1a. Objectives (from AD-416):
Past and current farming practices in the dryland region of the Pacific Northwest (PNW, northern Idaho, north central Oregon and eastern Washington) have resulted in excessive soil erosion by wind and water, declining soil organic matter levels, poor N use efficiency and losses of biological diversity. These adverse processes are linked to regional degradation of air, water and soil resources and contribute to GHG emissions that drive climate change. This project addresses knowledge gaps associated with the capacity to understand, predict and mitigate PM10/PM2.5 and GHG emissions from dryland agricultural lands. Objective 1. Characterize key environmental and management drivers of agricultural wind-blown dust and PM10/PM2.5 emissions that will improve process-oriented models and decision aids. Sub-objective 1.a. Determine the relationship between soil wetness/crusting and emission of windblown dust and PM10/PM2.5. Sub-objective 1.b. Determine the biotic factors driving aggregate formation and stability in dryland soils and their influence on windblown dust and PM10/PM2.5 emissions. Sub-objective 1.c. Determine the effect of wind erosion and management practices on soil organic matter (SOM), soil biological communities and other soil characteristics. Objective 2. Develop techniques for identifying sources of PM10/PM2.5 to better associate management practices with PM10/PM2.5 emissions and to corroborate models. Sub-objective 2.a. Determine the efficacy of FAME and tracer methods in discerning soils contained in various mixtures. Sub-objective 2.b. Determine point source soil movement and FAME efficacy using known microbial tracers. Sub-objective 2.c. Determine the effectiveness of using FAME fingerprinting to corroborate the Columbia Plateau regional dust transport model. Objective 3. Characterize roles of environmental and management drivers on soil C and N cycling as factors regulating GHG (N2O, CO2) emissions from agricultural soils. Sub-objective 3.a. Determine soil C sequestration rates and CO2 flux as influenced by agroecosystem drivers (e.g. soil, topography, micro-climate, organisms, management). Sub-objective 3.b. Determine biogeochemical dynamics of soil C and N including N2O flux as influenced by agroecosystem drivers (e.g. soil, topography, micro-climate, organisms, management). Objective 4. Develop agricultural PM10/PM2.5 and GHG mitigation strategies and management decision aids for Pacific Northwest cropping systems. Sub-objective 4.a. Determine the effectiveness of alternative tillage and cropping practices in reducing the emission of windblown dust and PM10/PM2.5 from agricultural soils. Sub-objective 4.b. Develop precision N management practices that increase N use efficiency and decrease N2O emissions.
1b. Approach (from AD-416):
1a. Sediment and PM10/PM2.5 flux, will be evaluated as a function of soil water content/matric potential & crust type/cover/thickness for five major soil types using a portable wind tunnel. Crust type & morphology will be ascertained by microscopy & PLFA & FAME analyses. 1b. Soil aggregate properties will be assessed under a range of crop & tillage systems being examined to control wind-blown dust. Soil aggregate size classes from different crop & tillage systems will be analyzed to identify microbial community composition (PLFA & FAME analyses), active SOM, C source & crushing strength. 1c. Long-term cropping system studies at Lind, Pullman, & Ritzville will be used to assess impacts on soil quality over time including bulk density, soil pH, electrical conductivity, organic C & N, aggregate size distribution, N movement & soil microbial constituents. 2a. Ongoing research will fingerprint soils & PM10 material from across the PNW using FAME. 2b. Bacteria & fungi containing natural markers will also be evaluated as tracers that can be retrieved from soils due to their unique traits of antibiotic resistance or strain-specific molecular markers to determine point source soil movement. 2c. The FAME & bacterial tracer studies will be used to aid corroboration of the Columbia Plateau regional dust transport model by: (1) determining if modeled emissions are from given fields or grid areas; & (2) characterizing the mode of transport from given regions. 3a. Studies are part of GRACEnet (Greenhouse Gas Reduction through C sequestration & Carbon Enhancement Network) & REAP (Renewable Energy Assessment Project), established to assess management impacts on greenhouse gas emissions & soil C status. We will assess tillage & crop rotation affects on soil C storage across variable soil & terrain attributes of the WSU Cook Agronomy Farm (CAF). 3b. Two studies will assess management & environmental effects on soil C and N cycling & GHG emissions. The first study (CAF) was previously described in sub-objective 3a. The second study was established in 2001 at the USDA Palouse Conservation Field Station & consists of five different farming systems including no-till, perennial biofuels, organic, & native perennials. These two field studies will be used to assess soil gas (CO2, N2O) flux, N mineralization-immobilization-turnover & soil C accumulation. 4a. A portable wind tunnel will be used to assess differences in windblown sediment & PM10/PM2.5 emissions among tillage & cropping systems established at various locations across the Columbia Plateau. Wind speed profiles will be measured using pitot tubes, sediment catch obtained using an isokinetic vertical slot sampler, & PM10 concentration profiles obtained using DustTrak aerosol samplers. 4b. Field studies at the CAF will evaluate two N management treatments for winter & spring wheat: (1) site-specific N management based on the spatial pattern of input variables; & (2) uniform N management. N use efficiency will be evaluated to monitor cropping system N use, assess N management strategies & identify key areas for improvements. Replacing 5348-11000-005-00D(2/10)
