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Research Project: Attaining High Quality Soft White Winter Wheat through Optimal Management of Nitrogen, Residue and Soil Microbes

Location: Columbia Plateau Conservation Research Center

2020 Annual Report

Obj. 1: Extend the N replacement approach to soft white winter wheat for guiding precision management of fertilizer N and crop residue to optimize soil microbial processes and maximize the biological potential of soil. 1A: Evaluate grain protein concentration and yield response to N under varying levels of water to define the critical protein level and fertilizer N equivalent to a unit change in protein for popular cultivars of soft white winter wheat. 1B: Determine whether uniformity of protein levels in the crop can be achieved with the precision N replacement approach. 1C: Adapt instruments and algorithms to support on-farm implementation of the N replacement approach to precision fertilizer management in dryland wheat production systems. 1D: Evaluate the effects of residue management (standing, distributed on the soil surface, or removed) on the plant-available N, precipitation capture efficiency, crop productivity, weed density, and microbial activity during the 13 months of fallow. Obj. 2: Identify whether soil microbial communities adapted to dry environments benefit plant fitness under water limited conditions. 2A: Identify the composition of microbial consortia naturally adapted to low water availability. 2B: Determine whether cultivar selection and N management can be manipulated to shift the structure and function of microbial communities to benefit plants under water stress. Obj. 3. Develop resilient cropping systems and strategies that increase resilience, improve economic returns, and enhance ecosystem services; assess their economic and environmental performance of various cropping systems in concert with their supporting components; and develop decision support systems for optimizing agronomic production in these cropping systems. 3A: Compare economic returns from the variable N replacement approach based on previous season’s site-specific SWW crop yield data and conventional uniform N placement based on field bulk soil sampling and laboratory testing. 3B: Increase dryland farming resilience by developing cropping systems more intensive and diverse than the conventional winter wheat-fallow system. 3C: Investigate the yields and economic returns of alternative crops following winter wheat and winter wheat following cover crops across low and intermediate precipitation zones using current and future climate scenarios. Obj. 4. Increase the sustainability resilience and tolerance of the dryland crop production system to biotic and abiotic stressors through improved understanding of developmental, environmental, and management factors that limit plant health and growth, including but not limited to stress tolerance, water use efficiency, and disease resistance. 4A: Evaluate stress indicators and yield components of wheat in alternative cropping systems compared to wheat-fallow with relation to soil water availability, disease incidence, and rotational crop morphology. 4B: Investigate crop response to water deficit, high temperature, and/or nitrogen availability.

1A: A winter wheat-fallow Cultivar-Fertility Study located at 2 sites in the low and intermediate precipitation zone in Eastern Oregon will include 3 soft white winter wheat cultivars fertilized with inorganic nitrogen (N) at 4 rates. The study will be repeated for 3 years. Yield and grain protein concentration (GPC) measured with near-infrared spectroscopy will define the critical GPC, an indicator of crop N deficiency or adequacy. 1B: A N-Replacement Study will follow 1A in which plots will be split and fertilized based on 1) amount of N needed to achieve target protein based on the critical GPC, and 2) university recommendations based on soil N and potential yield. Select plots will be analyzed for inorganic N, nutrient cycling capacity, microbial community composition, N leaching and gaseous N loss. 1C: The GPC measurements from the relatively inexpensive AvaSpec2048 spectrophotometer will be compared to data from dry combustion. Publicly available software will be adapted from Yield Editor software in collaboration with ARS, Columbia Missouri. 1D: Winter wheat residue in the 2 precipitation zones 1) cut high, left standing, 2) cut high, flattened, 3) cut low, spread, 4) cut low, removed. Measurements include yield, soil/air temperature, air movement, soil water content, inorganic N, and microbial nutrient-cycling activity. 2A: Rhizosphere and bulk soil microbial communities will be characterized from plots replicated in the low and intermediate precipitation zones. Soils will be analyzed for chemistry and enzymes related to carbon and N-cycling, and microbial composition. 2B: Rhizosphere soils collected from different cultivars of 1A at 2 N rates will be analyzed for nutrient cycling activity and communities sequenced from treatments promoting or inhibiting activity. Microbial communities will be evaluated for benefit to wheat in a microbial transfer potting experiment. 3: Economic benefit from replacement N management and intensified cropping systems will be evaluated. An alternative crop trial (AC) and cover crop trial (CC) will be conducted. The winter wheat (WW)-chemical fallow (CF) system will be intensified in a low precipitation (<250 mm) site as a WW-AC-CF rotation and at a high precipitation (<420-mm) site as a WW-AC rotation. The CC trial will be conducted at both sites as WW-cover crop fallow. Each trial will be initiated at a new location for three replicate years. A calibrated model will be provided within a crop simulation platform that will be useful for determining the different alternative crops and cover crops that producers are likely to consider. 4: The plant stress response and yield differences will be evaluated in the alternative and cover crop trials. Soil water availability, disease incidence, soil nutrient cycling, soil chemistry and yield traits will be quantified in each of the trials. Multiple regressions will be used to model the yield and stress variables as a function of the abiotic stressors. Results will identify benefits or detriments of alternative cropping systems to the primary wheat crop in terms of herbicide use, disease incidence, nutrient availability, soil quality, and water availability.

