Percent soil organic matter (SOM), pH and crop yield are among the biophysicochemical process-driven soil health indicators (SHIs). However, identifying sustainable soil health conditions using these SHIs is limited due to the lack of Integrated Productivity Efficiency (IPE) models. Expressing WAFG of all beneficial nematodes (x-axis) and SHIs (y-axis) as a percent of untreated control and regression of x and y reveals four quadrants describing worst-to-best-case outcomes for soil health and sustainability. And tested the effects of composted cow manure (AC) and plant litter (PC) applied at 135 (1×), 203 (1.5×), and 270 (2×) kg N/ha on WAFG, SOM, pH, and yield in a sandy clay loam field of a processing carrot cultivar over three growing seasons. Untreated control and urea at 1× served as experimental controls. Data that varied by time and were difficult to make sense of were separated into sustainable, unsustainable, or requiring specific modification to be sustainable categories by the IPE model. Within the sustainable category, all AC treatments and 2× rate of PC treatments had the best integrated efficiency outcomes across the SHIs. The IPE model provides a platform where other biophysicochemical process-driven SHIs could be integrated.
1. Achieving Steady-State and Sustainable Soil Health Using Agricultural Practices (APs)
The application of soil nutrient amendments are among the agricultural practices (APs) used to achieve healthy soil in crop production systems
[1][2][3][4][5][6]. Soil health, defined as capacity of a soil to function, has biological, physicochemical, nutritional, structural and water holding integrity components that need to be kept in balance in order to generate the desired ecosystem services
[7][8][9]. Percent soil organic matter (SOM), pH, and crop yield are among the broad indicators of biophysicochemical process-driven soil health outcomes. Despite a substantial basic and applied science knowledge on the components of soil health and the biophysicochemical processes generating the desirable ecosystem services, developing sustainable soil health conditions remains a goal
[10][11][12][13][14][15].
A sustainable soil health is defined as one that (i) has ideal conditions that deliver the desirable ecosystem services and meets (ii) environmental and (iii) economic expectations simultaneously
[9]. There are two major factors that limit identifying and developing sustainable soil health. The first factor is the lack of an integrated understanding of how the APs influence the different components of soil health, the biophysicochemical process that generate the desired ecosystem services, and an indicator that connects the outcomes. Nematodes, most abundant metazoan on the planet and central players in the soil food web (SFW) and nutrient cycling, are a key indicator of belowground biophysicochemical and ecological changes
[16][17][18][19][20][21][22][23][24][25][26]. The Ferris et al.
[17] SFW model that identifies best-to-worst case scenarios for nutrient cycling potential and agroecosystem suitability by measuring changes in beneficial nematode population dynamics relative to reproduction and food source (enrichment trajectory) and to disturbance (structure trajectory) is an example. The SFW model’s application has been expanded to identify soil health conditions
[9][27]. The second limiting factor is the lack of integration platforms that identify if the outcomes meet the definition of sustainable soil health
[7][9]. Integration platform is defined as a foundation where desired ecosystem services can be aligned collectively or on a step-by-step basis. This requires integrated efficiency assessment that considers multiple ecosystem services simultaneously and identifies if the outcomes meet agrobiological, environmental and economic expectations.
2. The Concept of Integrated Efficiency and the Role of Nematodes
The concept of integrated efficiency has been reviewed recently
[9]. Briefly, the common way of determining if an AP works or not is to assess production efficiency and sustainability of the ecosystem services in the soil. In the current context, here define production efficiency as the difference between the values of inputs (e.g., soil amendment or fertilizer) and outcomes (e.g., increases in organic matter or yield). For example, yield increases on a per-unit-nutrient and/or amount-of-fertilizer-applied basis would be considered efficient by current soil fertility management standards
[20][28][29][30][31]. However, efficiency analysis based on increase of yield alone does not always lead to determining system sustainability. i.e., if a soil nutrient amendment increases crop yield, but adversely affects the soil environment
[32] or beneficial organisms, it may not be sustainable
[14][15]. Sustainability requires integration of the different components of soil health and multiple biophysicochemical process-driven ecosystem services simultaneously.