3. Progress Report:
Objective 1: To identify practices that promote soil aggregation and thereby control windblown dust, long-term cropping system studies from three precipitation zones of the Pacific Northwest were sampled by USDA-ARS scientists. Samples were characterized for soil aggregation, microbial community structure, enzyme activity, pH, electrical conductivity and carbon. Greater understanding of management impacts on soil aggregation will aid the development of practices that enhance soil resources by controlling soil erosion and promoting soil carbon (C) sequestration. The long-term sites were also sampled to assess management impacts on soil quality and to further understand soil degradation processes. Objective 2: To predict dust emissions from agricultural lands, USDA-ARS scientists characterized soil microbial communities in soil and particulate matter at locations across the western US. ARS scientists also worked on improving fingerprint methodology by applying micro-organisms to soil as tracers that could provide a powerful tool for understanding dust emission source and fate. Soil containing marked strains of bacteria (tracer organisms) created a unique fingerprint that was identified and traced using microbial analyses. Objective 3: USDA-ARS scientists investigated the effects of topography, micro-climate, crop rotation and tillage management on soil C sequestration and nitrogen (N) cycling. Soil C and N dynamics and greenhouse gas (GHG) emissions were measured in long-term cropping system experiments to improve our assessment of GHG’s from agriculture and develop improved technologies and practices to manage emissions. A 64-chamber study with automated GHG flux measurements was deployed in the field with different N rate and glucose treatments. Objective 4: In cooperation with Washington State University scientists, ARS scientists completed a study to assess particulate (PM10) emissions from irrigated cover crops. PM10 emissions were collected from two sites in spring 2012 where mustard had been sown the previous winter. This study will aid in developing management practices for irrigated soils that suppress dust emissions and improve air quality. In cooperation with Washington State University scientists, ARS scientists initiated a study to assess particulate (PM10) emissions from oilseed crops. PM10 emissions were collected from two sites in autumn 2011 where camelina or safflower were grown in rotation with wheat-fallow. This study will aid in identifying potential environmental impacts from growing oilseed crops in the Columbia Plateau. Field studies at the Cook Agronomy Farm, Pullman and in a field near St. John, Washington were conducted by ARS scientists to evaluate wheat plant density and N fertilizer effects on N Use Efficiency (NUE). Precision N management field studies were initiated at the Wilke Farm near Davenport, Washington. Preliminary results show that NUE can be significantly increased by targeting wheat stand density and N fertilizer rates to specific field locations. Databases are being analyzed to improve plant component relationships needed for models such as Water Erosion Prediction Project.
1. Improving wind erosion models for the Columbia Plateau. Wind erosion models have failed to predict wind erosion of soils in the Columbia Plateau, although substantial loss of soil has occurred during high wind events. In cooperation with Washington State university scientists, ARS scientists from Pullman, Washington, found that wind erosion models failed to simulate erosion because of overestimation of the threshold wind velocity that is required to initiate erosion. In fact, the actual threshold velocity of soils in the region is 40% lower than that specified by the models. Performance of wind erosion models can be improved by accounting for the low threshold velocity of soils in the region.
2. Nitrification is dominant in soil nitrogen (N) cycling processes impacting water quality. Agricultural systems are a leading source of nitrogen in aquatic and atmospheric ecosystems. ARS scientists from Pullman, Washington, used labeled nitrate to identify the dominant nitrogen cycle processes and sources of nitrate leached from a dryland agricultural field. Nitrate discharged from the field is the dominant soil nitrogen observed throughout the 5-year study period. There is no evidence that denitrification was occurring at a large enough scale to influence nitrate discharge. During the winter, nitrate discharge originated from nitrification of fertilizer, and during the summer nitrate discharge originated from mineralized soil organic nitrogen. This study shows that understanding regional and localized hydrology is necessary before dominant nitrogen cycling processes can be accurately determined.
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