Soil Abiotic Factors Research Articles

Microbial and Enzyme Activities of Saline and Sodic Soils

AbstractSalinization and sodication are abiotic soil factors, important hazards to soil fertility and consequently affect the crop production. Soil salinization is of great concern for irrigated agriculture in arid and semi‐arid regions of the world; sodicity is characterized by an excessively high concentration of sodium (Na) in their cation exchange system. In recent times, attention has been turned to study the impacts of these factors (salinity and sodicity) on soil microbial activities. Microbial activities play central role in degradation and decomposition of soil organic matter, mineralization of nutrients and stabilization of soil aggregates. To understand the ecology of soil system, therefore, it is important to be conversant with the soil microbial activities, which show quick response to little change in the soil environment. Microbial activities (generally measured as C–N dynamics, soil respiration–basal respiration, or CO2 emission), microbial abundance, microbial biomass, quotients (microbial and metabolic) and microbial community structure, and soil enzymes have been considered as potential indicators to assess the severity of the land degradation and the effectiveness of land use management. Therefore, it is important to synthesize the available information regarding microbial activities in use and management of salt‐affected soils. The reclamation and management of such soils and their physico‐chemical properties have been reviewed well in the literature. In this review, an attempt has been made to compile the current knowledge about the effects of soil salinization and sodication on microbial and enzyme activities and identify research gaps for future research. Copyright © 2015 John Wiley & Sons, Ltd.

Contribution of above- and below-ground plant traits to the structure and function of grassland soil microbial communities.

Abiotic properties of soil are known to be major drivers of the microbial community within it. Our understanding of how soil microbial properties are related to the functional structure and diversity of plant communities, however, is limited and largely restricted to above-ground plant traits, with the role of below-ground traits being poorly understood. This study investigated the relative contributions of soil abiotic properties and plant traits, both above-ground and below-ground, to variations in microbial processes involved in grassland nitrogen turnover. In mountain grasslands distributed across three European sites, a correlative approach was used to examine the role of a large range of plant functional traits and soil abiotic factors on microbial variables, including gene abundance of nitrifiers and denitrifiers and their potential activities. Direct effects of soil abiotic parameters were found to have the most significant influence on the microbial groups investigated. Indirect pathways via plant functional traits contributed substantially to explaining the relative abundance of fungi and bacteria and gene abundances of the investigated microbial communities, while they explained little of the variance in microbial activities. Gene abundances of nitrifiers and denitrifiers were most strongly related to below-ground plant traits, suggesting that they were the most relevant traits for explaining variation in community structure and abundances of soil microbes involved in nitrification and denitrification. The results suggest that consideration of plant traits, and especially below-ground traits, increases our ability to describe variation in the abundances and the functional characteristics of microbial communities in grassland soils.

Belowground carbon allocation by trees, understory vegetation and soil type alter microbial community composition and nutrient cycling in tropical Eucalyptus plantations

We studied the influence of plant functional groups on soil microbial community composition and nutrient cycling in a tropical Eucalyptus forest ecosystem with different plantation age and soil types by means of stem girdling (SG) and understory removal (UR). Fungal and bacterial communities were characterized using phospholipid fatty acids, and ectomycorrhizal fungi (EMF) colonisation was estimated visually. Total bacterial and saprotrophic fungal biomass was highest in soils treated with SG, followed by UR, through modification of plant belowground C allocation and N supply. EMF root colonisation, biomass of EMF, arbuscular mycorrhizal fungi (AMF) and the fungal-to-bacterial ratio were lowest in these soils. We found that EMF, AMF and the fungal-to-bacterial ratio were highest in sandy loam soils with a high C/N ratio and low pH. The fungal-to-bacterial ratio was higher in 5-year-old than in 15-year-old plantation. We propose that girdling of trees and removal of understory plants are important ecological components, due to their modification of plant belowground C allocation and N supply as key determinants of microbial community composition. Our results highlight the fact that soil abiotic factors play an important role in shaping the microbial community and nutrient cycling in tropical forest ecosystems.

