Haddish Melakeberhan

The co-existence of microbial communities and Meloidogyne hapla populations showing high, medium, and low levels of parasitic variability (PV) in mineral and muck soils with different soil health conditions in Michigan vegetable production fields is established. However, if PV relates or not to bacterial communities is unknown. This study characterized bacterial communities present on and in the body of nine M. hapla field and greenhouse sub-populations isolated from the mineral and muck fields. We utilized a high throughput sequencing of 16S rDNA. Results showed a variable composition (or abundance) of 65 genera in the field and 61 genera in the greenhouse isolates, with 12 genera of unknown and the rest belonging to 14 known functional groups. The medium- and low-PV populations shared more bacterial composition than either one with the high-PV population. Thus, laying a foundation for an in-depth understanding of if the observed associations have any role in cause-and-effect relationships with M. hapla PV.

Tillage, cover crops (CC) and nutrient amendments are regenerative agricultural practices (RAPs) which enhance desirable ecosystem services (DESs), including the beneficial nematode community structure (BNCS), soil organic matter (SOM), pH, and available nitrogen, and the Ferris et al. soil food web (SFW) model relates changes in the BNCS to biophysicochemical conditions generating DESs. However, the SFW model’s power to identify soil health conditions influencing DESs’ outcomes has been limited. We tested how tillage, winter rye CC, and 0, 112, or 224 kg N/ha from inorganic and compost sources affected the DESs after four years of corn production. The SOM and NO₃ was much greater in the no-till than the tilled soil, and the SOM in the 224 kg organic source, compared with the rest of the N rates, was significantly increased. The N recovery was not proportional to what was applied. The variable effects of the RAPs on the DESs suggest either changing or continuing treatments until suitable outcomes are achieved, all without knowing the source(s) of variability. The SFW model revealed primarily resource-limited and structured (Quadrant C) conditions, suggesting that (1) nutrient cycling needs biological activities and (2) the presence of a process-limiting factor may have contributed to the variable results. The impacts of the SFW model as a diagnostic tool are outlined.

The northern root-knot nematode (Meloidogyne hapla) causes extensive damage to agricultural crops globally. In addition, M. hapla populations with no known genetic or morphological differences exhibit parasitic variability (PV) or reproductive potential based on soil type. However, why M. hapla populations from mineral soil with degraded soil health conditions have a higher PV than populations from muck soil is unknown. To improve our understanding of soil bio-physicochemical conditions in the environment where M. hapla populations exhibited PV, this study characterized the soil microbial community and core- and indicator-species structure associated with M. hapla occurrence and soil health conditions in 15 Michigan mineral and muck vegetable production fields. Bacterial and fungal communities in soils from where nematodes were isolated were characterized with high throughput sequencing of 16S and internal transcribed spacer (ITS) rDNA. Our results showed that M. hapla-infested, as well as disturbed and degraded muck fields, had lower bacterial diversity (observed richness and Shannon) compared to corresponding mineral soil fields or non-infested mineral fields. Bacterial and fungal community abundance varied by soil group, soil health conditions, and/or M. hapla occurrence. A core microbial community was found to consist of 39 bacterial and 44 fungal sub-operational taxonomic units (OTUs) across all fields. In addition, 25 bacteria were resolved as indicator OTUs associated with M. hapla presence or absence, and 1,065 bacteria as indicator OTUs associated with soil health conditions. Out of the 1,065 bacterial OTUs, 73.9% indicated stable soil health, 8.4% disturbed, and 0.4% degraded condition; no indicators were common to the three categories. Collectively, these results provide a foundation for an in-depth understanding of the environment where M. hapla exists and conditions associated with parasitic variability.

