Location: Soil and Water Management Research2011 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
A new field experiment has been initiated by vegetatively propagating kura clover into a 17-ha irrigated field. Initial soil samples have been collected and analyzed for total organic C and N, and a plot plan has been devised. The use of biomass resources for energy provides opportunity to reduce dependence on legacy carbon. One strategy to increase production of biomass for energy is to expand the practice of winter cover cropping to affect carbon conversion both prior to, and after, the main summer crop. We have developed a modeling method to estimate aboveground biomass fixed by a winter rye cover crop at the county level throughout the U.S. Corn Belt. This method has been applied to the Corn Belt of China. Headspace thermal desorption analyses were conducted on 76 different biochars to assess the sorbed organic compounds on the biochar as potential mechanistic drivers for the soil system’s response to biochar additions, in particular on greenhouse gas production. There was large variability observed in this data set, indicating that even biochars created from the same feedstock and identical production parameters can have different sorbed organics. This suggests that the post-production handling and processing of the biochar could be a vital component to the overall soil system response. A literature review of existing black carbon mineralization rates were compiled and observed that the oxygen to carbon (O:C) ratio was an important facet determining the rate of mineralization, with lower O:C biochars possessing slower mineralization rates. This is an important characteristic for the biochar to sequester carbon. Field plots were established in Spring 2011 for examining the impact of both biochar and non-charred feedstock additions to soils. Initial soil sampling was conducted and these samples are currently being analyzed. Laboratory incubations are awaiting the creation of the requested temperature dependent biochar (from USDA-ARS lab in Florence, SC). These biochars will be available towards the end of 2011. Initial samples of various biochars are being screened for organic compounds, including volatile, semi-volatile and non-volatile compounds. A particular focus is on polyaromatic hydrocarbons (PAHs) due to the potential human health implications. This is being performed in-house as well as with outside certified laboratories for sample confirmation. These results will be used to guide selection of the biochars for the greenhouse incubations. A manuscript detailed the initial observed variability of volatile organic compounds on biochars is in preparation. Some of the preliminary nitrification-incubation experiments have been done looking at pH buffering and N addition requirements and conditions. Progress was made in development of the two-step nitrification model with inhibition kinetics.
1. Winter cover crop and residue biomass potential. Biomass sources for biofuels include winter cover crops and crop residues. Cover crops also extend the effective growing season and increase the potential for carbon sequestration while also scavenging nitrogen remaining in the soil after the main growing season. A crop growth model developed by an ARS scientist in St. Paul, MN was used together with a GIS-based regression model to estimate the biomass potential of (i) a winter rye cover crop grown in corn cropping areas of China, and of (ii) corn, wheat, and rice residues for China. The areas where the major crops were grown in China were determined from geographic data. The range of winter rye biomass calculated was 12 to 26 million tons. The crop residue estimate was based on land area, yield values, and the ratio of grain to biomass for each of the major crops – corn, wheat, and rice. The results indicated that 400 million tons of residues are available annually in China from these three crops. The research will benefit researchers and policymakers by putting the size of winter cover crop and agricultural residue biofuel opportunities in perspective with other biofuel options in the world’s most populous country. The results will also be applicable to other parts of the world, including the U.S., that have similar soils, climate, and cropping systems to the systems examined in this research.