Project Number: 5356-11120-003-01
Project Type: Specific Cooperative Agreement

Start Date: Sep 26, 2008
End Date: Aug 31, 2013

Objective:
The objective of this cooperative research project is to investigate soil organic carbon dynamics in the long-term plots at CBARC in Pendleton using a process-based soil carbon (C) model, the CQESTR model. Specifically this project is conducted to: 1) determine soil organic carbon dynamics over 75 years of repeat additions or removal of carbon sources, fertilizer levels, and tillage practices; 2) predict the potential of C accretions or losses with varying crop rotation, tillage, and amendment scenarios.

Approach:
Long-term field experiments (LTE) with repeat additions or removal of carbon sources are ideal to examine soil organic carbon (SOC) dynamics and validate soil C models. CBARC is home to the oldest experiments in the western U.S. with some of the experiments dating back to the 1931. The management and treatments of most of the experiments have changed little since their establishment. Several residue burn treatments had a minor change in 1978. Nitrogen was broadcast as (NH_4)_2SO_4 from 1931 to 1961 and as NH_4NO_3 since 1962. The spring residue burning with no N addition, fall burning with no N addition, manure application at 11.2 t/ha/yr (741 kg C and 56 kg N/ha/yr), pea vine addition at 1.12 t /ha/yr (397 kg C and 17 kg N/ha/yr), or no residue burning with 0, 45, and 90 kg N/ha have all been in place since 1967. These treatments were initiated to diminish or eliminate the detrimental effects of conventional tillage winter wheat-summer fallow system, which is the predominant cropping system in the Pacific Northwest, on SOC. Soil carbon content of these long-term plots is determined every 10 years. The collected SOC data will be used to prepare a database for these fields to elucidate the effect of repeat additions or removal of carbon sources on soil carbon accretion or loss. Soil carbon dynamics during 75 years will be determined. CQESTR, a C balance model developed by ARS scientists at the Columbia Plateau Soil Conservation Research Center (CPCRC) in Pendleton, will be used to predict SOC status at the field-scale. RUSLE files (c-factor files) for LTE plots will be prepared for use with CQESTR. Simulation runs with the CQESTR model will be performed to predict changes in SOC. Simulation results will be compared to the measured SOC. The influence of repeat additions or removal of carbon sources or different C sources on SOC will be determined. Prediction runs with the CQESTR model will be undertaken with varying crop rotation, tillage, and amendment scenarios.