The modified nematode community analysis-based Fertilizer Use Efficiency (FUE) model demonstrates how multiple ecosystem services can simultaneously be considered to identify sustainable soil health conditions. The FUE model separates nutrient deficiency and toxicity from effect on beneficial nematodes, desired ecosystem service (agronomic or soil parameter), and environmental outcomes and promotes identification of APs that lead to sustainable soil health conditions. The FUE model measures changes in abundance of beneficial nematodes quantified at trophic group levels (e.g., bacterivore, fungivore, predator or omnivore
[20]) as an indicator
[33]. It uses a quadrant format to relate production efficiency in terms of soil nutrients in relation to the abundances of beneficial nematodes as a percentage of those of the untreated control. Plotting production efficiency as crop yield or soil nutrient parameters (
y-axis) against beneficial nematode trophic group abundance (
x-axis) provides four categories of graphical indicators of the condition of the production system.
An optimal and potentially sustainable outcome is that a set of APs result in an increase of the biophysicochemical process-driven desired ecosystem services (soil parameter or yield) and abundance of beneficial nematodes (Quadrant F). A decrease in desired ecosystem service and beneficial nematodes (Quadrant G) indicates an unfavorable soil health outcome. If the outcome is an increase in desired ecosystem service and a decrease in beneficial nematodes (Quadrant E), the AP has conflicting consequences. A similarly conflicting consequence occurs when there is a decrease in ecosystem service with an increase in beneficial nematodes (Quadrant H).
The FUE model identifies best-to-worst case outcomes for sustainability by treating beneficial nematodes quantified at the trophic level (bacterivore, fungivore, predator and omnivore
[16][17]) as a group and without accounting for their functions
[33]. By feeding on microbes and being food for others, beneficial nematodes are contributing to the biophysicochemical processes of the SFW. In order to integrate the biophysicochemical process-based changes that nematodes contribute to and influence soil health, their functional guilds from colonizer-persister (c-p) to trophic levels need to be considered. This requires a new concept of Integrated Production Efficiency (IPE) analysis.
3. The Concept of IPE
Here propose an IPE model that simultaneously considers soil biophysicochemical process-driven changes, environmental consequences, yield, and economics associated with the APs. Then define IPE as a measure of the sustainability of production management practices and the outcomes in their totality. The IPE model uses new weighted abundances of functional guilds (WAFG) of beneficial nematodes quantified at the trophic
[20] and c-p levels
[16][17] as an indicator of biological changes to identify best-to-worst outcomes for sustainability and sustainable soil health conditions. What makes the IPE model unique is that it combines numbers and functions of bacterivore, fungivore, predator and omnivore nematode trophic groups
[16][17] and compares changes of SHIs relative to one-another and identifies if the outcome is sustainable, unsustainable, and what specific actions will be required to get the desired outcome. By accounting for the numerical and functional aspects of nematodes, the IPE model (a) provides a broader assessment of biophysicochemical changes in the soil ecosystem that the APs drive, and (b) creates a platform where outcomes of different soil health components could be integrated.
4. Goals and Objectives
The long-term goal is to develop IPE footprints that will lead to identifying sustainable soil health management in cropping systems from a single core of soil. The objectives of the entry were three-fold: First, to introduce a new WAFG into the IPE model to recognize nematode community structures and their functions. This is important because there are no specific soil health values associated with either nematode trophic and/or c-p group abundance. Under these circumstances, it is necessary to consider changes in total nematode abundance that account for AP disturbance-driven c-p to trophic level dynamics and integrate WAFG of all nematodes into the IPE model. The WAFG will provide a measure of the total changes that could be attributed to nematodes. Second, to test the IPE model using the effects of plant (PC) and animal (AC) based compost amendments on soil pH, SOM and yield of carrot.