Parasitic variability (PV) of Meloidogyne hapla populations exists in broad production landscapes. How PV relates to soil health as described by the soil food web (SFW) is unknown. In an experiment replicated three times, nine M. hapla populations from muck and mineral soils with degraded and disturbed SFW conditions from three regions were used to test a hypothesis that PV varies by SFW conditions. The populations were inoculated at 2000 and 4000 eggs in 300 cm³ soil per pot. While the populations’ reproductive potential varied by the SFW condition, soil group, region and/or their interactions, they clustered into high (Population 13), medium (Population 8), and low (all populations from muck and one from mineral soil) PV. Populations 8 and 13 are from degraded mineral soils and the low PV populations are from disturbed and degraded soils, indicating that the conditions where PV exists are variable within or across soil groups. Consequently, the hypothesis is not supported. Parasitic variability (PV) of Meloidogyne hapla populations exists in broad production landscapes. How PV relates to soil health as described by the soil food web (SFW) is unknown. In an experiment replicated three times, nine M. hapla populations from muck and mineral soils with degraded and disturbed SFW conditions from three regions were used to test a hypothesis that PV varies by SFW conditions. The populations were inoculated at 2000 and 4000 eggs in 300 cm³ soil per pot. While the populations’ reproductive potential varied by the SFW condition, soil group, region and/or their interactions, they clustered into high (Population 13), medium (Population 8), and low (all populations from muck and one from mineral soil) PV. Populations 8 and 13 are from degraded mineral soils and the low PV populations are from disturbed and degraded soils, indicating that the conditions where PV exists are variable within or across soil groups. Consequently, the hypothesis is not supported.

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. We define IPE as a concept that identifies best-to-worst-case soil health outcomes by assessing the effect of agronomic practices on weighted abundance of functional guilds (WAFG) of beneficial soil organisms and SHIs simultaneously. 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. We 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.

Soil health connotes the balance of biological, physicochemical, nutritional, structural, and water-holding components necessary to sustain plant productivity. Despite a substantial knowledge base, achieving sustainable soil health remains a goal because it is difficult to simultaneously: (i) improve soil structure, physicochemistry, water-holding capacity, and nutrient cycling; (ii) suppress pests and diseases while increasing beneficial organisms; and (iii) improve biological functioning leading to improved biomass/crop yield. The objectives of this review are (a) to identify agricultural practices (APs) driving soil health degradations and barriers to developing sustainable soil health, and (b) to describe how the nematode community analyses-based soil food web (SFW) and fertilizer use efficiency (FUE) data visualization models can be used towards developing sustainable soil health. The SFW model considers changes in beneficial nematode population dynamics relative to food and reproduction (enrichment index, EI; y-axis) and resistance to disturbance (structure index, SI; x-axis) in order to identify best-to-worst case scenarios for nutrient cycling and agroecosystem suitability of AP-driven outcomes. The FUE model visualizes associations between beneficial and plant-parasitic nematodes (x-axis) and ecosystem services (e.g., yield or nutrients, y-axis). The x-y relationship identifies best-to-worst case scenarios of the outcomes for sustainability. Both models can serve as platforms towards developing integrated and sustainable soil health management strategies on a location-specific or a one-size-fits-all basis. Future improvements for increased implementation of these models are discussed.

Determining if the vast soil health degradations across the seven major soil groups (orders) of Sub-Saharan Africa (SSA) can be managed on the basis of a one-size-fits-all or location-specific approach is limited by a lack of soil group-based understanding of soil health degradations. We used the relationship between changes in nematode population dynamics relative to food and reproduction (enrichment, EI) and resistance to disturbance (structure, SI) indices to characterize the soil food web (SFW) and soil health conditions of Ferralsol, Lithosol and Nitosol soil groups in Ghana, Kenya and Malawi. We applied bivariate correlations of EI, SI, soil pH, soil organic carbon (SOC), and texture (sand, silt and clay) to identify integrated indicator parameters, and principal component analysis (PCA) to determine how all measured parameters, soil groups, and countries align. A total of 512 georeferenced soil samples from disturbed (agricultural) and undisturbed (natural vegetation) landscapes were analyzed. Nematode trophic group abundance was low and varied by soil group, landscape and country. The resource-limited and degraded SFW conditions separated by soil groups and by country. EI and SI correlation with SOC varied by landscape, soil group or country. PCA alignment showed separation of soil groups within and across countries. The study developed the first biophysicochemical proof-of-concept that the soil groups need to be treated separately when formulating scalable soil health management strategies in SSA.

