Location: Soil, Water & Air Resources Research
2017 Annual Report
Objectives
Objective 1: Assess humic products and cover crops as management options for promoting soil carbon pools, nutrient cycling for crop growth, and increased yield.
Objective 2: Assess the effectiveness of grass buffers, blind inlets, and carbon-based reactive barriers in the form of filter socks for phosphorus management.
Objective 3: Quantitatively characterize soil health and crop productivity responses to carbon input from crop sequences and carbon losses from tillage, crop residue management and harvest.
Approach
To enhance management of soil carbon, laboratory analyses for specific carbohydrates, amino compounds, phenols, and fatty acids will be used to distinguish between labile and recalcitrant fractions of soil organic matter (SOM). Effects of applying humic products and cover crops on short- (e.g., nutrient cycling and soil structure) and long-term (e.g., carbon sequestration) soil changes will be determined. Humic product application will be evaluated as a mitigation strategy for SOM loss due to excessive crop residue removal for bioenergy production. Filter socks filled with wood chips and bark will be evaluated as a means to efficiently catch dissolved and sediment-bound phosphorus moving with runoff water into surface inlets, subsurface drainage systems, and ultimately natural water bodies. Process-level knowledge from laboratory and plot-scale research will enhance development of site-specific subfield management strategies for increasing producer profitability and providing sustainable feedstock supplies at field and landscape scales. Several different crop rotations utilizing corn, soybean, alfalfa, wheat, rye, field pea, and tillage radish will be evaluated with various levels of stover harvest. No-tillage, strip-tillage, and chisel-plow management as well as effects of biochar will be determined. Effects on nutrient cycling, soil carbon stocks, and soil health (using the Soil Management Assessment Framework) will be quantified. Project results will provide critical information needed to elucidate the effects of crop residue management and carbon-based amendments on soil physical and biochemical properties, economic returns, and long-term sustainability of corn-based Midwestern cropping systems.
Progress Report
Objective 1. An improved extraction procedure for soil fatty acids was set up. Its previous use elsewhere enabled the distinction of root-derived fatty acids from shoot-derived fatty acids, in addition to the distinction between microbial versus plant fatty acids that is possible with simpler extraction procedures. Vertical patterns in carbohydrate and phenol marker compounds indicated a less decomposed nature of these compounds at depth, although the amounts of total carbon were very low. These results suggest carbon might be more easily sequestered at depth than in shallower layers, although the difficulty remains of incorporating high carbon amounts to depth. To determine whether humic product use enables avoidance of excessive nitrogen fertilizer application rates, a nitrogen fertilizer response trial was set up having five fertilizer rates in continuous corn and corn-soybean rotations for three field seasons. Humic product use was evaluated again in multiple field sites near Ames, Iowa and in Kansas. The responses of soil physical properties (dry aggregate stability, penetration resistance, water-holding capacity, water infiltration rate, bulk density), to humic product application were evaluated at two longer-term field sites.
Objective 2. The quality of water entering surface inlets was monitored as affected by three alternative inlet designs--blind inlet, filter socks, and grass buffer. Of the three practices, the filter socks, which were amended with alum (an aluminum-based material), were the most effective at reducing dissolved phosphorus (by 41-70%). Blind inlets were more effective than filter socks at reducing total water phosphorus (by 56 vs. 33%, respectively) and sediment (56% vs. 29%, respectively). The grass buffers reduced sediment by 60% and total phosphorus by 46%, but they were the least effective practice for reducing dissolved phosphorus (by 42%). The interim results of this research were presented at a farmer-oriented field day, and a brochure highlighting the findings was produced in collaboration with the citizen-led group the Southfork Watershed Alliance. Additionally, the results were presented to the Iowa Secretary of Agriculture in December 2016 and to the Iowa State Soil Conservation Committee in March 2017, at their request.
