Project 1: IMPACTS OF GRASSLAND REESTABLISHMENT VIA CONSERVATION RESERVE PROGRAM ON SOIL HEALTH
Grassland reestablishment under the Conservation Reserve Program (CRP) is a U.S. federal land conservation program, provides many ecological benefits such as preservation and restoration of forests and wetlands, wildlife habitat, improved air and water quality, and carbon sequestration. Despite these benefits, two critical questions remain: does reestablishing grasslands via CRP also result in soil health recovery, and what parts of restored fields (i.e. topographic positions) recover the fastest? We hypothesized that soil health will recover over time after converting cropland to CRP grassland, and recovery will be greatest at higher topographic positions. To test this, we sampled Midwest U.S. soils along a grassland chronosequence (0–40 y, including native grasslands) and at four topographic positions (shoulder-, back-, foot-, and toe- slope). Soils were measured for several physical (bulk density and maximum water holding capacity), chemical (soil organic carbon and extractable inorganic nitrogen), and biological indicators (potentially mineralizable carbon and nitrogen) of soil health and how these indicators vary with time since reestablishment to CRP and across different topographic positions. The results of this project will help the land managers, natural resource managers, and policymakers to understand the potential soil and environmental health benefits of CRP in order to take sustainable management decisions.
ORAL PRESENTATION: Impact of conservation reserve program on soil health.
Published Journal Article: De, M., J.A. Riopel, L.J. Cihacek, M. Lawrinenko, R. Baldwin-Kordick, S.J. Hall, and M.D. McDaniel. 2019. Soil health recovery after grassland reestablishment on cropland – the effects of time and topographic position. Soil Sci. Soc. Am. J. 84:568–586. https://acsess.onlinelibrary.wiley.com/doi/full/10.1002/saj2.20007
Project 2: CRUDE GLYCERIN AS A SOIL AMENDMENT TO TEMPORARILY STORE AND RESUPPLY NITROGEN TO CROPS
The intensification of annual row crop production in the Midwestern U.S. is linked to nitrate (NO3-) contamination in surface and ground waters; most of this NO3- is lost when soils are bare and there are no growing crops as in the late fall to early spring. Winter cover crops have been successfully used to mitigate much of the NO3- loss during these periods. Unfortunately, cover crops do not work in all scenarios. Hence, we test a natural byproduct of the biodiesel production process, crude glycerin, as a source of carbon (C) and whether adding glycerin to soils increases microbial activity and biomass production, and subsequently reduces NO3-N in soil. A lab-based incubation study was conducted with two different soils – 1) loam with 6% soil organic matter (SOM) and 2) sand with 2% SOM. Soil inorganic N (NH4-N + NO3-N) and microbial biomass C and N were measured at 1, 3, 7, 14, 28, 63, and 100 days after adding 4 glycerin rates (0, 117, 468, and 1872 mg C/kg soil) combined with 3 calcium nitrate rates (0, 10, and 40 ppm N). The CO2 efflux was also measured. The study findings will suggest whether glycerin has the potential to be a soil additive that can temporarily immobilize NO3-N when it is most vulnerable to loss, and then have the N slowly available to the next growing crop.
ORAL PRESENTATION: Glycerin as a soil amendment to temporarily store and resupply nitrogen to crops. Evidence from an incubation study.
Published Journal Article: De, M., J. Sawyer, and M.D. McDaniel. 2022. Crude glycerin, a biodiesel byproduct, as a soil amendment to temporarily immobilize and then release nitrogen. European J. Soil Sci. 73(3): e13241.
