Soil Science 2

This statement is true because all substances, including water, tend to move from areas of higher energy to areas of lower energy. This movement is driven by the principle of entropy, which states that systems tend to become more disordered over time. In the case of water, it will naturally flow from areas where there is a higher concentration or energy level to areas where there is a lower concentration or energy level until equilibrium is reached. This process is commonly observed in various natural phenomena, such as diffusion and osmosis.

Clay is the correct answer because it has the ability to form longer ribbons compared to sand and silt. In texture by feel methods, the texture of soil is determined by feeling the soil and observing its characteristics. Clay particles are very small and have a high level of cohesion, allowing them to stick together and form longer ribbons when moistened. Sand and silt particles, on the other hand, are larger and less cohesive, resulting in shorter ribbons. Therefore, clay is the component that accounts for longer ribbon formation in this method.

Clay can hold more water at the saturation point compared to the other options. This is because clay particles are very small and have a high surface area, allowing them to attract and hold more water molecules. Additionally, clay has a high water holding capacity due to its ability to retain water through capillary action. Therefore, clay is able to retain more water and reach a higher saturation point than well-structured sand, poorly structured sand, and silt.

Sand particles are larger in size compared to silt and clay particles. This larger particle size creates larger pore spaces within the soil, allowing for better air movement and drainage. As a result, sand improves the aeration quality of the soil by facilitating the exchange of gases between the soil and the atmosphere.

Clay particles are known to behave as colloids, which means that they have a tendency to remain suspended in water without settling out. Unlike silt and sand particles, which are larger and heavier, clay particles have a smaller size and exhibit cohesive properties that allow them to remain dispersed in water for longer periods of time. This behavior is due to the unique structure and composition of clay particles, which contribute to their colloidal nature.

Granular soil structure is typically found in surface soil (A horizons). This structure is characterized by small, rounded aggregates that easily crumble and have a loose, crumbly texture. It allows for good drainage and aeration, making it ideal for plant growth. Columnar, sub-angular blocky, prismatic, and platy soil structures are typically found in deeper soil layers and have different characteristics than granular structure.

The given statement suggests that the particle in question falls within a specific size range according to the USDA. This particle is neither as fine as clay nor as coarse as sand. Therefore, the correct answer is silt.

The Munsell color system is a scientific method used to describe soil colors. It uses a combination of hue, value, and chroma to assign a specific color designation to a soil sample. The color designation is given in the format of a hue, such as 10YR, followed by a value, such as 3, and a chroma, such as 4. This system allows for consistent and standardized communication of soil colors among scientists and researchers.

Clay is the correct answer because it is the textural element that plays a crucial role in soil aggregation. Clay particles have a small size and a high surface area, which allows them to bind together and form aggregates. These aggregates improve soil structure by creating pore spaces for water and air movement, promoting root growth, and enhancing nutrient availability. Clay also has a high cation exchange capacity, which helps to retain essential nutrients in the soil. Therefore, clay is the most important textural element in soil aggregation.

The question asks for a textural class that is not included in the given options. The options provided are silt, loam, sand, sandy silt, and clay. The correct answer, sandy silt, is not one of the textural classes.

Gravimetric determinations give a direct measurement of the water content in soil. This method involves collecting soil samples, drying them in an oven to remove all moisture, and then weighing the samples to determine the amount of water lost. This provides an accurate measurement of the water content in the soil. Tensiometers measure soil moisture indirectly by measuring the tension or pressure exerted by the water in the soil. Gypsum blocks measure soil moisture based on the electrical resistance of the soil, while neutron scattering measures soil moisture by measuring the amount of neutrons that are reflected back.

The forces of cohesion and adhesion in water are largely a result of hydrogen bonding. Hydrogen bonding occurs when the positively charged hydrogen atom of one water molecule is attracted to the negatively charged oxygen atom of another water molecule. This bonding creates strong intermolecular forces, which contribute to the unique properties of water such as high surface tension, capillary action, and its ability to dissolve many substances.

When a dry soil high in clay content is moistened, it has the ability to absorb water and expand. This expansion exerts significant force, which can cause pavements and building foundations to crack. Clay particles have a unique structure that allows them to hold water and increase in volume when hydrated. This property of clay makes it highly expansive and a potential cause of damage to infrastructure when present in high amounts in the soil.

