Soil structure formation through the action of plants

Chapter 6 Water relations and water management of vertisols

Pioneer plant Phalaris arundinacea and earthworms promote initial soil structure formation despite strong alluvial dynamics in a semi-controlled field experiment

The role of biology in the formation, stabilization and degradation of soil structure

Introduction Legumes are very important source of protein after cereals. These plants are capable of biological nitrogen fixation and increasing soil fertility as cover crop or including in crop rotation and reducing soil erosion which improve sustainable agriculture. Increasing use of chemical fertilizer which has negative effect on soil structure which cause unbalance on physical and chemical propertied of soil which ultimately reduce nutrient element absorption. Nowadays due to environmental problems use of biological fertilizers are good substitutions. On the other hand biological fertilizer use improve soil fertility. Protein quantity and quality are basic nutritional problem. According to use of more than 85000 tones chemical fertilizers in legume cultivation in Iran. It is necessary to conduct correct and efficient inoculation for each legume crop in the country including bean, which is one of the important crop for human consumption. In most cases biological fertilizers are complementary of chemical fertilizers in a sustainable agriculture. The aim of this study was to compare the effect of interaction effect of mycorrhiza vesicular, Psodomonas bacteria and humic acid on yield and yield components of bean. Material & Methods Mycorrhiza inoculation was prepared in soil science Lab in Tabriz University in sterile sandy loam. Bacterial inoculation Pseudomonas putida prepared in soil biology of Tabriz University. Humic acid extraction was done with method of Kay et al., (2004). For Seed bean Phaseolus vulgaris variety Cos-16 from agronomy and plant breeding department of Tabriz University which is resistant to drought. Soils for this experiment were collected from Khalat Poshan research station from 0 to 25 cm depth and passed through 4mm sieve after sun sterile method. Soil physical and chemical properties were estimated with standard methods. Each pot was filled with three kilogram sterile soil. Seventy gram of mycorrhiza inoculation was spread in 5 cm of top soil and then bacteria inoculation was added to soil just below the seeds. Humic acid extracted from vermicompost and applied to soil in the powder form in three levels, control (H0), 200 mg kg-1(H1), and 400 mg kg-1 (H2). Pots were place in green house at 25C. After treatment application 5 seeds were sown in each pots and pot moisture kept at 0.9 FC. Pots were irrigated with distilled water whenever needed. After 4 months plant roots and shoot properties and plant yield and yield components were estimated. This experiment was conducted in the form of factorial on the base of complete randomize block design in Tarbiat Moalem University of Tabriz. First and second factor were in two levels, control and applied for mycorrhiza (M0 and M1) and bacteria P. putida (S0 and S1) and humic acid in three levels control (H0), 200 mg kg-1 (H1) and 400 mg kg-1 (H2) in three replications. Data analysis was done with MSTATC and SPSS and mean comparison were done with LSD test for significance and figures drown with Excel 2007. Results & Discussion Analysis of variance of data for plant height showed that interaction effects of humic acid and bacteria were significant at 1% level and mycorrhiza was significant at 5% level. Mean comparison of results showed that least plant height mean from interaction of humic acid and bacteria with S0H1 treatment with (28.58 cm) and the highest was (30.35cm) with S1H1 treatment. Analysis of variance showed that main effect of mycorrhiza were significant at 1% level and interaction effect of humic acid and bacteria at 5% level on shoot wet weight of bean. Analysis of variance for main effect of humic acid and mycorrhiza were significant at 1% level for shoot dry weight and main effect of bacteria and interaction effect of bacteria and mycorrhiza were significant at 5% level for shoot dry weight of bean. Analysis of variance showed that main effect of mycorrhiza and humic acid were significant at 1% level and interaction effect of mycorrhiza and humic acid at 5% level on root dry weight. Analysis of variance of Mycorrhiza and bacteria main effect on ratio of root dry weight to shoot were significant at 1% level and main effect of humic acid and interaction effect of humic acid and mycorrhiza were significant at 5% level. Analysis of variance showed that main effect of mycorrhiza and humic acid were significant at 1% level and main effect of bacteria and interaction effect of mycorrhiza and bacteria were significant at 5% level for seed numbers of bean. Analysis of variance showed that main effect of bacteria and mycorrhiza and interaction effect of bacteria and mycorrhiza were significant at 1% level and interaction effect of bacteria and mycorrhiza were significant at 5% level on stem length. Analysis of variance showed that main effect of humic acid and mycorrhiza were significant at 1% level and main effect of bacteria and interaction effect of humic acid and bacteria were significant at 5% level for stem diameter. Analysis of variance showed the main effect of mycorrhiza was significant at 1% level and main effect of humic acid and interaction effect of bacteria and mycorrhiza and interaction effect of bacteria and humic acid and main effect of humic acid were significant at 5% level for the seed yield. Conclusion Analysis of variance of experiment treatments in this research showed that treatment applied had positive effect on agronomic properties of bean and humic acid could have direct and positive effect on plant root and shoot growth.

