):
Field experiments will be conducted at three locations, each using 3 treatments: zero, intermediate, and full stover removal. We will measure soil organic carbon (SOC) changes and gas exchange. Research will also be conducted at the UMN’s Rosemount Research and Outreach Center (ROC) and on private farm fields in MN. Research at Rosemount will take place in two 20 ha fields with similar soil types, one managed as a conventional corn-soybean rotation; the other in a corn-soybean rotation, but with winter rye cover crop seeded by helicopter in late summer. Latent and sensible heat flux and net ecosystem exchange of CO2 will be measured by eddy covariance. Yield and ancillary soil, physiological and micrometeorological variables will also be measured for 4-years. Soil sampling for SOC analysis will be conducted biennially. Data will be used to test a model of rye production and water use (RyeGro). Field research will also be conducted at Rosemount MN and Arlington WI, supplemented by greenhouse research in St. Paul. Four treatments will be evaluated using a completely randomized design with 3 replications: (i) control, (ii) biochar, (iii) biochar plus manure, and (iv) manure. Biochar will be applied at 20,000 lb ac-1. Three other biochar treatments, derived from macadamia nut, wood pellet, and lump hardwood charcoal, will also be evaluated. Biochar production temperatures will be varied according to constant heating time and thermal time equivalency tests. Experiments will be conducted to examine impact of post-processing of biochar by thermally or chemically activation. All biochars will be analyzed for elemental composition, surface area, thermal stability, and CEC. Incubations will assess the impacts of biochar amendments on GHG production. For the greenhouse studies, 5 different specialty crops will be investigated with respect to biochar impacts on germination, growth, and uptake of volatile chemicals. Lab incubation experiments will be conducted to evaluate the inhibition of ammonium and nitrite oxidation rate due to the presence of free ammonia and free nitrous acid. Three different soils used for corn production in MN, IA, and eastern Canada will be examined. The methods will be adapted from procedures used to quantify nitrification inhibition kinetics in wastewater. Parameters obtained in the lab experiments will be incorporated into previously developed nitrification and N2O emissions models that account for both steps of nitrification, N2O production pathways, microbial N2O reduction, and gaseous diffusion. Plot experiments will be conducted over two consecutive growing seasons at the UMN ROC in Rosemount, MN in long-term research plots split into subplot treatments. Each main plot will first be randomly sub-divided by N rate so that each subplot will receive the same total N rate during the growing season, with N rate levels of 0, 7.5, 15, 20 and 25 g N m-2. Each N rate treatment will then be randomly sub-divided into two timing treatment sub-subplots consisting of (a) a single pre-plant urea application, or (b) two split post-plant urea applications. Soil-to-atmosphere N2O fluxes will be measured using chamber methods.
3. Progress Report:
Objective 1: Three years of automated N2O data from field experiments examining effects of stover removal from corn cropping systems have been analyzed; corresponding results were presented at the National Sun Grant Conference and a publication has been prepared. An aerial seeding experiment was completed and a manuscript was submitted to Agronomy Journal. An experiment is currently underway in which we are comparing biomass and grain yields in the following treatments: conventional rainfed corn, conventional irrigated corn, rainfed corn in kura clover living mulch, and irrigated corn in kura clover living mulch. Objective 2: The second year of field measurements examining the impact of biochar addition to soil on corn grain yield, soil C, and GHG emissions has been completed and the third year was initiated. Results to date indicate reduced mitigation potential of biochar with exposure time in the field. We have also found that pre-composting the biochar reduces the quantities of sorbed organics present and the N2O mitigation potential of the biochar. In soils amended with mixtures of composted and non-composted biochars, greenhouse gas production decreased as the levels of char-associated organic compounds increased. A manuscript detailing this work has been submitted. Plant growth in response to biochar amendment to soil has been monitored in greenhouse and field plots. Collaborations have been established with the University of Minnesota to examine effects of the liquid phase of the pyrolysis process and its corresponding impact on plant growth. The first year of data has been collected and is currently being analyzed. Objective 3: Lab incubation experiments quantifying nitrification dynamics in different soils including soils from New Zealand are continuing. To date we have observed high degree of correlation between cumulative nitrite intensity and cumulative nitrous oxide emissions. We have also observed large differences in nitrite intensity among different soil types amended with the same amounts of urea, and we are investigating which chemical and/or microbial properties are responsible reasons for these differences. We have incorporated new features into the N cycling model including urea hydrolysis and associated pH dynamics, liquid-solid partitioning of the ammonium ion and its effects on ammonium oxidation rates and free ammonia toxicity, and the potential toxicity effects of the nitrite ion and/or nitrous acid species. We completed the second consecutive season of a replicated plot field experiment in Rosemount, MN to examine effects of fertilizer addition rate (6 levels) and timing (single vs. three split applications) on N2O emissions under corn grown in a monoculture and in a corn/soybean rotation.