Soil Biotic and Abiotic Responses to Dimethyl Disulfide Spot Drip Fumigation in Established Grape Vines

Dimethyl disulfide (DMDS) is a soil fumigant used in agricultural systems as an alternative to methyl bromide (MeBr) for the control of soilborne pests and pathogens. However, fumigants including DMDS that have broad biocidal activity can affect both target and non-target organisms in soil. This study focused on the effects of DMDS on the recovery of ecologically important microbial communities and soil abiotic factors while affecting plant parasitic nematodes in both field and microplot trials. Phospholipid fatty acid (PLFA) analysis was used to characterize changes in microbial community structure over time. Total amount of PLFA as well as all major non-target soil microbial groups such as Gram positive bacteria, Gram negative bacteria, fungi, arbuscular mycorrhizal fungi (AMF), and actinomycetes decreased significantly 15 d after fumigation in the untreated control as well as in all the rates of DMDS tested in a microplot trial. Fumigation had little effect on microbial biomass but at some time points some treatments did affect microbial community structure. Canonical multivariate analysis of variance indicated that soil microbial communities 45, 60, and 90 d after fumigation were similar to one another compared with 15 d after fumigation. The research showed that reduction and changes in microbial community biomass and structure were mainly due to environmental factors and therefore, it is concluded that DMDS fumigation did not impact the activity of beneficial microorganisms. Total N, C, and other abiotic factors were also not affected by DMDS fumigation. Plant parasitic nematodes were greatly affected by DMDS fumigation and this interaction could be related to its mode of action which affects nematode mitochondrial activity.

Savanna browse production. 1: Determinants and measurement

With the rapid expansion of wildlife ranching and conservation in South African savannas and the resultant increase in multi-species grazing and browsing systems, information on browse production potential is essential for determination of carrying capacity. This study, conducted on three game reserves in the northern Zululand coastal plains of KwaZulu-Natal, explored the biotic (measurable tree dimensions, and tree species) and abiotic (climatic and soil) factors influencing the rate and quantity of quarterly browse production of seven key savanna tree species (Acacia nilotica [Vachellia nilotica], Carissa bispinosa, Dichrostachys cinerea, Euclea divinorum, Gymnosporia senegalensis, Spirostachys africana and Ziziphus mucronata). Available canopy volume, mean maximum daily temperature and tree species were the most significant determinants of browse production. Available canopy volume proved to be the most reliable predictor of browse production per species and per tree, with quarterly browse production being greater on trees with larger available canopy volumes (up to a threshold). Browse production differed significantly between quarters. Growing season onset occurred during the sampling period prior to the rainy season when mean maximum daily temperatures peaked. Quarterly browse production was greatest in evergreen E. divinorum, followed by the semi-deciduous species, S. africana and Z. mucronata.

Soil invertebrate fauna affect N2O emissions from soil

Nitrous oxide (N2 O) emissions from soils contribute significantly to global warming. Mitigation of N2 O emissions is severely hampered by a lack of understanding of its main controls. Fluxes can only partly be predicted from soil abiotic factors and microbial analyses - a possible role for soil fauna has until now largely been overlooked. We studied the effect of six groups of soil invertebrate fauna and tested the hypothesis that all of them increase N2 O emissions, although to different extents. We conducted three microcosm experiments with sandy soil and hay residue. Faunal groups included in our experiments were as follows: fungal-feeding nematodes, mites, springtails, potworms, earthworms and isopods. In experiment I, involving all six faunal groups, N2 O emissions declined with earthworms and potworms from 78.4 (control) to 37.0 (earthworms) or 53.5 (potworms) mg N2 O-N m(-2) . In experiment II, with a higher soil-to-hay ratio and mites, springtails and potworms as faunal treatments, N2 O emissions increased with potworms from 51.9 (control) to 123.5 mg N2 O-N m(-2) . Experiment III studied the effect of potworm density; we found that higher densities of potworms accelerated the peak of the N2 O emissions by 5 days (P < 0.001), but the cumulative N2 O emissions remained unaffected. We propose that increased soil aeration by the soil fauna reduced N2 O emissions in experiment I, whereas in experiment II N2 O emissions were driven by increased nitrogen and carbon availability. In experiment III, higher densities of potworms accelerated nitrogen and carbon availability and N2 O emissions, but did not increase them. Overall, our data show that soil fauna can suppress, increase, delay or accelerate N2 O emissions from soil and should therefore be an integral part of future N2 O studies.