A substantial knowledge gap exists on how compost source and rate of application affect nematode community-based soil food web structure, soil health, soil physiochemistry, and crop yield and quality in short- and full-season crops. We tested effects of plant (PC)- and animal (AC)-based compost at 1, 1.5 and 2× the standard nitrogen (N) rate on processing carrot ‘Cupar’ and fresh market ‘Sugarsnax 54’ (short-season crop) over 2-3 growing seasons. Low abundance of nematodes and domination of herbivores and bacterivores indicate that the field is biologically stressed. While outcomes of most measured parameters varied by compost source and/or rate, an increase in soil food web structure with time was most consistent. A combination of the variable outcomes and correlation patterns suggest that a multifactor analysis may best quantify compost-driven changes in soil ecosystems as opposed to looking for changes in a single parameter.

Preventive and/or manipulative practices will be needed to maintain soil's biological, physiochemical, nutritional, and structural health in natural, managed, and disturbed ecosystems as a foundation for food security and global ecosystem sustainability. While there is a substantial body of interdisciplinary science on understanding function and structure of soil ecosystems, key gaps must be bridged in assessing integrated agro-biological, ecological, economical, and environmental efficiency of soil manipulation practices in time and space across ecosystems. This presentation discusses the application of a fertilizer use efficiency (FUE) model for assessing agronomic, economic, ecological, environmental, and nematode (pest) management efficiency of soil amendments. FUE is defined as increase in host productivity and/or decrease in plant-parasitic nematode population density in response to a given fertilizer treatment. Using the effects of nutrient amendment on Heterodera glycines population density and normalized difference vegetative index (indicator of physiological activities) of a soybean cultivar 'CX 252', how the FUE model recognizes variable responses and separates nutrient deficiency and toxicity from nematode parasitism as well as suitability of treatments designed to achieve desired biological and physiochemical soil health conditions is demonstrated. As part of bridging gaps between agricultural and ecological approaches to integrated understanding and management of soil health, modifications of the FUE model for analyzing the relationships amongst nematode community structure, soil parameters (eg. pH, nutrients, %OM), and plant response to soil amendment is discussed.

Developing multi-purpose alternatives to synthetic nematicides for managing the northern root-knot nematode, Meloidogyne hapla, a problem in a variety of temperate vegetable and nursery crop production soils, continues to be challenging. Arugula (Eruca sativa), a high-end green vegetable crop with biofumigant and cover crop attributes, is an effective trap crop (dead-end host) for populations of M. hapla in sandy loam soil. Exploiting arugula's multi-purpose attributes, however, depends on understanding its interaction with M. hapla under a range of conditions. The objectives of this study were to determine if soil types affect: i) the ability of M. hapla to infect arugula; and ii) if M. hapla infection has any effect on arugula's vegetative quality in the respective soils. When 2-week-old arugula cv. Roquette seedlings were inoculated with either 0 (control), 4000 or 8000 M. hapla eggs per 300 cm3 of either sandy, sandy loam or muck soil, and maintained for 23 and 24 days (28±2°C), more nematodes were recovered from sandy loam soil. However, the numbers of nematodes recovered between the inocula were similar in the three soil types and nematode infection had no effect on plant growth or nutritional quality. However, the growth and leaf nutritional quantity of arugula were significantly affected by soil type. The results support the hypothesis that M. hapla will infect arugula in different soil types without affecting its vegetative quantity and quality, providing the basis for testing arugula's trap, vegetable and, possibly, biofumigant attributes from one seeding in fields where M. hapla exists.