Location: Soil, Water & Air Resources Research
2018 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: Soil samples were extracted to recover two size classes of particulate organic matter and the mobile humic acid fraction from the Boyd 21 field and two other field trials of humic product application near Ames, Iowa. The same three fractions of soil organic matter were extracted from soil samples of a cover crop field at three crop growth stages, and the activities of relevant enzymes were also measured at the same times. Rice soil samples from a previous field trial in Arkansas were analyzed by a less harsh analysis for lignin phenols to complement earlier results by our primary method of cupric oxide oxidation. Results confirmed the gradual accumulation of phenols under continuous rice cropping over three years but failed to indicate any capability of soil aeration during the rice growing season to degrade the phenols. Humic product use was evaluated again in multiple field trials near Ames, Iowa. Plant samples were collected for several advanced physiological and biochemical measurements. Initial evaluation of plant hormone concentration data from the 2016 season suggests a causal mechanism for plant growth responses to humic products. Plant samples from 2017 and commercial humic products are being analyzed to further evaluate the proposed explanation.
Objective 2: The quality of water entering surface inlets was monitored as affected by three alternative inlet designs - blind inlets, filter socks, and grass buffers. The results of this research were presented at a farmer-oriented field day in collaboration with the citizen-led group the Southfork Watershed Alliance. Attendees at the field day participated in and observed the installation of a blind inlet and filter socks. In addition, a field study was initiated to compare the capacities of filter socks amended with either woodchips or biochar to reduce losses of herbicides and nutrients transmitted to subsurface drains via surface inlets. Responsibility for this experiment was transferred to the USDA-ARS Laboratory in Oxford, Mississippi upon retirement of the incumbent in June 2018.
Objective 3: Two cropping system studies with tillage, crop rotation, biochar, and crop residue harvest treatments, with 10- and 5-year historical records, contributed to the database of the Rural Energy for America Program (REAP). Systems being evaluated in Study 1 include: (1) chisel-plow and no-till production of continuous corn with no, moderate or high stover removal; (2) an oat/alfalfa – alfalfa–alfalfa–corn–corn rotation with corn stover harvest; (3) continuous corn with legacy biochar treatments and no, moderate, or high stover harvest rates; and (4) a corn–winter rye–soybean-winter wheat–cover crop (radish, pea, and oat) rotation where corn stover, vegetative rye, wheat straw and cover crop vegetation are harvested as potential animal feed or cellulosic feedstock sources. Study 2 focuses on a corn and soybean rotation using strip-tillage with no, moderate, or high-stover removal treatments. Surface (0 to 5- and 5 to 15-cm) and deep core (0 to 120-cm) soil samples were collected in fall 2017 to continue long-term monitoring of a suite of soil health (SH) indicators. Samples are in various stages of analysis, but when completed the entire dataset will be analyzed evaluated using the Soil Management Assessment Framework. Preliminary results for this central Iowa site indicate diversified rotations can reduce N fertilizer requirements and improve several SH indicators. A 10-year assessment of tillage and stover harvest practices within System 1 showed equivalent returns on investment for both tillage practices. Using no-tillage and harvesting an average of 1.5 tons/ac (3.4 Mg/ha) of stover per year corn grain yields averaged 9.5 Mg/ha. Feedstock for bioenergy could be provided at a sustainable rate and soil resources were protected from wind and water erosion.
Accomplishments
1. Plant residues contribute significantly to soil organic matter formation. Soil organic matter plays multiple key roles in soil health and functions, yet its mode of formation remains hotly debated. Recent publications have argued that soil organic matter is composed mostly of microbial cell residues. Hence its accumulation would necessitate accelerated microbial activity in soil, presumably through addition of easily decomposable plant materials. ARS researchers at Ames, Iowa, in coordination with researchers at Iowa State University, demonstrated the direct incorporation of plant carbohydrates into soil organic matter. This incorporation was more efficient with addition to soil of less easily decomposed plant materials—corn and soybean residues--as opposed to the more decomposable alfalfa and oats. These results contradict recent claims that soil organic matter is formed mostly due to microbial processes. They indicate that management of crop residues can directly affect the accumulation of soil organic matter and will guide producers in optimizing levels of soil organic matter.
2. Global standardization is recommended for sampling and analyzing soil carbon. Soil organic carbon (SOC) change influences life-cycle assessment calculations for globally traded bio-based products. A review of SOC sampling and measurements in the U.S. and Brazil showed great variability in sampling techniques (pits versus core samples), sampling depth and increments used for SOC analysis, and analytical procedures (wet oxidation versus dry combustion). To improve consistency and comparability in future SOC studies, ARS researchers in Ames, Iowa, recommend that: (a) the methods applied for each step in SOC studies be documented; (b) a defined protocol for soil pits or coring be applied; (c) samples be analyzed at 10-cm intervals for the full rooting depth and at 20-cm intervals below rooting until reaching 100-cm; (d) stratified sampling schemes be applied where possible to reflect variability across study sites; (e) standard laboratory techniques be used to differentiate among labile and stable SOC fractions; and (f) more long-term approaches be used to assess SOC change. Implementation of these recommendations would enable more consistent life-cycle assessments of bio-based products.
