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United States Department of Agriculture

Agricultural Research Service

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Research Project: Improved Soil Managment Practices for Tilled Summer Fallow in the Pacific Northwest

Location: Soil and Water Conservation Research

2012 Annual Report

1a. Objectives (from AD-416):
1.)Apply new findings on erosion-resistant and water-use-efficient tillage techniques for summer fallow regions of the Pacific Northwest and develop prescriptions for efficient tillage timing.1a.) Measure the performance of coarse summer fallow mulches in on-farm tests, get feedback from farmers, and recommend best tillage practices. 1b.) Identify the optimal timing for creation of a reduced-tillage fallow mulch in the lower precipitation (<350 mm) winter wheat-fallow region and determine if it can be predicted using soil water, temperature, or weather forecasts, and if it is different from the timing farmers already use. 1c.) Predict where early seeding is not necessary from maps of growing degree days following fall precipitation. 2.)Identify dryland cropping systems in the Pacific Northwest capable of maximizing C sequestration and greenhouse gas (GHG) mitigation. 2a.) Identify dryland cropping systems in the Pacific Northwest capable of maximizing carbon sequestration and greenhouse gas mitigation through measurement of soil organic carbon changes and N_2O and CH_4 fluxes in long-term experiments. 2b.) Make projections of CO_2 emissions and soil organic carbon after changes in tillage and cropping system utilizing the CQESTR model.

1b. Approach (from AD-416):
1a.) Soil mulch types from coarse to fine will be compared for their ability to preserve stored soil water. These comparisons will take place for at least three years in small plot experiments in three experiment stations, and in three farmers’ fields in on-farm tests. 1b.) Untilled fallow soil will be continuously monitored during the late winter and spring using electronic moisture and temperature probes. Small plots tilled at intervals over spring and early summer will be measured for stored soil water to determine if moisture and temperature probes plus historic weather data is enough to predict optimal tillage timing. 1c.) Data comparing the difference in yield between early and late emerging winter wheat in different years at many locations will be compiled to see if it correlates with growing degree days available for the development of late-emerging wheat. 2a.) Pacific Northwest cropping systems will be examined in intermediate precipitation zone (425 mm) experiments. Gas samples (CO_2, N_2O, and CH_4) will be collected from selected treatments for three years. Total C, N, and S, extractable P and K, labile C and N fractions, pH, EC, bulk density and wet aggregate stability will be determined. 2b.) The CQESTR model will be used to make predictions of soil organic carbon change and CO_2 emissions and assess the impact of management practices on soil organic matter in reduced tillage fallow and other dryland cropping systems.

3. Progress Report:
An experiment was set up to evaluate the accuracy of two types of probes used for soil water measurement. Manufacturers of these probes typically conduct quality control/quality assurance tests in containers using uniform glass beads and water and assume the resulting measurements for accuracy and precision will be representative of field soils. We tested this assumption by uniformly packing a local soil in containers and then making measurements over a range of known soil water contents and temperatures. We are now analyzing the results from these tests. In March, we installed instrumentation for continuous measurement of soil water content near Pendleton and Moro, Oregon and Lind, Washington. Information collected from these sites will be the basis for establishing optimal timing for primary tillage in summer fallow–winter wheat production. Tillage plots at the three sites were also established. A progression of six tillage timings in replicated plots are in place. Spring weather this year has delivered greater precipitation than normal, so the timing treatments are being extended into late July. At the research station at Pendleton, we are also using 12-inch diameter soil columns set into the ground that can be weighed periodically to measure evaporation from 20 different soil surface conditions. Soil samples were collected from long-term plots at Pendleton and soil analysis is under way. Frequent, year-round greenhouse gas samples have been collected to measure N_2O (nitrogen dioxide), CO_2 (carbon dioxide), and CH_4 (methane) emissions. Grain and biomass yield will be determined at harvest.

4. Accomplishments

Last Modified: 10/15/2017
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