Exam 14: Soil Phosphorus and Potassium

For soils with significant pH dependent charge, raising the pH with limestone tends to increase the availability of potassium in the soil.

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

Annual plants deficient in P usually flower and mature more rapidly than P-sufficient plants.

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

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 _____.

Deep rooted vegetation such as forest trees can increase the available potassium content of surface soil horizons even though no potassium is added to the soil profile.

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

For optimum growth of herbaceous plants such as cassava, corn, and lettuce, a concentration of at least 1.0 mg/L P should be dissolved in the soil solution.

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

In a soil with a very low potential buffering capacity, the most efficient approach to using potassium fertilizer would be to apply frequent small doses rather than a single large dose.

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

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

During the last several decades, modern agriculture in the industrialized countries has tended to deplete cropland soils of their supply of available P.

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

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

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

The term, eutrophication, comes from the Greek word meaning "to suffocate" and connotes anaerobic decomposition in soils.

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

Water running off from a bare field whose soil had an EPC of 0.1 mg/L would be expected to be lower in P concentration than runoff from a field whose soil had an EPC of 2 mg/L.

For an unfertilized temperate region forested soil with a large amount of interlayer fixed potassium, but a low amount of readily available potassium, the level of readily available potassium is expected to be higher in early spring than in late fall.