Soil Health
Soil health is defined as the continued capacity of the soil to function as a vital living ecosystem that sustains plants, animals, and humans (NRCS, 2023). It also serves as an overarching principle guiding production agriculture toward its goals of sustainability and climate adaptation and mitigation. As a movement, soil health has spurred efforts, policies, and innovations to identify and promote conservation practices and to monitor, measure, and verify soil health gains in managed land over the years. Our team proposed the concepts of 'Soil Health Gap' and 'Soil Health Cycle' to further the science of soil health.
Soil Health Cycle
Inspired by a Nebraska Soil Health School survey comment, Dr. Maharjan conceptualized the Soil Health Cycle (SHC) as an iterative soil health management cycle to achieve agricultural sustainability.
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The SHC is a feedback cycle in soil health management comprised of a series of interdependent entities and steps that involve human dimensions affecting decisions on agricultural practices, their impact assessment, and making inferences to iterate the process accounting for site-specific resource constraint and complex agroecosystems to achieve iterative soil health improvement.
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The SHC offers a systematic approach to integrating soil health practices, measuring soil health benefits due to soil health management in terms of productivity, profitability, and environmental benefits and their cumulative impact on policy, economic factors, and human dimensions, which sets the cycle revolving.
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Soil Health Cycle, Maharjan et al
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Soil Health Gap
Growing calls and the need for sustainable agriculture have brought deserved attention to soil and to efforts towards improving or maintaining soil health. Numerous research and field experiments report soil health in terms of physicochemical and biological indicators and identify different management practices that can improve it. However, the question remains: How much of cultivated land has been degraded since the dawn of agriculture? What is the maximum or realistically attainable soil health goal? Determination of a benchmark that defines the true magnitude of degradation and simultaneously sets potential soil health goals will optimize efforts in improving soil health using different practices. Our team coined a new term, “Soil Health Gap,” which is defined as the difference between soil health in an undisturbed native soil and current soil health in a cropland in a given agroecosystem. Soil Health Gap can be determined based on a general or specific soil property such as soil carbon.
We measured soil organic carbon at native grassland, no-till, conventionally tilled, and subsoil-exposed farmlands in Scotts Bluff County, NE. Soil Health Gap based on soil organic carbon was in the order of no-till < conventional till < subsoil exposed farmland, and subsequently, the maximum attainable soil health goal with the introduction of conservation practices would vary by an existing management practice or condition. Soil Health Gap establishes a benchmark for soil health management decisions and goals and can be scaled up from site-specific to regional to global scale.
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Soil Health Gap: A concept to establish a benchmark for soil health management - ScienceDirect, Maharjan et al
Cropland Reference Ecological Unit
There is a growing consensus on the need to measure the dynamic soil properties of croplands and even comparisons with a reference state or native land. These measurements and paired comparisons will create the capacity to determine soil health management effects and targets. However, the complex soil heterogeneity and climate variations make soil health potential variable and confound the effects of land-use and management practices and comparisons between soils from different sites. Identifying a discrete landmass unit where all soils have similar health potential will be critical in conducting meaningful comparative studies and measuring the impact of conservation practices. This methodological paper proposes and discusses a land unit, Cropland Reference Ecological Unit (CREU), that accounts for soil genoform and climate variabilities and covers an area with a presumably similar soil health potential. An example CREU has been developed, for one Major Land Resource Area (MLRA) in Nebraska, which is an area delineated based on the standard United States Department of Agriculture – Natural Resources Conservation Service (USDA-NRCS) hierarchical land classification system. This example portrays an actual difference in soil health for different land use, and agronomic management practices can be determined by comparing sites under the framework of CREU. Evaluation of management effects on soil health indicators in a CREU will adequately illustrate the beneficial impact of such practices without being confounded by agroecological variations. This proposed framework addresses researchers’ current interest in comparing soil health parameters among croplands and reference sites to benchmark soil health measurements, set soil health targets, and determine the effects of different management practices.
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Cropland Reference Ecological Unit: A land classification unit for comparative soil studies - ScienceDirect, Das and Maharjan