Kerman and its surrounding towns consist of a flat alluvial plain of fine silt and clay materials. In morphological aspects, these sediments have a very gentle slope with the main infrastructure of the city build on them. Generally, the structure of undisturbed soils is developed over time due to the influence of environmental factors. Geological factors in Kerman fine-grained alluviums have caused the formation of some structures after their deposition. In this research, in order to investigate soil structure and determine the collapsibility index, 40 samples were collected from different parts of the city. Next, the engineering properties of Kerman’s soil (e.g., mineralogy and collapsibility), development of soil structure, and the sensitivity of soil structure were studied. To determine sensitivity and structural coefficient of these soils, Schmertmann’s criteria (1969) and Liu and Carter’s model (2000) were applied, respectively. Moreover, scanning electron microscopy (SEM) images and energy-dispersive X-ray spectroscopy (EDS) method were used to study Kerman deposits. Mineralogy results of Kerman plain soils reveal that there are minerals such as illite, chlorite, smectite, and calcite in these deposits. The SEM images confirmed the consolidated and compressed structure of soil grains in most of the samples. Furthermore, other results show that soils of Kerman are often compressed and over-consolidated. Collapsibility index shows a quite direct relationship with structure development, as collapsibility is low in the samples with low destructuring coefficient while it is high in the samples that have a structure.

Soil invertebrates play a significant role in improving soil structures. Man uses nitrogenous fertilizers to improve growth of cultivated lands and provide plants with nutrients. The intensive addition of fertilizers accumulates soil nitrate which affects soil fauna. This investigation was designed to study the effects of nitrate concentration in the soil and some ecological factors on the soil macroinvertebrates inhabiting different agricultural lands at El-Minia governorate. Six sites were chosen for this study. Samples of soil and invertebrates were collected monthly during a period of one year extended from December 2013 till November 2014 using pitfall traps. The study revealed the occurrence of twenty six taxa in the investigated sites. The density of each taxon obviously varied in each site according to the season. The majority of collected macroinvertebrates assigned to phylum Arthropoda. The most dominant species at all sites belonged to order Isopoda then Orthoptera. Higher density of macroinvertebrates was recorded during spring and summer compared to their relevant numbers during winter and autumn. All collected macroinvertebrates exhibited negative correlation with nitrate concentration of soil in their habitat, especially isopods that showed strong significant correlation.

Studying and modeling the effects of soil properties and management on soil structure and near saturation water retention is vital for the development of effective soil and water conservation practices. The contribution of soil intrinsic properties and extrinsic conditions to structure stability was inferred, in quantitative terms, from changes in water retention curves near saturation (low matric potential, 0-50 cm, macropores > 60 µm) that were obtained by the high energy moisture characteristic (HEMC) method. The S-shaped water retention curves were characterized by the modified van Genuchten model that provided: (i) the model parameters α and n, which represent the location of the inflection point and the steepness of the water retention curve, respectively; and (ii) the soil structure index, SI=VDP/MS, where VDP is the volume of drainable pores, and MS is the modal suction. Model parameters, claculated by the soil-HEMC model, were related to soil properties and hence soil water retention properties were linked to measured characteristics in several field and laboratory experiments. Soil SI increased exponentially with the increase in α and the decrease in n, while the relationship between SI and α/n was linear. An improved description of the water retention and its link to pore and apparent aggregate size distribution, by using the model parameters α and n, could potentially assist in the selection of management practices for obtaining the most suitable type of soil structure depending on the desired soil function.