Project 3: EUTROPHICATION POTENTIAL OF TILE DRAINAGE WATER ON IOWA STREAMS
Water quality issues related to excess nutrients are one of Iowa's most widespread, costly, and challenging problems. Fertilizer nitrogen (N) and phosphorus are added to agricultural fields to increase yields, but these nutrients also limit algal growth in the aquatic ecosystems and in excess can lead to eutrophication. Tile drainage system is used extensively across the U.S. Midwest to improve yields, but these tile drainage lines can directly transport nutrients to streams - effectively bypassing natural stream buffers. This study was designed to understand the effects of tile water on eutrophication potential of Iowa streams. We hypothesized that streams without a prior history of excess nutrients will be more sensitive to tile water from conventional soil management practices. To test this, tile water from three soil management practices (no cover crop and tillage, cover crop and tillage, and restored prairie) was incubated with stream water from three eutrophication statuses [low- (< 2 ppm NO3-), medium- (~ 5-8 ppm NO3-), and high-impacted (> 10 ppm NO3-)], and at different mixing ratios (5%, 10% and 25% tile:stream water volume). Fourteen days after mixing stream and tile water, we measured chlorophyll-a (chl-a) and dissolved oxygen (DO) as indicators of eutrophication potential. Our study results will indicate how different crop and management practices is directly related to tile water quality to mitigate the agricultural impacts on stream water health.
POSTER PRESENTATION: Linking soil management practices to eutrophication potential in Iowa streams.
Project 4: SOIL BIOLOGY AND NUTRIENT CYCLING IN CONVENTIONAL AND LOW-EXTERNAL-INPUT CROPPING SYSTEMS
Subsurface nutrient losses and soil biology differ between annual and perennial crops; however, nutrient losses and soil biology from cropping systems that include both annual and perennial crops in rotations are poorly understood. A long-term cropping experiment (2002-present) located in Central Iowa where two cropping systems were compared: 1) an inorganically-fertilized, 2-year corn-soybean rotation (conventional system, typical of the U.S. Midwest), and 2) a manure-fertilized, 4-year corn-soy-oat/alfalfa-alfalfa rotation (low external input, LEI system) to understand the differences in nutrient cycling and biological indicators of soil health. We hypothesized that LEI systems will have greater microbial biomass and smaller concentration of nitrate as compared to conventional farming systems. To test this, soil samples were collected from 0-15 and 15-30 cm depths and analyzed for microbial biomass C and N and 2M KCl extractable NH4-N and NO3-N. Soil water samples were collected from 1.2 m depth using suction cup lysimeters and analyzed for different inorganic N fractions. Study results will provide evidence if rotational systems including alfalfa with annual crops and use of fertilizer management can reduce movement of nutrients below the root zone and improve soil biology. Further, our results can be linked with yield, nutrient-cycling efficiency, and soil health to determine which systems would be a sustainable management practice.
Published Journal Article: Baldwin-Kordick, R., M. De, M.D. Lopez, M. Liebman, N. Lauter, J. Marino, and M.D. McDaniel. 2022. Comprehensive impacts of diversified cropping on soil health and sustainability. Agroecol. Sustain. Food Syst. 46(3): 331-363.
Project 5: EFFECTS OF MANAGEMENT HISTORY ON ROOT CHARACTERISTICS AND SOIL HEALTH
Plant roots contribute to the soil organic carbon (SOC) pool as deep as the rooting system occupies. Root C pool size and SOC pool size are often been suggested to have a direct relationship and that SOC plays a central role in maintaining soil health. Yet, little is known about how the changes in management history have an impact in the changes of root C inputs and associated soil health. We examined differences between Conservation Reserve Program (CRP), pasture, and row crop (i.e. corn) root characteristics to a depth of 1.2 m to determine the effect of management history, topographic positions (high vs low slope) and their interactions. We hypothesized that distribution of root C:N in the 1.2 m soil profile would increase with the depth and CRP and pasture roots would contribute more C to the soil than the corn roots. Our study results will be correlated with soil physical, chemical and biological indicators of soil health to design systems that maintain and build soils that are productive and resilient.
Journal Article (IN PREPARATION): Moore, E.B., M. De, V. Gin, J. Johnson, M. Nunes, D. Saha, D. Karlen, and M.D. McDaniel. Land use, but not landscape position, regulates soil-to-plant-root relationships. (Target Journal “European J. Soil Sci”)