Capillarity in soils involves both adhesion and cohesion. Adhesion refers to the attraction of water molecules to the soil particles, while cohesion refers to the attraction between water molecules themselves. These two forces work together to allow water to move upwards through small spaces in the soil, against the force of gravity. The symmetrical nature of the water molecule enhances capillarity, but it is not the sole factor responsible for it. The matric potential in soils does affect capillarity, as it is related to the size of the capillary pores in the soil. Capillarity also plays a role in unsaturated water movement in soils, as it helps water to move through the soil matrix. Water uptake from soils by plants also involves capillarity.

The USDA considers this particle to be between .05mm and 2mm. The only option within this range is sand. Clay particles are smaller than .05mm, while silt particles are between .05mm and .002mm. Therefore, sand is the correct answer.

Dull gray colors are characterized by low chromas. Chroma refers to the intensity or purity of a color, and low chromas indicate that the color is less vibrant or intense. Dull gray colors have a muted or subdued appearance, lacking strong saturation or vividness.

Soil tilth refers to the physical suitability of a soil or plant growth. It refers to the overall condition and quality of the soil, including its texture, structure, porosity, and moisture-holding capacity. A soil with good tilth is loose, well-drained, and crumbly, allowing roots to penetrate easily and facilitating the movement of air, water, and nutrients. This is important for healthy plant growth and root development. Soil tilth is influenced by factors such as organic matter content, soil compaction, and management practices.

Silt is described as feeling smooth or flourlike. It is a sedimentary material with particles that are larger than clay but smaller than sand. Silt particles have a fine texture, giving it a smooth feel when touched. This characteristic sets it apart from clay, which has a sticky and plastic feel, and from sand, which has a gritty and coarse feel. Therefore, silt is the correct answer based on its description.

The hue 10YR is the yellowest because it has the highest proportion of yellow color compared to the other options. The number 10 indicates that it is closer to yellow on the color wheel, while the letters YR suggest a slight shift towards red. The higher the number, the more yellow the hue is, making 10YR the yellowest option among the given choices.

Gravimetric determinations involve measuring the weight of a soil sample before and after drying it in an oven. This method directly measures the water content of the soil by determining the loss in weight due to evaporation of water. Tensiometers, neutron scattering, and gypsum blocks are indirect methods that measure soil water potential or electrical conductivity, which are related to soil water content but not a direct measurement. Therefore, gravimetric determinations provide a direct measurement of soil water content.

Sodium adsorption does not promote aggregation because it is a process where sodium ions are attracted to and held onto the surfaces of soil particles, preventing them from coming together and forming aggregates. In contrast, wet-dry and freeze-thaw cycles can cause soil particles to expand and contract, promoting the formation of aggregates. Organic secretions, such as root exudates, can also contribute to aggregation by acting as a binding agent.

Clouds have the shortest average residence time among the given sources of water. This is because clouds are constantly moving and changing, with water vapor condensing and forming droplets that eventually fall as precipitation. The residence time of water in clouds is relatively short compared to other sources, such as oceans and ice caps, soil moisture, and groundwater, which can retain water for longer periods.

Fungal hyphae have an important influence on soil structure because they stabilize macro aggregates. Fungal hyphae penetrate through the soil, binding soil particles together and forming larger aggregates. These macro aggregates improve soil structure by increasing stability, reducing erosion, and enhancing water infiltration and retention. This allows for better root penetration, nutrient availability, and overall soil health.

A friable soil refers to a soil that is easily crumbled or broken apart. On the other hand, indurated soil refers to a soil that is hardened or compacted. These two terms are opposite in meaning, so it can be concluded that a friable soil is less likely to be indurated. Therefore, the given answer "False" is correct.

During the process of aerobic respiration, glucose is broken down in the presence of oxygen to produce energy, carbon dioxide, and water. Carbon dioxide is released as a waste product during this process and is a significant source of this gas.

The correct answer is "Prismatic structure may be well developed." Prismatic structure refers to the arrangement of soil particles in the shape of columns, which creates large pores and allows for better water movement and drainage. This structure is often found in clay-rich soils and contributes to their permeability despite the high clay content.

The height of the rise of water in a capillary tube is inversely proportional to the tube radius. This means that as the radius of the tube decreases, the height of the rise of water increases. This is because a smaller radius creates a greater surface tension, which pulls the water up the tube. Conversely, a larger radius reduces the surface tension, resulting in a lower height of water rise.

