NC1178: Land use and management practice impacts on soil carbon and associated agroecosystems services

(Multistate Research Project)

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Soils play important functions in sustaining crop productivity, maintaining plant, animal and human health, and providing various ecosystem services. However, intensive management practices, land use conversions, and climate impact soils and crop production. Therefore, there is strong need to maintain and improve the soil quality, and increase productivity while minimizing the negative impacts on the environment. Soil organic carbon (SOC) is key to various soil functions. It has been reported that upon conversion from natural to agricultural systems, soils lose 42% of their native C pool (Guo and Gifford, 2002). This can be partially mitigated by practices that enhance sequestering SOC. Enhancement of the SOC pool can be achieved through sequestering of atmospheric CO2; it also reduces net emission of radiatively-active gases (greenhouse gases or GHG) into the atmosphere, and improves the quality of soil and water resources. However, sequestering this C has also been challenged by problems such as intensive soil tillage and associated problems such as soil compaction and soil erosion. This project will focus on improving the soil C through sustainable use of differing conservation practices, for example, no-tillage (NT), organic farming, mixed cover crops, and residue mulch. When crop residue is removed from soil coupled with intensive tillage, there is increased potential for soil erosion, reduction in SOC pools, and deterioration of soil properties, resulting in a subsequent decline in soil quality, reduction in crop yield, and decrease in local and regional water quality (Simpson et al., 2008). Thus, a protective cover or residue mulch under reduced or no tillage practices helps in improving the soil properties and reducing the soil erosion. This project will develop improved management practices including integrating livestock production systems (for example, improved grazing), and determine their influences on soils and environmental quality. 


Crosson (1984) estimated a monetary loss in the U.S. from soil erosion due to reduced cropland productivity to be $40 million in a given year. In 2001, den Biggelaar et al. (2001) estimated the loss at $55.6 million. Others, Crosson (1986) and Pimentel et al. (1995), have estimated the loss to be over $100 million. The results vary depending on the erosion rates, climate, and crop prices for the years covered in the study. For many soils, continued erosion results in degraded and reduced topsoil thickness. Reduced crop yields occur as root restrictive layer, such as fragipan, subsoil horizons with a large amount of clay, or coarse sand become closer to the soil surface (Langdale et al., 1985). Offsite damages to the environment caused by soil erosion and subsequent deposition of sediments in the U.S. are considerable (Pimentel, 1992). Deposition of eroded soil materials in surface water bodies such as reservoirs, lakes, rivers, and streams cause a decline in water quality, reduce environmental quality, and decrease the functional life expectancy of reservoirs. Eroded sediments often contain not only soil materials from the organic surface soil, which are enriched in nutrients and C, but often include commercial and/or organic (animal waste) fertilizers, pesticides, and agricultural pharmaceuticals (from animal waste). Management practices such as cover crops and no-till systems improve SOC, which is one of the critical indicators of development of soil physical, chemical, and biological properties (Blanco-Canqui et al., 2013). If management practices increase SOC, the physical, chemical, and biological properties are positively affected, and vice versa. Many of the soils of the North Central region possess silty surface textures which are naturally more susceptible to physical degradation and reduction in SOC pools. Decline in soil organic C concentration and deterioration of soil structural properties as a result of tillage and land use conversion can be significant. 


Soil is a finite resource. The average soil erosion rate in the United States is 10.3 Mg ha-1 or 0.08 cm of top soil loss annually (National Resources Inventory, 2012). Of this, 6.0 Mg ha-1 is caused by water, 4.3 Mg ha-1 by wind. However, the average annual soil formation rate around the world is only 0.54 Mg ha-1 or 0.004 cm of top soil annually (Alexander, 1998). Thus, managing for soil health has long-term implications for agroecosystem sustainability, productivity, and environmental quality (Karlen et al., 1997). Yet, most farming practices decisions only consider short-term goals based machinery operation, creating an ample seed bed, and application of fertilizers, herbicides, and insecticides to maximize immediate grain or forage yields. These factors in conjunction with varying seasonal temperatures, water availability, and market demand determine which crop to plant, tillage system to use, and the farm’s potential productivity.