Soil abiotic factors influence interactions between belowground herbivores and plant roots

Root herbivores are important ecosystem drivers and agricultural pests, and, possibly as a consequence, plants protect their roots using a variety of defensive strategies. One aspect that distinguishes belowground from aboveground plant-insect interactions is that roots are constantly exposed to a set of soil-specific abiotic factors. These factors can profoundly influence root resistance, and, consequently, the outcome of the interaction with belowground feeders. In this review, we synthesize the current literature on the impact of soil moisture, nutrients, and texture on root-herbivore interactions. We show that soil abiotic factors influence the interaction by modulating herbivore abundance and behaviour, root growth and resistance, beneficial microorganisms, as well as natural enemies of the herbivores. We suggest that abiotic heterogeneity may explain the high variability that is often encountered in root-herbivore systems. We also propose that under abiotic stress, the relative fitness value of the roots and the potential negative impact of herbivory increases, which may lead to a higher defensive investment and an increased recruitment of beneficial microorganisms by the plant. At the same time, both root-feeding herbivores and natural enemies are likely to decrease in abundance under extreme environmental conditions, leading to a context- and species-specific impact on plant fitness. Only by using tightly controlled experiments that include soil abiotic heterogeneity will it be possible to understand the impact of root feeders on an ecosystem scale and to develop predictive models for pest occurrence and impact.

Adaptive divergence in seed color camouflage in contrasting soil environments

Although adaptive plant population divergence across contrasting soil conditions is often driven by abiotic soil factors, natural enemies may also contribute. Cryptic matching to the native soil color is a form of defensive camouflage that seeds can use to avoid detection by seed predators. The legume Acmispon wrangelianus occurs across a variety of gray-green serpentine soils and brown nonserpentine soils. Quantitative digital image analysis of seed and soil colors was used to test whether genetically based seed color is a closer match to the color of the native soil than to the color of other nearby soils. Lineages bear seeds that more closely match the color of their native serpentine or nonserpentine soil type than the opposing soil type. Further, even within a soil type, lineages bear seeds with a closer color match to the soil at their native site than to other sites. The striking concordance between seed and native soil color suggests that natural selection for locally camouflaged seed color morphs, probably driven by seed predators, may maintain adaptive divergence in pigmentation, despite the opportunity for migration between soil environments.

Acidobacterial community responses to agricultural management of soybean in Amazon forest soils

This study focused on the impact of land-use changes and agricultural management of soybean in Amazon forest soils on the abundance and composition of the acidobacterial community. Quantitative real-time PCR (q-PCR) assays and pyrosequencing of 16S rRNA gene were applied to study the acidobacterial community in bulk soil samples from soybean croplands and adjacent native forests, and mesocosm soil samples from soybean rhizosphere. Based on qPCR measurements, Acidobacteria accounted for 23% in forest soils, 18% in cropland soils, and 14% in soybean rhizosphere of the total bacterial signals. From the 16S rRNA gene sequences of Bacteria domain, the phylum Acidobacteria represented 28% of the sequences from forest soils, 16% from cropland soils, and 17% from soybean rhizosphere. Acidobacteria subgroups 1-8, 10, 11, 13, 17, 18, 22, and 25 were detected with subgroup 1 as dominant among them. Subgroups 4, 6, and 7 were significantly higher in cropland soils than in forest soils, which subgroups responded to decrease in soil aluminum. Subgroups 6 and 7 responded to high content of soil Ca, Mg, Mn, and B. These results showed a differential response of the Acidobacteria subgroups to abiotic soil factors, and open the possibilities to explore acidobacterial subgroups as early-warning bioindicators of agricultural soil management effects in the Amazon area.

The Response of Soil Nematode Community to Nitrogen, Water, and Grazing History in the Inner Mongolian Steppe, China