Drip irrigation is the most efficient irrigation system that produces the most biomass per unit of water applied. In this system, water is directly delivered to the plant roots through a network of tubes or pipes, minimizing water loss due to evaporation or runoff. This targeted approach ensures that plants receive the necessary amount of water without wastage. As a result, drip irrigation maximizes water efficiency and promotes the growth of plants, leading to higher biomass production compared to other irrigation systems.

A chroma greater than 4 does not necessarily indicate a soil in good tilth. Chroma refers to the intensity or purity of color in the soil, specifically in relation to its hue. While a higher chroma value may suggest a more vibrant or intense color, it does not directly correlate with the quality or health of the soil. Good tilth is determined by factors such as soil structure, organic matter content, and nutrient availability, which cannot be solely determined by chroma. Therefore, the statement is false.

To change the texture of a silt loam soil to meet the specifications for a loam, adding sand to the soil and mixing it well would be the most likely solution. Sand is added to increase the drainage and improve the soil structure, making it less compact and more suitable for plant growth. Mixing it well ensures that the sand is evenly distributed throughout the soil, creating a more balanced texture. Clay, compost, and humus may also be beneficial for soil improvement, but in this case, adding sand is the most appropriate choice.

Flocculation is the process in which clay particles combine together to form larger aggregates. This is caused by the interaction between polyvalent cations (ions with multiple positive charges) and the clay platelets. The polyvalent cations neutralize the negative charges on the clay particles, allowing them to come closer and stick together. This interaction is responsible for the flocculation process.

A water molecule is a polar molecule, meaning it has a positive side (the hydrogen atoms) and a negative side (the oxygen atom). This polarity arises due to the difference in electronegativity between oxygen and hydrogen atoms. Oxygen is more electronegative, attracting the shared electrons more strongly, creating a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. This polarity allows water molecules to form hydrogen bonds with other water molecules and interact with other polar substances.

The presence of macropores in the soil enhances the likelihood of polluting groundwater with pesticides and plant nutrients. Macropores are large openings or channels in the soil that allow for the movement of water, nutrients, and contaminants. These openings provide a direct pathway for pollutants to reach the groundwater, increasing the risk of contamination.

Removing excess water from the soil would best assure good aeration. When the soil is waterlogged, the spaces between soil particles become filled with water, which displaces air. Adequate aeration is important for the growth and health of plants as it allows for the exchange of gases, such as oxygen and carbon dioxide, between the soil and roots. By removing excess water, the soil can regain its air-filled spaces, promoting better aeration and creating a favorable environment for plant growth.

Diffusion is the process by which gases move from an area of high concentration to an area of low concentration. In the context of soils, gaseous interchange primarily occurs through diffusion. This is because gases in the soil, such as oxygen and carbon dioxide, move through the soil matrix and between soil particles by diffusion. Mass flow refers to the movement of gases through the soil due to pressure gradients, while dissolution in water is the process of gases dissolving in soil water. Respiration is the metabolic process in organisms, not specific to gaseous interchange in soils. Partial pressure of N2 refers to the pressure exerted by nitrogen gas, but it does not explain the process of gaseous interchange in soils.

Nitrogen gas is not a major factor in determining the soil aeration status because it is not directly involved in the oxygen availability in the soil. Soil aeration is primarily influenced by the volume of macropores, which allow for the movement of air and water in the soil. Oxygen is crucial for root respiration and microbial activity, while carbon dioxide and redox potential are also important indicators of soil aeration. Nitrogen gas, on the other hand, is not directly related to the aeration status of the soil.

The question provides information about the average transpiration loss from leaf surfaces in a particular watershed, but it does not provide any information about the evaporation from the soil surface. Therefore, it is impossible to calculate the evaporation from the soil surface based on the given data.

Soil water is held most tightly at soil moisture potentials with lower values of kPa. Therefore, at -3100 kPa, the soil water is held most tightly.

The process of creating more macropores is most apt to encourage good soil aeration. Macropores are large spaces or channels in the soil that allow for the movement of air. These pores provide pathways for oxygen to enter the soil and carbon dioxide to exit, promoting the exchange of gases necessary for root respiration and the overall health of the soil. By increasing the number of macropores, the soil's ability to hold and distribute oxygen is improved, leading to better soil aeration.