Progress Report
In support of Sub-objective 1A, we made significant progress toward determining the critical protein level in soft white winter wheat below which yield is impacted by insufficient nitrogen nutrition. Suitable land was found for a field experiment with four wheat cultivars grown in combination with five nitrogen fertility regimes. Experiments were established fall 2019 at high rainfall and low rainfall sites in eastern Oregon. Under Sub-objective 1B, we made significant progress toward determining how fertilizer application impacts microbial activity associated with the soil’s ability to supply nitrogen. Fertility tests, including micronutrients, were performed at both sites for baseline values. Analysis of the soil microbial ammonia oxidation activity, the first step in nitrification, was completed for all cultivars at both sites in plots that were unfertilized or that received the two highest nitrogen application rates. Substantial progress was made under Sub-objective 1B3 in determining fertilizer use efficiency with attention to nitrogen losses due to volatilization and leaching. A three-year database was compiled that includes measured plot observations of grain yield, grain protein concentration, harvest index, nitrous oxide, and ammonia. Nitrate movement below the root zone was monitored in deep soil cores at the start and end of each growing season. The research supporting Sub-objective 1C1 is now complete, which involved evaluating the field precision of a relatively inexpensive spectrometer for protein analysis of wheat. An instrument costing less than $6,000 was successfully adapted for use on a combine harvester. Agricultural producers and instrument manufacturers have new information on which to modify affordable spectrometers for on-combine use, including precision nitrogen management, grain segregation/blending, and late-season weed mapping. Under Sub-objective 1C2, we made significant progress in developing and testing a grain yield/protein mapping software. The software will assist growers interested in tools for developing grain yield and protein maps to create fertilizer application plans. Under Sub-objective 1D, we made significant progress in planting a residue management trial and acquiring the farm equipment for creating residue management treatments. Wind speed, temperature, and humidity sensors were prepared for deployment in fall 2020. A relatively low-cost method for measuring in-field soil respiration was developed using an indicator that responds to carbon dioxide levels with a simple color change from pink to yellow. Significant progress was made under Sub-objective 2B in optimizing protocols for microbial community sequencing of full-length ribosomal DNA. Also, progress was made in developing a high throughput microplate method to quantify urease activity. Progress on Objectives 3 and 4 have been made in a first-year trial for the fall-seeded alternative crops. Two cropping studies, an alternative crop trial, and a cover crop trial were initiated in the low and intermediate precipitation regions by Oregon State University through a Non-Assistance Cooperative Agreement. Data were collected for emergence, soil moisture, and ground cover as a measure of weed competitiveness. Commercial fall-seeded legumes and two winter pea varieties from the Pullman ARS breeding program are showing positive results for emergence and weed competition at the two sites.

1. Mapping grain protein concentration on-combine with a moderately-priced spectrometer. The ability to map grain protein concentration on-combine is unachievable to many farmers based on the high cost (more than $20,000) of the commercially-available spectrometer. ARS scientists in Pendleton, Oregon, adapted a moderately-priced reflectance spectrometer (less than $5,500) for use on a combine to measure and map the protein concentration of wheat during harvest. When placed on a combine, the calibrated instrument produced a protein map that compared well with a map derived from a more expensive instrument ($32,000). A less costly instrument may be adapted for mapping protein across fields, thereby helping promote the adoption of sensing technology for use by farmers in precision nitrogen management, grain segregation/blending, and post-harvest weed mapping.