We present a mechanistic, spatially and temporally explicit microscale model to investigate the interactions between a growing root, its exudates and the soil structure. Our model allows us to simultaneously simulate and study the dynamic rearrangement of soil particles, the input and turnover of organic matter, the root growth and decay, as well as the deposition, redistribution and decomposition of mucilage into the rhizosphere. The interactions between these components are realized within a cellular automaton framework. Mechanistic rules lead to the formation and break-up of soil structures. The most stable configuration is determined by the amount and attractivity of surface contacts between the particles. Alteration of surface types due to addition and decomposition of organic matter and the root growth induced movements of particles result in varying aggregation dynamics over time and space.We illustrate the capability of our model by simulating the growth and shrinkage period of a fine root in a two-dimensional, horizontal cross section through the soil. We evaluate various scenarios to identify the impact of the root and further influencing factors that shape soil aggregation in the rhizosphere. More precisely, we address how the soil structure formation is influenced by soil texture and the amount of mucilage. We quantify the variations in local porosity due to the change in available pore space as influenced by the root growth. We further identify attractive properties of the soil surface induced by root exudation as key factors for the creation of stable soil structures.

Soil functions are closely related to the structure of soil microaggregates. Yet, the mechanisms controlling the establishment of soil structure are diverse and partly unknown. Hence, the understanding of soil processes and functions requires the connection of the concepts on the formation and consolidation of soil structural elements across scales that are hard to observe experimentally. At the bottom level, the dynamics of microaggregate development and restructuring build the basis for transport phenomena at the continuum scale. By modeling the interactions of specific minerals and/or organic matter, we aim to identify the mechanisms that control the evolution of structure and establishment of stationary aggregate properties. We present a mechanistic framework based on a cellular automaton model to simulate the interplay between the prototypic building units of soil microaggregates quartz, goethite, and illite subject to attractive and repulsive electrostatic interaction forces. The resulting structures are quantified by morphological measures. We investigated shielding effects due to charge neutralisation and the aggregate growth rate in response to the net system charge. We found that the fraction as well as the size of the interacting oppositely charged constituents control the size, shape, and amount of occurring aggregates. Furthermore, the concentration in terms of the liquid solid ratio has been shown to increase the aggregation rate. We further adopt the model for an assessment of the temporal evolution of aggregate formation due to successive formation of particle dimers at early stages in comparison to higher order aggregates at later stages. With that we show the effect of composition, charge, size ratio, time and concentration on microaggregate formation by the application of a mechanistic model which also provides predictions for soil aggregation behaviour in case an observation is inhibited by experimental limitations.

Products of biological processes are the dominant factor of soil structure formation in A horizons, while in B horizons their role is less expressed. Soil structure influences dominantly the structural domain of the pore system in bimodal soils thus affecting soil hydraulic functions. The form of soil hydraulic functions depends upon the pore size distribution and generally upon configuration of the soil pore system. We used the functions derived for the lognormal pore size distribution and modified them to bi-modal soils. The derived equations were tested by experimental data of catalogued soils. The procedure leads to the separation of two mutually different domains of structural and matrix pores. The value of the pressure head (potential) separating the two domains is not constant and varies in a broad range. For each domain we obtained its water retention function and unsaturated hydraulic conductivity function. The separation of hydraulic functions for the two domains is a key problem in the solution of preferential flow and in controlling lateral flow between the structural and matrix domains. Water retention function is fully physically based while the conductivity function still keeps fitting parameters, too. Their simple relationship to tortuosity and pores connectivity was not confirmed. Since they differ substantially for matrix and structural domains, we suppose that there exists a great difference in configuration of porous systems in structural and matrix domains. The use of uniform fitting conductivity parameters for the whole range of pores is not justifiable.