Objective 3: Combining rye cover crops with corn stover harvest may increase sustainable feedstock supplies and maintain soil resources. Two field studies (2008 to 2014 and 2011 to 2016, respectively) with moderate (~50%) and high (~90%) corn stover harvest on 0-2% slopes in central Iowa were conducted. Corn grain yields ranged from 7.55 to 10.80 Mg ha-1 with no treatment by year interaction or reduction in yield due to the rye cover crop. The second study, which included soybean in the rotation and for which the rye cover was harvested as additional feedstock, resulted in corn grain yields, moderate and high stover removal, rye biomass, and soybean grain yields that averaged 9.72, 3.99, 4.98, 4.00, and 2.90 Mg ha-1, respectively. Using Agricultural Marketing Service (AMS) cornstalk bioenergy market prices, stover harvest would net US $11.47, $14.47, and $16.47 Mg-1 for moderate, high, and high + cover crop harvest strategies. Therefore, incorporating cover crops could enhance stover removal feasibility from environmental and economic perspectives in central Iowa.
Accomplishments
1. Crop, tillage, and landscape position influence soil quality indices in Indiana. The Soil Management Assessment Framework (SMAF) developed by ARS scientists in Ames, Iowa, was used with 10 potential soil quality indicators to assess inherent and dynamic soil and environmental characteristics across crop rotations, tillage practices, and four landscape positions (depressions, toe slopes, side slopes, and summits). Surface physical, chemical, and nutrient component indices were high, averaging 90, 93, and 98% of the optimum, respectively. Surface biology had the lowest component score, averaging 69% of the optimum. Toe-slopes had higher physical, biological, and overall Soil Quality Index values than did summit positions but toe-slope values were not significantly different from those of mid-slope positions. The crop grown prior to sampling had a greater impact on soil quality indicators than did tillage, with perennial grass sites having higher values than either corn or soybean sites. Presumably this reflected greater carbon input through plant roots due to longer growing periods each year, and thus helps producers understand why more diverse cropping systems are recommended to enhance soil quality.
2. Historical variety testing data may provide new insights for improved crop varieties. Variety testing by United States agricultural universities, often in cooperation with experiment stations, and professional crop associations, is recognized as an independent and unbiased validation of the viability of commercial crop varieties, but many of the research records are difficult to locate. A summary report written by an Ames, Iowa ARS scientist and an Iowa State University librarian shows how historical variety testing data can be located and used to help guide new research efforts by crop scientists and agronomists striving to develop new varietal resources for biofuels, bio-products, and other traits. Understanding how libraries store historical information provides a new tool for these stakeholders to obtain information that can be used in their plant breeding programs.
3. Lignification of corn stover following humic product application depends on drought severity. Across four years of measurements in two corn fields outside Ames, Iowa, ARS scientists found that plant material became increasingly woody, that is, showed enhanced lignification, following humic product application in droughty growing seasons. Corn, along with some other crops, becomes woodier during drought stress, but application of the humic product significantly enhanced this response under droughty conditions, with lignification increasing by 9 to 28% compared to corn plants receiving no humic product. The degree of lignification depended on the drought level: lignification increased with humic product application by only about 5% in the year having mild drought stress, no lignification occurred in a year with no drought stress, and increased crop lignification did not occur in lower parts of the fields having more access to water. These results are consistent with the recent hypothesis that humic products promote crop economic yield primarily by strengthening crop tolerance of environmental stresses. This information provides product users with evidence that humic products can help maintain corn growth during droughty conditions.
Review Publications
Pellack, L.J., Karlen, D.L. 2017. Iowa crop variety yield testing: A history and annotated bibliography. Crop Science. 57(4):1984-1998. doi: 10.2135/cropsci2017.01.0009.
Karlen, D.L., Goeser, N., Veum, K.S., Yost, M.A. 2017. On-farm soil health evaluations: Challenges and opportunities. Journal of Soil and Water Conservation Society. 72(2):26A-31A. doi: 10.2489/jswc.72.2.26A.