The management of soil health is generally overlooked during the farm management planning process. Nonetheless, it is essential in protecting and sustaining long-term soil productivity from destructive and unbalanced management practices such as intensive tillage and excessive application of chemicals that lead to soil and water quality degradation (Doran, 2002; Lal et al., 1998). Soil health refers to self-regulation, resistance, resilience, and lack of stress symptoms (e.g. compaction, low nutrients, lack of biological activity) in a soil as an ecosystem (Weil and Brady, 2016). Self-regulation refers to an ecosystem that can cycle its own nutrients and sustain high productivity with very little external inputs as done for millennia in native (undisturbed) prairies and forest ecosystems. Soil resistance is the capacity of the soil system to continue to function without change throughout a disturbance (Seybold et al., 1999). Soil resilience is the capacity of a soil to recover after disturbance (Seybold et al., 1999). Instances of soil disturbance include, fire, tillage, flooding, drought, and over-grazing.


The key to increasing the soil’s resilience against stressful climate conditions is to build or maintain soil health by improving the physical, chemical and biological properties of soil. Soil physical properties provide the structure in which plant roots and soil organisms live. Healthy soils have granular and aggregated soil structure that allow for water and air to move through the soil and be stored in the soil. Soil aggregates are primarily formed in three ways: i) by polyvalent cations like calcium (Ca2+), magnesium (Mg2+), and aluminum (Al3+) binding together clay particles, ii) fungal hyphae and fine roots stabilizing aggregates, and iii) cementation of soil particles by organic glues created by fungi and bacteria decomposing organic matter, and by exudates from roots (Six et al., 2002). Managing soil physical health requires reducing soil erosion, compaction, tillage intensity, and removal of vegetation while increasing organic matter and soil organisms’ activity. Soil chemical properties ensure the supply of nutrients for plants and soil organisms uptake. Some elements and chemical compounds at adequate quantities are essential for plant growth, such as nitrate (NO3-), ammonium (NH4+), orthophosphate (H2PO4-), potassium (K+), sulfate (SO42-) and Ca2+. Other elements and chemical compounds are not essential and may be toxic at high concentrations, such as aluminum toxicity, salinity, heavy metals, and acidity. Managing soil chemical health requires balancing soil pH (affects the availability of elements), controlling the release of nutrients from organic matter and fertilizers, and avoiding use of chemicals harmful to beneficial soil organisms. Pesticides are used to decimate unwanted pest that cause yield losses, but also have unattended negative consequence on beneficial insects and non-target plants (Desneux et al., 2007). Excessive fertilizer and manure applications can also result in N and P surplus to accumulate in soil, some of which is transported to aquatic ecosystems initiating eutrophication (Carpenter et al., 1998). Soil biological properties encourage active communities of soil organisms essential to healthy soils. Soil microorganisms play key roles in nutrient acquisition (mycorrhizal fungi), N cycling (rhizobia, actinomycetes, free-living bacteria), C cycling (mycorrhizal fungi, bacteria, decomposing fungi) and soil formation (Van Der Heijden et al., 2008). They may also play a role in suppression of disease causing organisms and influencing the degradation of pollutants (Singh et al., 2011). However, more research is needed in linking biological soil health with productivity. For instance, a study in South Dakota has shown that crops grown in a no-till system (higher microbial activities) may be expected to resist low available P as well as other stresses better than crops in conventionally tilled soils (Carpenter-Boggs et al., 2003). Management of soil biological health requires maintaining or increasing soil organic matter (SOM), balancing soil acidity and salinity as well as good soil structure and aeration.


SOM can be used as an overall soil health indicator since it influences the physical, chemical and biological properties of soils. SOM consists of living and decaying plant residues and roots, living and decaying soil biota, and soil humus (stable decomposed organic matter). Managing for SOM to improve soil health requires adaption of soil conservations practices. However, farmers need more incentives then just improving soil health. Figure 1 demonstrates how soil conservation practices can concurrently increase SOM and productivity. In summary, increasing plant diversity and intensification results in:



  • higher biomass and grain production;

  • increases in abundance and diversity in soil fauna and microbial communities;

  • breaks up weed and pest cycles (reduces herbicide and insecticide inputs);

  • increases water use efficiency; and,

  • allows for incorporation of livestock into cropping systems.


Secondly, minimizing soil disturbance (i.e. no-tillage) to slow down the breakdown of SOM and always having something growing or at least keeping the ground covered (i.e. cover crops) results in:



  • higher organic matter accumulation;

  • greater water conservation;

  • reduces operation costs such as labor, fuel, machinery;

  • provides habitats for wildlife and beneficial insects; and,

  • aids in recovering of salt affected soils.