2. Reduced sensitivity of septoria tritici blotch pathogen to SDHI fungicides following their regional adoption. Zymoseptoria (Z.) tritici, the causal agent of septoria tritici blotch disease in wheat, results in significant yield loss worldwide. Z. tritici life cycle, reproductive system, abundance, and gene flow put it at a high likelihood of developing fungicide resistance. Oregon State University and ARS researchers in Pendleton, Oregon, evaluated the sensitivity of Z. tritici isolates to four fungicides in the succinate dehydrogenase inhibitor (SDHI) group of fungicides. Z. tritici isolates were collected from fields in the Willamette Valley of Oregon at dates spanning the introduction of SDHI to the region. The sensitivity of Z. tritici to benzovindiflupyr, an active ingredient of SDHI, decreased following the fungicides' introduction to the region, and cross-sensitivity was observed with pethiopyrad, another SDHI. The results demonstrate that careful consideration is required to manage fungicide resistance and suggests that between-group, rather than within-group fungicide rotation, is necessary to prolong SDHI efficacy.

3. The wheat-fallow rotation can be intensified with spring crops under low annual precipitation. The ability to intensify the traditional winter wheat-fallow rotation in dryland cropping systems can be limited by the lack of plant-available water to support yield. ARS scientists and an Oregon State University colleague in Pendleton, Oregon, evaluated the productivity and soil water use of two-year (winter wheat-fallow) and three-year crop sequences in the Pacific Northwest (PNW) receiving approximately 11 inches of annual precipitation. Water infiltration was significantly greater in the winter wheat-fallow rotation with minimum tillage, rather than wheat-fallow with intensified tillage or three-year rotations with spring barley or spring oilseed. The greatest annualized yields and water use efficiencies were rotations in which winter wheat followed minimum tillage fallow. Rotations of minimum tillage fallow-winter wheat-spring barley or spring oilseed carinata showed the most promise of the three-year intensified rotations in which the water use efficiency and total grain productivity were similar to the two-year fallow-winter wheat rotation. Spring barley and spring carinata can be integrated into three-year dryland rotations with winter wheat under low precipitation dryland conditions in the PNW.

4. Yield maps from multiple years can identify productivity zones for site-specific crop management. Maps of crop productivity can be generated using on-combine yield monitors. ARS scientists at Pendleton, Oregon, examined whether yield maps collected over multiple years could reveal regions in the field with consistently low or high productivity to construct zones for precision agriculture. A specialized mathematical method was applied to several years of yield map data from a dryland field in east-central South Dakota (corn, soybean rotation) and an irrigated field in southwest Georgia (corn, soybean, and peanut). In both the dryland and irrigated systems, the method effectively revealed patterns of productivity in the time-series data, which appeared to be related to changes in soil type and landscape position. Results from this study may benefit farmers who practice site-specific management by identifying areas within fields that are historically more (or less) productive than others.

5. Diversifying the dryland wheat-fallow rotation with oilseeds can increase water infiltration. Rapid water infiltration into soil is important for storing water and reducing erosion. In semi-arid climates, cropping systems may include a fallow, or unplanted period, to accumulate precipitation for the following crop. Wheat production in regions of the Pacific Northwest receiving less than 14 inches of annual precipitation rely heavily on the two-year winter wheat-fallow system; however, when used with tillage, the system can have negative impacts on soil structure, soil quality, and erodibility. ARS scientists and Oregon State University colleagues in Pendleton, Oregon, evaluated whether intensification of the wheat-fallow system with canola or mustard oilseed crops would increase water infiltration based on the differences in the fibrous branching wheat roots vs. oilseed taproots. The three-year study demonstrated that water infiltration rates were increased by oilseeds compared to wheat; however, the increase in infiltration did not confer a yield benefit to the following wheat crop. This knowledge guides growers in selecting rotational crops.

Review Publications
Williams, J.D., Reardon, C.L., Long, D.S. 2020. Productivity and water use efficiency of intensified dryland cropping systems under low precipitation in Pacific Northwest, USA. Field Crops Research. 254.
Hagerty, C.H., Klein, A.M., Reardon, C.L., Kroese, D.R., Graber, K.R., Melle, C.J., Mundt, C.C. 2020. Baseline and temporal changes in sensitivity of Zymoseptoria tritici isolates to benzovindiflupyr in Oregon, USA, and cross-sensitivity to other SDHI fungicides. Plant Disease. Available:
Long, D.S., McCallum, J.D. 2020. Adapting a relatively low-cost reflectance spectrometer for on-combine sensing of grain protein concentration. Computers and Electronics in Agriculture. 174.