Nutrient nitrogen and water availability are co-limiting factors for grassland productivity in the Inner Mongolian steppe. The objective of this study was to evaluate the interactive effects of water and nitrogen (N) addition on soil abiotic factors and soil nematode community composition. A 3-year experiment with addition of water (with and without irrigation simulating wet year precipitation) and nitrogen (0, 25, and 50 kg N ha−1) was conducted at two sites in Inner Mongolia with histories of heavy grazing (HG) and moderate grazing (MG). The results showed that HG had several lower nematode ecological indicators; namely, the Simpson index (P < 0.01), maturity index (MI, including free-living nematodes), and plant parasite index (PPI, including plant-parasitic nematodes). In addition, HG had a lower proportion of omnivores–predators and higher proportion of bacterivores (P < 0.01), with reduced soil moisture, total nitrogen and total carbon (C), and increased C/N ratio. A relatively low addition of N did not influence soil total carbon and total nitrogen and had only a slight effect on the composition and structure of the soil nematode community. Water addition increased the proportion of plant parasites, reduced the proportion of bacterivores and omnivores–predators and increased the soil total carbon and total nitrogen. Redundancy analysis revealed that grazing history alone explained more variation in nematode taxon composition (17.4%, P < 0.01) and PPI (35.6%, P < 0.01) and MI (17.5%, P < 0.01) and Simpson index (10.5%, P < 0.01). Water addition explained more variation in the nematode feeding group (24.4%, P < 0.01), total nematodes (7.9%, P < 0.01) and PPI (78.7%, P < 0.01). Nitrogen addition explained variation in the nematode taxon composition (6.2%, P < 0.01). These results suggested that HG caused soil degradation, and water addition facilitated plant parasites and enhanced soil properties, whereas application of small amounts of nitrogen to N-limited semiarid grasslands did not induce clear changes in this system in the short term.

Is Mundulla Yellows really a threat to undisturbed native vegetation? A comment

Summary The term Mundulla Yellows (MY) was coined in 1997 to refer to a dieback disorder involving leaf chlorosis which affects Eucalyptus and other native southern Australian vascular plants. It was thought to be a new, spreading, contagious biotic disease with the potential to devastate native vegetation. Since then, research has found no evidence to confirm any role of biotic agents and generally the disorder has been more convincingly attributed to abiotic soil factors. It has now been suggested that most or all of the reported cases of MY are simply the very well-known nutrient disorder of alkaline soils, lime-induced chlorosis. All of the well-documented records of MY are from sites where acidic soils have become more alkaline because of the use of crushed limestone in road-making or to the use of alkaline irrigation water; none are from undisturbed native vegetation. Despite this research and much circumstantial evidence, the view that MY poses a grave risk to undisturbed vegetation still persists and needs to be corrected accordingly.

Do abiotic factors cause a gradual yield decline under continuous aerobic rice cultivation? A pot experiment with affected field soils

Aerobic rice is a water-saving technology in which rice grows in non-puddled and non-saturated (aerobic) soil without ponded water. A gradual decline in rice yield was found in field plots at the farm of the International Rice Research Institute, Los Baños, Philippines, where rice has been cultivated continuously for 10 cropping seasons under aerobic rice conditions. We investigated whether abiotic soil factors lead to the observed yield decline. An aerobic rice pot experiment was conducted using field soils from flooded rice plots and from the 10-season-long aerobic rice cultivated plots (referred to as 1st-season and 11th-season aerobic rice, respectively). Subtreatments consisted of soil sterilization by oven heating (at 95°C or higher for 24 h) and a control treatment. The above-ground biomass of 1st-season aerobic rice was significantly greater than that of 11th-season aerobic rice in both the oven-heating and control treatments. Oven heating increased soil N availability and above-ground biomass accumulation over the control in both 1st-season and 11th-season aerobic rice, but the above-ground biomass in the oven-heated 11th-season aerobic rice was still significantly lower than that of the oven-heated and even the untreated (control) 1st-season aerobic rice. These results suggest that abiotic factors contribute to the gradual yield decline observed in the field plots.

Interrelationships between mycorrhizal symbiosis, soil pH and plant sex modify the performance of Antennaria dioica

AM symbiosis is usually beneficial for plants, but the benefits gained may depend on the soil abiotic factors. In dioecious plants, female and male individuals have different resource demands and allocation patterns. As a consequence of these differences, it is logical to assume that female and male plants differ in their relationship with arbuscular mycorrhizal (AM) fungi, although this has rarely been examined. We used a factorial greenhouse experiment to investigate whether female and male plants in the dioecious model species Antennaria dioica have a different relationship with their AM symbionts under two soil pH levels. In particular, we asked: (1) Do the sexes in A. dioica have sex-specific benefits from AM symbiosis? (2) If so, which sex gains the highest benefit? (3) How does soil pH affect the sex – AM fungal relationship? Our results indicate that the sexes responded similarly to AM symbiosis and pH when mycorrhizal benefit was examined as growth and phosphorus accumulation. However, the sexes differed in response to AM symbiosis in terms of survival, as mortality was increased due to AM symbiosis in female plants whilst the opposite effect was detected in males. The plant–AM fungus relationship was significantly affected by soil pH as lowering the soil pH decreased the benefits gained by the plants from the mycorrhizal fungus. Taken together, our findings indicate that AM symbiosis is beneficial for plants depending on the life history trait considered. In addition, interactions between plants and their AM symbionts are modified by soil factors and the sex of the plant.

