Question 1

In a soil at pH 5.0, most of the inorganic P is likely to be in the form of _______.

Accepted Answer

At a pH of 5.0, soil conditions are acidic, which favors the formation of hydrous iron and aluminum phosphates. These forms of phosphorus are more soluble in acidic conditions compared to others like calcium phosphates, which are more stable in neutral to alkaline soils.

Question 2

Non-point source losses of which element are considered to be a serious water pollution problem because the resulting high concentration of the element in stream water is toxic to most fish.

Accepted Answer

D

Question 3

In acid soils the principal chemical form of phosphorus available for plant uptake is ____.

Accepted Answer

In acid soils, the principal chemical form of phosphorus available for plant uptake is H₂PO₄⁻.

Question 4

The total phosphorus lost from various watersheds is most closely correlated with _____.

Accepted Answer

High soil erosion is the most closely correlated with the total phosphorus lost from various watersheds because it leads to the loss of soil particles, which can carry phosphorus away from the watershed.

Question 5

The nutrient most often limiting the growth of aquatic plants and algae in unpolluted fresh water lakes is ______.

Accepted Answer

Phosphorus (P) is the nutrient most often limiting the growth of aquatic plants and algae in unpolluted fresh water lakes. This is because P is often the scarcest nutrient in freshwater ecosystems and is required for biological processes such as photosynthesis and growth. When P is added to a lake through human activities such as fertilizer runoff or sewage, it can cause eutrophication and algal blooms.

Question 6

Other things being equal, a soil with 30% clay of the ____ type would be expected to have the greatest potassium -fixing capacity.

Accepted Answer

2:1 type clays, due to their structure and high surface area, have a greater capacity to fix potassium compared to other types listed. This is because the 2:1 clay minerals, such as montmorillonite, have layers that can trap potassium ions between them.

Question 7

Compared to the same soil used for cropland, a forested soil would be expected to lose _____ total P to streams draining the watershed.

Accepted Answer

Forested soils tend to have lower erosion rates and greater soil organic matter content, which can help to retain phosphorus in the soil. Therefore, a forested soil would be expected to lose less total P to streams compared to a cropland soil.

Question 8

Other things being equal, a soil with 30% clay of the ____ type would be expected to have the greatest phosphorus -fixing capacity.

Accepted Answer

Allophanic soils have a high phosphorus-fixing capacity due to their unique structure and high surface area, which allows them to adsorb and hold onto phosphorus more effectively than other soil types.

Question 9

The amount of P lost from agricultural soils by the process(s) of _____ is generally considerably greater than the corresponding losses of potassium.

Accepted Answer

The answer of The amount of P lost from agricultural...

Question 10

In various parts of the world, soil phosphorus is associated with which of the following environmental problems?

Accepted Answer

Soil phosphorus depletion and eutrophication of lakes can both be caused by excessive use of phosphorus fertilizers, which can lead to runoff of phosphorus into waterways. Toxic levels of phosphate in groundwater can also occur due to this runoff, contributing to a variety of environmental problems.

Question 11

Loss of P to groundwater is likely to be most significant for which type of soil?

Accepted Answer

Cultivated organic peat soils are highly susceptible to P loss to groundwater because they have a high organic matter content and are typically drained for agricultural purposes, which can lead to increased leaching of nutrients like P.

Question 12

In acid soils the principal chemical form of potassium available for plant uptake is ____.

Accepted Answer

In acid soils, potassium ions (K+) are adsorbed to clay and organic matter particles, and are held there by electrostatic forces. The adsorption process produces negatively charged sites on the surface of the clay particles, which attract the positively charged potassium ions. Thus, the principal chemical form of potassium available for plant uptake in acid soils is K+ ion adsorbed to negatively charged soil particles, which is represented by the chemical formula K⁺.

Question 13

Mycorrhizae improve the nutrition of many plants by ______.

Accepted Answer

Mycorrhizae form a mutualistic relationship with plants in which they extend the root system and increase the surface area for absorption of nutrients, including phosphorus. They also release enzymes that break down organic matter, releasing nutrients like phosphorus, which they transport to the plant root.

Question 14

In most soils, mineralization of soil organic matter is an important source of plant available ____.

Accepted Answer

The answer of In most soils, mineralization of soil organic...

Question 15

If a manager can afford only a limited amount of soluble P fertilizer for a calcareous soil with low phosphorus availability, the best plant growth is likely to be obtained if the P fertilizer is applied _____.

Accepted Answer

Applying P fertilizer in narrow bands or localized concentrations allows for more efficient use by the plant since the fertilizer is placed directly in the root zone. This is especially important in calcareous soils with low phosphorus availability, where the P fertilizer may quickly become fixed and unavailable for plants. Applying evenly across the entire area or in combination with ground limestone may not be as effective in increasing plant growth in these types of soils.

Question 16

Compared to land that is not disturbed by tillage, conventionally plowed cropland usually loses much more ______.

Accepted Answer

Conventionally plowed cropland disrupts the soil structure and increases erosion, leading to greater loss of both particulate and dissolved phosphorus, resulting in higher levels of total phosphorus in waterways.

Question 17

Approximately what percentage of the P in surface soils is typically found in organic forms?

Accepted Answer

In surface soils, a significant portion of phosphorus (P) is found in organic forms, typically ranging from 25 to 75%. This is because organic matter in the soil, such as plant residues and microbial biomass, contains phosphorus that is essential for various biological processes.

Question 18

The sites in certain clay minerals which fix potassium ions are also capable of fixing which other ion?

Accepted Answer

The sites in certain clay minerals which fix potassium ions are also capable of fixing ammonium ions (NH4+), which has the same charge as potassium ions (K+). Option B represents ammonium ions.

Question 19

In what range of soil pH is phosphorus generally most available to plants?

Accepted Answer

Phosphorous is generally most available to plants in a pH range of 5.5-7.0. At extremely low pH levels (below 4.5), phosphorus becomes less available due to the abundance of H+ ions competing for binding sites. At higher pH levels (above 7.0), phosphorus ions can combine with calcium ions to form insoluble compounds, making it less available to plants.

Question 20

Application of phosphorus fertilizer usually makes plants more susceptible to diseases.

Accepted Answer

Phosphorus is essential for plant health and development, and when used appropriately, it can help plants become more resistant to diseases by strengthening their root systems and improving overall vitality.

Quiz 14: Soil Phosphorus and Potassium