3. What factors influence farmer decisions regarding crop residue management? Corn stover has many potential uses, including harvest as a feedstock for bioenergy or bio-products, or remaining in the field to conserve water, maintain soil organic carbon (organic matter), and protect against soil erosion. Investors in biorefineries and soil conservationists need science-based guidance to help them make appropriate site-specific decisions. ARS researchers in Ames, Iowa, used farm operation, technology, and management variables from the USDA--National Agricultural Statistics Service (NASS) 2010 Agricultural Resource Management Survey (ARMS) report of U.S. corn growers to compare producers who did and did not harvest corn stover. Factors increasing the probability for stover harvest included producing feed corn, managing crop residues for pest control, and farmland ownership. It was well-recognized that excessive stover removal can increase soil degradation by depleting soil organic matter and failing to protect the soil surface from accelerated wind and water erosion. However, the NASS data showed that both groups (stover harvesters and non-harvesters) chose to implement erosion control practices at a rate of 10% or less. Furthermore, because there were very few corn stover markets when the 2010 data were collected, there were more disincentives than positive reasons for harvesting stover. This type of USDA-NASS and -ARS collaboration will be very beneficial to the Department of Energy (DOE) as well as private sector bioenergy and bio-product industries seeking economically, environmentally, and socially sustainable supplies of cellulosic feedstock.
Review Publications
Olk, D.C., Dinnes, D.L., Scoresby, R., Callaway, C.R., Darlington, J.W. 2018. Humic products in agriculture: Potential benefits and research challenges-a review. Journal of Soils and Sediments. 18:2881-2891. https://doi.org/10.1007/s11368-018-1916-4.
Li, Z., Zhao, B., Olk, D.C., Jia, Z., Mao, J., Cai, Y., Zhang, J. 2018. Contributions of residue-C and -N to plant growth and soil organic matter pools under planted and unplanted conditions. Soil Biology and Biochemistry. 120:91-104. https://doi.org/10.1016/j.soilbio.2018.02.005.
Xu, J., Zhao, B., Chu, W., Mao, J., Olk, D.C., Xin, X., Zhang, J. 2017. Altered humin compositions under organic and inorganic fertilization on an intensively cultivated sandy loam soil. Science of the Total Environment. 601-602:356-364. https://doi.org/10.1016/j.scitotenv.2017.05.205.
Korucu, T., Shipitalo, M.J., Kaspar, T.C. 2018. Rye cover crop increases earthworm populations and reduces losses of broadcast, fall-applied, fertilizers in surface runoff. Soil & Tillage Research. 180:99-106. https://doi.org/10.1016/j.still.2018.03.004.
Obrycki, J.F., Karlen, D.L. 2018. Is corn stover harvest predictable using farm operation, technology, and management variables? Agronomy Journal. 110:749–757. https://doi.org/10.2134/agronj2017.08.0504.
Malone, R.W., Obrycki, J., Karlen, D.L., Ma, L., Kaspar, T.C., Jaynes, D.B., Parkin, T.B., Lence, S., Feyereisen, G.W., Fang, Q., Richards, T.L., Gillette, K.L. 2018. Harvesting fertilized rye cover crop: simulated revenue, net energy, and drainage Nitrogen loss. Agricultural and Environmental Letters. 3:170041. https://doi.org/10.2134/ael2017.11.0041.
Li, X., McCarty, G.W., Karlen, D.L., Cambardella, C.A. 2018. Topographic metric predictions of soil organic carbon in Iowa fields. Catena. 160:222-232. https://doi.org/10.1016/j.catena.2017.09.026.
Ippolito, J.A., Bjorneberg, D.L., Stott, D.E., Karlen, D.L. 2018. Soil quality improvement through conversion to sprinkler irrigation. Soil Science Society of America Journal. 81:1505-1516.
Nash, P.R., Gollany, H.T., Novak, J.M., Bauer, P.J., Hunt, P.G., Karlen, D.L. 2018. Simulated soil organic carbon response to tillage, yield, and climate change in the southeastern Coastal Plains. Journal of Environmental Quality. 47:663-673. https://doi.org/10.2134/jeq2017.05.0190.
Cordova, S.C., Olk, D.C., Dietzel, R., Mueller, K., Archontouilis, S., Castellano, M. 2018. Plant litter quality affects the accumulation rate, composition, and stability of mineral-associated soil organic matter. Soil Biology and Biochemistry. 125:115-124. https://doi.org/10.1016/j.soilbio.2018.07.010.
Poffenbarger, H.J., Sawyer, J.E., Barker, D., Olk, D.C., Six, J., Castellano, M.J. 2018. Legacy effects of long-term nitrogen fertilizer application on the fate of nitrogen fertilizer inputs in continuous maize. Agriculture Ecosystems and the Environment. 265:544-555. https://doi.org/10.1016/j.agee.2018.07.005.
Zhang, Y., Yao, S., Cao, X., Schmidt-Rohr, K., Olk, D.C., Mao, J., Zhang, B. 2018. Structural evidence for soil organic matter turnover following glucose addition and microbial controls over soil carbon change at different horizons of a Mollisol. Soil Biology and Biochemistry. 119:63-73. https://doi.org/10.1016/j.soilbio.2018.01.009.
Zhang, Y., Li, L., Mao, J., Yao, S., Schmidt-Rohr, K., Olk, D.C., Cao, X., Cui, J., Zhang, B. 2018. Distinct changes in composition of soil organic matter with length of cropping time in subsoils of a Phaeozem and Chernozem. European Journal of Soil Science. https://onlinelibrary.wiley.com/doi/pdf/10.1111/ejss.12688.
Cherubin, M.R., Souza, T.P., Karlen, D.L. 2017. Healthy soils healthy people: Unraveling the complexity. In: Monteiro, I., Iguti, A.M. editors. Work, Health and Sustainability: An Interdisciplinary International Dialogue South – North. Campinas, Brazil: UnicampBFCM. p. 187-192.
