The soil chemistry program is focused on interactions between soil, water, plant and atmosphere. The overall goal of this program is to improve our understanding of biogeochemical processes and anthropogenic environmental changes.
Our main objectives are: 1) assess impacts of farming practices on carbon (C) and nitrogen (N) cycling in agricultural systems, and 2) develop management practices to improve soil C accretion and soil structure, and reduce plant nutrient losses.
The research leads to advanced concepts of organic C and N transformation, C sequestration in soil aggregates, and their effect on surface soil physical properties. Results are expected to produce a series of modifications and additions to the knowledge of C and N dynamics in dryland cropping systems and improve models predicting biological processes within farm fields nationwide.
Greenhouse gas emissions are monitored year-round in the GRACEnet plots
Collecting samples of the soil atmosphere
This project is a cross-location project that includes 32 ARS sites across the USA.
The objectives of this project are: 1) evaluate soil carbon status and direction of change of soil carbon stocks in existing typical and alternative farming systems, and 2) determine net greenhouse gas emissions (CO2, CH4 and N2O) of current agricultural systems including typical and alternative agricultural systems.
Back in the lab, samples are analyzed with Gas Chromatograph
Our approach involves field-scale measurements of soil carbon and greenhouse gases using vented static chambers in conventional winter wheat-summer fallow rotation and other management practices (Continuous winter wheat, and winter wheat-winter wheat-sudan grass rotation with direct seeding) intended to alter greenhouse gas emission.
Soil carbon (C) models are important tools for examining complex interactions between climate, crop and soil management practices, and to evaluate the long-term effects of management practices on C-storage potential in soils. The CQESTR model was developed to evaluate changes in soil organic matter (SOM) at the field scale, and calibrated initially in the Pacific Northwest. We have modified and calibrated the model for national use. A major modification was to quantify soil texture and drainage effects using calibration datasets with a wide range of soil properties.Secondly, the terminating point for organic residue decomposition and residue-to-SOM transfer was changed from calendar-based time to thermal time.A third modification of CQESTR was to separate the surface residue into two compartments, each with a different water coefficient, this was based on the non-uniform decomposition of accumulated surface residue in a no-tillage cropping system as a result of annual residue layering.
A fourth modification involved the inclusion of partially decomposed residue with stable simulated SOM when comparing with SOM observations, since SOM determination unavoidably includes some partially decomposed residue. Finally, a soil organic carbon capacity algorithm was added to account for carbon saturation in some soils due to changes in management practices. The current version of the CQESTR model (v. 2.0) was validated with SOM databases from various regions of North and South America and Africa.
Straw harvest for bioenergy production
This is a multi-unit, cross-location (CLEAR) project. The objectives of this project are: 1) determine the amount of crop residue that must remain on the land to sustain production and maintain soil organic carbon, and 2) develop algorithms to guide the amount of crop residue that can be sustainably harvested for biomass and bio-based products without degrading the soil resource, environmental quality, or productivity.
Our approach involves using measurements taken in plots with residue either removed or returned at different rates from other ARS REAP sites, and applying the CQESTR model to predict how much crop residue can be sustainably harvested while maintaining soil organic carbon.
Carbon source quality influence on soil properties
This research will provide a process-based understanding of how the quality of different organic sources and the plant affect soil chemical, biological and physical properties. The objectives are: 1) evaluate soil carbon status and direction of change of soil carbon content in the presence of source carbon materials, and 2) determine if quality of organic material entering the soil is more important than the quantity of organic matter in stabilizing soil aggregates.
Our approach involves establishing a small plot experiment with two main treatments (continuous winter wheat, and continuous fallow) and a variety of carbon sources having specific chemical properties applied annually to the surface soil of individual plots for five years. Treatments included wood (lignin), wheat straw, sucrose, cotton (cellulose), alfalfa pellets (high amino N), manure, municipal biosolids (humic substance), composted wheat residue, perennial grass, winter brassica residue, winter brassica crops, and a check (no addition). Temporal dynamics of soil organic carbon and soil aggregates and their stability are determined, and their correlation to different C sources will be developed.