Influence of plant species and soil conditions on plant–soil feedback in mixed grassland communities

Summary 1. Our aim was to explore plant–soil feedback in mixed grassland communities and its significance for plant productivity and community composition relative to abiotic factors of soil type and fertility. 2. We carried out a 4‐year, field‐based mesocosm experiment to determine the relative effects of soil type, historic management intensity and soil conditioning by a wide range of plant species of mesotrophic grassland on the productivity and evenness of subsequent mixed communities. 3. The study consisted of an initial soil conditioning phase, whereby soil from two locations each with two levels of management intensity was conditioned with monocultures of nine grassland species, and a subsequent feedback phase, where mixed communities of the nine species were grown in conditioned soil to determine relative effects of experimental factors on the productivity and evenness of mixed communities and individual plant species performance. 4. In the conditioning phase of the experiment, individual plant species differentially influenced soil microbial communities and nutrient availability. However, these biotic effects were much less important as drivers of soil microbial properties and nutrient availability than were abiotic factors of soil type and fertility. 5. Significant feedback effects of conditioning were detected during the second phase of the study in terms of individual plant growth in mixed communities. These feedback effects were generally independent of soil type or fertility, and were consistently negative in nature. In most cases, individual plant species performed less well in mixed communities planted in soil that had previously supported their own species. 6. Synthesis. These findings suggest that despite soil abiotic factors acting as major drivers of soil microbial communities and nutrient availability, biotic interactions in the form of negative feedback play a significant role in regulating individual plant performance in mixed grassland communities across a range of soil conditions.

Relative roles of niche and neutral processes in structuring a soil microbial community

Most attempts to identify the processes that structure natural communities have focused on conspicuous macroorganisms whereas the processes responsible for structuring microbial communities remain relatively unknown. Two main theories explaining these processes have emerged; niche theory, which highlights the importance of deterministic processes, and neutral theory, which focuses on stochastic processes. We examined whether neutral or niche-based mechanisms best explain the composition and structure of communities of a functionally important soil microbe, the arbuscular mycorrhizal (AM) fungi. Using molecular techniques, we surveyed AM fungi from 425 individual plants of 28 plant species along a soil pH gradient. There was evidence that both niche and neutral processes structured this community. Species abundances fitted the zero-sum multinomial distribution and there was evidence of dispersal limitation, both indicators of neutral processes. However, we found stronger support that niche differentiation based on abiotic soil factors, primarily pH, was structuring the AM fungal community. Host plant species affected AM fungal community composition negligibly compared to soil pH. We conclude that although niche partitioning was the primary mechanism regulating the composition and diversity of natural AM fungal communities, these communities are also influenced by stochastic-neutral processes. This study represents one of the most comprehensive investigations of community-level processes acting on soil microbes; revealing a community that although influenced by stochastic processes, still responded in a predictable manner to a major abiotic niche axis, soil pH. The strong response to environmental factors of this community highlights the susceptibility of soil microbes to environmental change.

Spatial and temporal diversity of methanotrophs in a landfill cover soil are differentially related to soil abiotic factors

Methanotrophs present in landfill cover soil can limit methane emissions from landfill sites by oxidizing methane produced in landfill. Understanding the spatial and temporal distribution of populations of methanotrophs and the factors influencing their activity and diversity in landfill cover soil is critical to devise better landfill cover soil management strategies. pmoA-based microarray analyses of methanotroph community structure revealed a temporal shift in methanotroph populations across different seasons. Type II methanotrophs (particularly Methylocystis sp.) were found to be present across all seasons. Minor shifts in type I methanotroph populations were observed. In the case of spatial distribution, only minor differences in methanotroph community structure were observed with no recognizable patterns (both vertical and horizontal) at a 5 m scale. Correlation analysis between soil abiotic parameters (total C, N, NH4 (+) , NO3 (-) and water content) and distribution of methanotrophs revealed a lack of conclusive evidence for any distinct correlation pattern between measured abiotic parameters and methanotroph community structure, suggesting that complex interactions of several physico-chemical parameters shape methanotroph diversity and activity in landfill cover soils.