The evapotranspiration (ET) from a pine forest is the combined loss of water through both evaporation from the soil surface and transpiration from the leaves. In this case, the evaporation from the soil surface is given as 5 cm. Since the total evapotranspiration is 50 cm, and the evaporation from the soil surface is 5 cm, the remaining loss must be from the leaf surfaces. Therefore, the level of loss from leaf surfaces is 50 cm - 5 cm = 45 cm.

Based on the given percentages of sand and clay, a soil with 45% sand and 20% clay falls within the range of a loam textural class. Loam soils have a balanced mixture of sand, silt, and clay, making them ideal for plant growth as they have good drainage and water-holding capacity. Therefore, the correct answer is loam.

Practices such as adding organic matter and reducing tillage can be expected to most significantly increase the macropores in a soil. Macropores are large pores or openings in the soil that allow for better water infiltration, root penetration, and air exchange. By adding organic matter, the soil structure improves, creating more macropores. Additionally, reducing tillage helps to preserve the natural structure of the soil, preventing compaction and promoting the formation of macropores. This ultimately enhances the soil's ability to hold and drain water, as well as support healthy root growth.

Silt loam soil has the greatest amount of available water because it has a balanced composition of silt, sand, and clay particles. This composition allows for good water retention while still providing adequate drainage. Clay soil may have a high water-holding capacity but can become compacted and poorly drained. Sand, on the other hand, has low water-holding capacity and drains quickly. Poorly structured sand refers to sand that is compacted and has poor drainage, making it less suitable for water retention. Therefore, silt loam soil is the best option for maximum available water.

The color 10YR5/8 would be typical of a well drained, low-organic matter sandy surface soil. The first part of the code, 10YR, indicates the hue, which in this case is a yellowish-red color. The second part, 5, represents the value, which indicates the darkness or lightness of the color. A value of 5 suggests a moderately dark color. The third part, 8, represents the chroma, which indicates the intensity or saturation of the color. A chroma of 8 suggests a relatively high intensity or saturation. Overall, this color code indicates a moderately dark, yellowish-red color with high intensity, which is typical of a well drained, low-organic matter sandy surface soil.

Flood irrigation involves the application of large amounts of water to the entire field, which can lead to excessive water loss through evaporation and runoff. This method is not efficient in terms of water use because it does not target the specific needs of plants and can result in wastage of water. Therefore, the use of flood irrigation for forage crops will not increase the efficiency of water use by plants in an irrigation system.

Soils high in organic matter commonly hold more available water than comparable soils with lower organic matter levels because they have a higher field capacity. This means that they can retain more water in their pore spaces, allowing for better water availability for plants. The organic matter in the soil helps to improve its water-holding capacity by increasing the soil's ability to absorb and retain moisture. This is beneficial for plant growth as it ensures a steady supply of water for the roots.

Higher soil chemoentrophy is not a cause of higher bulk density in deeper soil profiles. Bulk density refers to the mass of dry soil per unit volume, and it is influenced by factors such as compaction, organic matter content, aggregation, and biota. Higher soil chemoentrophy, which refers to the ability of soil microorganisms to obtain energy from chemical reactions, does not directly affect bulk density.

The matric potential of soil water is not influenced appreciably by the force of gravity. Matric potential refers to the energy required to move water through soil due to the attractive forces between water molecules and soil particles. Gravity primarily affects the gravitational potential of water, which is different from the matric potential. Therefore, the force of gravity does not have a significant impact on the matric potential of soil water.

In a uniformly textured sandy loam profile, the movement of soil water through the profile would be most rapid. This is because sandy loam has a relatively high permeability, allowing water to easily pass through it. Additionally, the uniform texture throughout the profile means there are no barriers or variations in soil texture that would impede the downward movement of water. Therefore, water can quickly and easily move through the sandy loam profile, resulting in rapid downward movement of soil water.

Unsaturated water flow occurs on soils that are at field capacity. Field capacity refers to the maximum amount of water that soil can hold against the force of gravity. When soil is at field capacity, it is already saturated, but excess water can still flow through the soil due to the pressure gradient. This unsaturated flow occurs as the water moves from areas of higher pressure to lower pressure within the soil. Therefore, the correct answer is that unsaturated water flow occurs on soils that are at field capacity.