Soil is one of the most valuable of common goods. It provides essential ecosystem services including food, nutrient and water cycling, waste treatment, carbon sequestration and greenhouse gas regulation to support plant and human life. However, soils around the world are severely degraded with immense costs to human wellbeing. Addition of organic amendments, in the form of natural organic matter, to soil may allow us to simultaneously improve soil carbon, recycle and replenish nutrients, improve structure, retain water and increase plant productivity. To achieve these improvements, it is necessary to understand the regulation of organic matter transformation. The main aim of this thesis is to examine the chemical and biotic interactions in the transformation of organic inputs in agricultural soils and the impacts of these organic amendments on them. This aim is addressed by examining the interaction between soil carbon, nitrogen and phosphorus cycling and soil microbiota, which play a major role in determining the transformation of organic matter. The findings of the two main experiments are summarised below. The knowledge developed will contribute to managing aagroecosystems for the supply of multiple benefits to the wellbeing of society and agricultural sustainability. The first experiment focuses on examining the effects of organic input stabilisation via composting or pyrolysis on its transformation by soil biota. The key findings from this experiment are (i) soil microbial composition changes with organic amendment but (ii) overall stoichiometric invariance provides a mechanistic framework for understanding the transformation of organic amendment, and (iii) carbon composition strongly influences microbial community composition and soil functions. Results from this experiment are presented in two chapters. The second experiment builds on the first experiment by increasing the ecosystem complexity using a terrestrial model ecosystem to better reflect the soil ecosystem in nature. It seeks to determine the interaction between altered rainfall (drying and rewetting) and organic input. In the context of global change, the bigger question asked was, “Does organic input improve the resistance and resilience of a grassland ecosystem to altered rainfall?” The key findings from this experiment are (i) grassland soil microbial communities are generally resistant and resilient to fluctuations in rainfall regardless of compost amendment, and (ii) these properties of the soil microbial community were translated to resilience but not resistance in soil functions, (iii) Plant growth responses were sensitive to rainfall and compost amendment, but interaction effects were rarely detected. Finally, in terms of elemental stock content, (iv) compost amendment increased soil carbon, nitrogen and phosphorus stocks regardless of rainfall regimes but, (v) these subtle improvements can only be detected by careful consideration of depths in the soil profile. Results from this experiment are presented in two chapters. These results supply further weight to the argument that it is necessary to take multiple measures and examine interactions to effectively determine the impact of organic amendments on soil community structure and function, particularly in a world experiencing rapid global change.

Water repellency of sieve fractions from sandy soils and relationships with organic material and soil structure

The prevailing paradigm is that recovery of post-fire soil-hydrologic properties is dominated by pedogenic processes that drive soil structure formation, a critical process for regaining soil hydrologic functioning. The primary drivers for soil structure formation are climate and vegetation required for soil biological activity. Evidence shows that following perturbations of agricultural soils (e.g., compaction) or abrupt land use change soil structure recovery may take years to decades. In contrast, measurements from post-fire soils show that recovery of critical soil hydrologic properties (notably soil saturated hydraulic conductivity) is rapid (generally within 1 to 3 yrs) and occur at rates faster than expected from soil structure regeneration. To reconcile the rapid post-fire recovery rates, we propose a new conceptual framework for recovery of post-fire soil-hydrologic properties driven primarily by accelerated erosion of the unstable and structureless pyrolyzed surface soil layer. In this framework, initial recovery occurs not by redeveloping new structure in the pyrolyzed surface soil layer, but rather by removing it, thus exposing minimally-affected sublayers as new soil surfaces. Based on wildfire characteristics, a typical depth of pyrolyzed soil layer is estimated to be a few centimeters (

Chapter 10 - Effects of Compaction on Soil Biota and Soil Biological Processes

Soils are fundamental to preservation and sustainability of life- support system on Earth. Soils develop as the most dynamic and complex interface linking atmosphere,hydrosphere,lithosphere and biosphere. Soils harbor enormous diversities of microbial communities as the primary driving forces for global exchanges of matter and energy on our planet. Despite of its profound importance,the invisible soil microbes have for long been underappreciated. In the early 2000s,there has been growing awareness that soil microbiology has attracted huge interest from nonsoil scientists due to the introduction of three-domain phylogeny. It is also known as tree of life theory which is widely recognized as the most accurate reflection of the relatedness of all organisms and provides us with a tool to classify and elucidate the largely untapped resource of soil microbial communities. In January 2005,the Department of Earth Sciences of National Natural Science Foundation of China organized a workshop of ‘Soil Biology and Soil Processes’ with focused discussion on soil microbiology research frontiers. The workshop outlined research priorities,cross-disciplinary research opportunities,technological needs and potential breakthroughs within soil microbiology. This workshop has witnessed the rapid advances of soil microbiology in soil nutrient transformation,global environmental changes and environmental remediation over the last decade in China. This article will give a brief review on soil microbial researches in the past decade in China,present the status quo of funding system and highlight the challenge and opportunities for future soil microbiology in China.