 Figure 1. System approach for improving soil health and productivity (Al-Kaisi, 2017). 


Investing in soil health goes beyond a farmer’s field. Lal et al., (2007) demonstrate that having soils in poor health lowers global food production, declines food security, limits economic options, directly affects human health, generates significant greenhouse gas emissions, and pollutes water resources. The same report also states that the prevention of soil degradation is much more cost effective than trying to restore degraded soils back to their original productivity. For farmers in NC region to improve sustainability and productivity on their land in the long-term, attention must be given on how soils can be managed to:



  • mitigate the effects of changing climate conditions (i.e. improve soil structure to increase water conservation);

  • produce more with less land and rising input cost (i.e. fertilizers and fuel); and,

  • adapting soil conservation practices to reduce further degradation of soil health.


Previous work by members of NC-174, NC-1017 and NC-1178 has demonstrated the importance of storing SOC (through increasing organic matter) for improving soil quality, including soil physical properties such as improved water holding capacity (Al-Kaisi et al., 2015; Guzman and Al-Kaisi, 2011; Lal, 1999). However, a strong connection between soil erosion and the global C balance has not been well established. There is also a need for developing sound methodology for obtaining a quantitative estimate of the actual distribution of soil C on various eroded and non-eroded landscapes in the Midwest. Also, there is a need to examine the alternative of intensified agroecosystems as a source for renewable fuel feedstock.  It was recognized during the Kyoto Protocol that net emissions of greenhouse gases, such as CO2 and CH4 could be decreased by either reducing emissions or by increasing the rate of C sequestration or retention in soils. Agricultural soils are one of the largest reservoirs of C, and thus have a great potential to mitigate the increasing concentration of CO2 in the atmosphere (FAO, 2001). Evaluation of the C pool in soils is difficult because of its heterogeneity in time and space (FAO, 2001). The global loss of C because of erosion is estimated to be in the range of 150 to 1500 million tons per year (Lal, 1995; Gregorich et al., 1998; Lal, 2003) but the processes are not well understood. Erosion is a selective process involving detachment and transport of the light soil fraction consisting of SOC and clay (Sharpley, 1985). The fate of eroded soil particles is complex depending on many parameters including soil properties, landscape elements and properties, drainage net and soil management. Many of the soil particles eroded are moved down slope and may remain in the same field or watershed for a considerable length of time (Olson et al., 2016a; Olson et al., 2016b).  However, this movement results in increased spatial variability of soil properties across the landscape, especially soil organic matter and those elements of environmental concern that are associated with it - carbon and nitrogen (Schumacher et al., 1999).


Rationale


This proposal outlines a project designed to help better understand changes in soil quality including soil degradation resulting from various crop management practices and the impact of intensified agroecosystems on soil health and soil carbon dynamics. It will also provide needed data on the changes in the soil C reservoir related to intensive land use for some of the major soils in the North Central region. This study will contribute to our understanding of soil-landscape processes with the potential to provide data that will contribute to improved management of our soil and water resources. We view this approach as a natural progression related to the past research efforts of NC-174, NC-1017, and NC-1178. Knowledge gained from the proposed research will contribute to a more quantitative understanding of the effects of intensified agroecosystem management on global C balance; erosional processes; the amounts and landscape distribution of C and organic matter; and changes in soil quality. The proposed regional research project will provide information that can be used to enable sustainable management of natural resources in different ecosystems, over the varying climates and soil landscapes that occur in the participating states. The findings from this project can provide baseline information on soil sustainability impacted by possible climate change such as increased intense rainfall events, decreased total precipitation, and increased temperatures.  In addition, this project will address a wide range of landscape and cropping systems in the Midwest that include row crop production and integration of livestock.  It is unique that it will focus on the impact of intensive management practices (i.e., tillage and row corps) and potential impact on soil health and water quality. The work of this project will expand the work of the predecessors ot this project over the past four decades that has had significant impact in terms of scholarly research and prolific production of publications in the promotion of conservation production systems that promote soil health.  This project continues to assemble a wide range of expertise coupled with a long-term continuum of members and participants to provide a platform for new researchers to develop research that addresses evolving issues in food production and environmental quality.

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