1. Publication of international guidelines for improved nitrous oxide emissions measurements. Soil nitrous oxide emissions are in many cases the largest component of the greenhouse gas impact of agricultural systems. However, measurements of nitrous oxide fluxes are highly sensitive to the methods deployed and there is currently wide variation in methodologies. Working as part of an international team of experts from 10 countries, ARS scientists from St. Paul, MN and Ames, IA developed methods guidelines that are being distributed internationally via the website of the Global Research Alliance. These guidelines will be used by researchers around the world and will result in more accurate and precise measurement of agricultural nitrous oxide emissions from croplands and grazing lands.
2. Soil nitrite dynamics explain fertilizer management effects on nitrous oxide emissions. It is typically assumed that the dependence of nitrous oxide emissions on soil nitrogen availability is best quantified in terms of ammonium and/or nitrate concentrations. In contrast, nitrite is seldom measured separately from nitrate despite its role as a central substrate in nitrous oxide production. We examined the effects of three fertilizer sources and two placement methods on nitrous oxide in corn over two growing seasons. Cumulative nitrous oxide emissions were well-correlated with soil nitrite levels but not with levels of nitrate or ammonium. By itself, nitrite intensity explained more than 44% of the overall variance in cumulative nitrous oxide emissions. These results show that practices which reduce nitrite accumulation have the potential to also reduce nitrous oxide emissions, and that separate consideration of nitrite and nitrate dynamics can provide more insight than their combined dynamics as typically quantified. These findings therefore provide new criteria for land managers to assess how practices such as fertilizer placement and chemical formulation can be modified to reduce N2O emissions.
3. Development of an automated system for remote nitrous oxide flux measurements. Research on ways to reduce nitrous oxide production has been hampered by a lack of reliable data because it is episodic in nature and difficult to measure. We developed an automated system capable of continuous, unattended measurement that is powered by solar panels and a wind turbine suitable for deployment in remote field locations. The system uses an analyzer that is much less expensive than previous analyzers, coupled to commercially available automated chambers originally developed to measure soil respiration. Results demonstrate that the system is accurate and reliable, and can measure nitrous oxide production continuously over the course of a growing season. This system will be used by scientists studying the impact of management practices on nitrous oxide emissions.
4. Weathering reduces greenhouse gas mitigation potential of biochar. Studies have shown conflicting results regarding the effectiveness of biochar as a soil amendment for reducing greenhouse gas (GHG) emissions. Our results showed that the mitigating impacts of biochar for GHG suppression appear to be of limited duration. Weathered biochar did not suppress N2O production compared to un-amended soils. Furthermore, weathering also caused an increase rate of mineralization of the biochar. These findings provide additional insight into the mechanisms of biochar effects on soil N cycling and will assist scientists and engineers in developing improved biochars to minimize GHG emissions.
Van Kessel, C., Venterea, R.T., Six, J., Adviento Borde, A., Linquist, B., Van Groenigen, K. 2013. Climate, duration, and N placement determine N2O emissions in reduced tillage systems: a meta-analysis. Global Change Biology. 19(1)33-44.