Aboveground environment type, soil nutrient content and arbuscular mycorrhizal fungi explain establishment success of Centaurea jacea on ex-arable land and in late-successional grasslands

We studied the relative importance of the aboveground and belowground environment for survival and growth of emerged seedlings of Centaurea jacea to better understand the general difficulty of establishing late-successional species at restoration sites on ex-arable land. Potted seedlings growing on soil from six late-successional grasslands and from six ex-arable (restoration) sites were reciprocally exchanged, and survival and relative growth rate of the seedlings monitored. In addition, we assessed aboveground herbivory and colonization of roots by arbuscular myccorhizal fungi of all plants, as well as nutrient availability, and microbial biomass and community composition using PLFA techniques in all twelve soils. Seedling survival was higher in restoration habitat and soil than in grassland habitat and soil, but growth did not differ between the aboveground and belowground environment types. Shoot growth rate was initially correlated with soil nutrient content, and later in the experiment with mycorrhizal colonization levels. Our results indicate that arbuscular mycorhizal fungi may be important for the successful establishment of C. jacea and that abiotic soil factors, like K availability and N:P ratio, can promote mycorrhizal colonization. Hence, the belowground environment should be considered when selecting sites for restoring species-rich grasslands.

Soil properties associated with organic matter-mediated suppression of bean root rot in field soil amended with fresh and composted paper mill residuals

The ability of an organic amendment to suppress soil-borne disease is mediated by the complex interactions between biotic and abiotic soil factors. Various microbiological and physicochemical soil properties were measured in field soils with histories of receiving 4 or 5 years of spring additions of paper mill residuals (PMR), PMR composted alone (PMRC), PMR composted with bark (PMRB), or no amendment under a conventionally managed vegetable crop rotation. The objectives of this study were to (i) determine the residual and re-amendment effects of the organic materials on root rot disease severity; (ii) determine the influence of amendment type on the structure of bacterial communities associated with snap bean roots grown in these soils; and (iii) quantify the relative contributions of microbiological and physicochemical properties to root rot suppression in the field and greenhouse. While all amendment types significantly suppressed root rot disease compared to non-amended soils in both environments, only soils amended with PMR or PMRB sustained suppressive conditions 1 year after the most recent amendment event. Disease severity was inversely related to microbial activity (fluorescein diacetate assay) in recently amended soils only. Terminal restriction fragment length polymorphism (T-RFLP) analysis of the 16s rRNA gene was performed to obtain bacterial profiles. Principal component analysis (PCA) of terminal restriction fragments (TRFs) revealed general differences in bacterial community composition (PC1) among amendment types, and specific TRFs contributed to these differences. Correlation and multiple regression analyses of the measured soil variables revealed that the composition of root-associated bacterial communities and the amount of particulate organic matter—carbon in bulk soils imparted independent and relatively equal contributions to the variation in disease severity documented in the field and greenhouse. Together, our findings provide evidence that disease suppression induced by annual PMR inputs was mediated by their differential effects on bacterial communities and the amount and quality of organic matter in these soils.

Response of Strawberry Black Root Rot to Abiotic and Biotic Soil Factors

Black root rot is a strawberry disease caused by a community of soil-dwelling organisms including Rhizoctonia fragariae, Pratylenchus penetrans, and Pythium spp. Abiotic soil conditions such as texture, organic matter, temperature, and nutrients impact the development and severity of this disease, as do biotic soil characteristics including the presence of nematodes and fungi. A better understanding of how these abiotic and biotic soil factors influence black root rot is necessitated by the phase-out of methyl bromide, which has traditionally been the primary tool for controlling this disease. Numerous studies contribute to our knowledge of black root rot, and these investigations are supplemented by information from related plant systems and pathogens.

The relationship between lime chlorosis, trace elements and Mundulla Yellows

MundullaYellows (MY) is a dieback disorder of Eucalyptus and other native Australian plants in the south-east of South Australia. Recent attempts to find a causal biotic agent have failed. The history of trace element deficiencies in the area and recent work suggest that a strong association of MY with abiotic soil factors is likely. Because lime chlorosis and trace element deficiencies are involved, the MY situation is complicated to explain. This paper attempts to clarify the situation and explain why the symptoms of MY are actually the symptoms of a lime-induced chlorosis.