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ARS Home » Pacific West Area » Pullman, Washington » Northwest Sustainable Agroecosystems Research » Research » Research Project #444946

Research Project: Impacts of Long-Term Management on Surface and Subsurface Transport and Biogeochemical Fluxes within the Cook Agronomy Farm

Location: Northwest Sustainable Agroecosystems Research

Project Number: 2090-11000-010-021-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 1, 2023
End Date: Aug 31, 2028

The first objective is to quantify nutrient, base-cation, and sediment loading from both the reduced and no-till paired catchments. We also want to continue monitoring export and the long-term no-tillage drain site document the percentage of the total historic nutrient and base-cation export from the no-tillage field site that was derived specifically to the no-tillage catchment. This will help interpret differences in historic research with the data collection going forward at the new Cook East catchment site. Continue monitoring the smaller Cook west bowl located south of the new reduced till catchment site. This will give us some idea of spatial variability in export and provide baseline measurements for future projects where a unique treatment difference is applied to the southern and northern bowl on the reduced tillage side of the farm (Cook West).

Objective 1A: Quantify base cation export from surface runoff and subsurface drainage from paired No-till and Reduced Till systems. Continue measuring base cation export from Cook Agronomy Farm (CAF). Event based water samples from subsurface and surface sources at Cook East and Cook West field sites as a comparison between management practices. Objective 1B: Phosphate isotope analysis. Pair the nutrient analysis in objectives 1A-1B with a more detailed analysis of P-18O isotope signatures of phosphate in tile-drain water samples. Specifically, more extensively sample subsurface and surface runoff from both tillage management treatments to determine if P-18O are unique and distinguishable. The goal for the next season is collect a larger temporal sequence of the tile drains (i.e., capture the entire water year from fall to summer) and surface run-off. We will also include the analysis of water isotopes (Delta o-18, Delta h-2) from the tile drain and soil water to coincide with the P-18O analysis. We will also explore variability in plant and litter P sources across the field through a trichloroacetic acid/nitric acid extraction. In 2020, alab-based approach was developed to analyze P-18O isotope signatures of phosphate in water samples. We were able to successfully develop this approach and we initiated analysis of subsurface drainage water samples and water extractable soil phosphorus during the spring of 2021. The water extractable soil phosphorus isotopic signature was consistent during the spring until the tile drains began to dry-out, varying by at most one per mil. The tile drain P-18O isotope signatures were close to equilibrium with precipitation Delta o-18 during the early water year. During the late season, the reduced-till tile drain values were far from equilibrium as the precipitation isotopic values changed with different storm systems. With the limited data that we have, we have demonstrated that P-18O is out of equilibrium during the water year and can thus be used to trace different P sources at the CAF. We will continue this analysis to more confidently assess impacts of tillage management on phosphorus export. This analysis provides critical information on the sources and types of P cycling that occurs in these agroecosystems. The information derived from the P-18O signature of different pools will be highly complementary to the phosphorus export measurements in Objective 1a by potentially identifying different legacy phosphorus sources and quantifying P use efficiency. Objective 2A: Nutrient Balance through Crop Measurement and Modeling. Combine water quality loading measurements with on-going crop sampling at each of the pair sites to document overall input, export and storage of major nutrients. Biomass growth from the no-till catchment appears to be consistently higher than the reduced till catchment. We believe this is affecting nutrient removal and ultimately may be a signature of decreased reliance on synthetic fertilizers.