Amber Anderson

Learning Objectives
  • Identify major pieces within the phosphorus cycle and factors impacting plant availability
  • Explain potential impacts on the environment from contrasting management
  • Recommend practices to decrease the environmental impact of phosphorus fertilization

Phosphorus Characteristics in Soil

There is a small amount of phosphorus in the soil solution and, therefore available to a plant at any point in time. Low total amounts in the soil and low solubility mean that the plant can lack sufficient phosphorus for growth, particularly in cool and wet spring conditions when Iowa’s annual crops have a minimal root system exhibiting lots of branching.   Availability can be impacted by soil pH, at both low or high ranges, as phosphorus can form calcium phosphates or iron phosphates. Due to low plant availability, mycorrhizal associations can be significant contributors to plant uptake for phosphorus.

Phosphorus fertilizers include animal manures, DAP (Diammonium phosphate) or MAP (monoammonium phosphate) are made by combining ammonia and phosphoric acid. Alternatively, mined rock phosphate or other unique materials such as guano.

Role in Plant Growth

As a part of ATP, phosphorus is important for energy transfer within the plant. Therefore, stunted plants are expected, but purple coloring is also common.

Corn plants in a light colored soil with most of the outer portion of the leaves purple.
Photo credit: Lizzie Dykstra
3 corn plants on a black surface. The top plant is small with purple and green colors. The middle plant is slightly bigger but still depicting purple discoloration. The bottom plant is the biggest and mostly green with only a small amount of purple at the base near the roots.
The top plant is from the center of a disturbed area (pipeline construction), the edge of disturbed area, and just outside of the disturbed area on the bottom. Photo credit: Lizzie Dykstra.

Phosphorus Loss

Phosphorus loss from Iowa soils or to Iowa water bodies is generally attributed to erosion of the entire soil rather than via water. Therefore, strategies to decrease loss or improve water quality focus on decreasing erosion rather than biological mechanisms for nitrate loss. Decreasing erosion, through decreasing tillage, increasing cover, buffer strips, increasing perennial cover on the landscape, decrease phosphorus loss to water bodies.

Additionally, livestock manure can be detrimental to local water quality, resulting in decreased use and function as can be seen in the photo below. Stream exclusion fencing, keeping livestock from wallowing in the water and adding manure, can decrease the risk to water quality. Application of manure should be incorporated, not applied to frozen ground when it would be more likely to run off, and should be set back from the stream or water body.


Importance in Water Bodies

Significant water quality issues result from phosphorus enrichment, both at local and national scales. Nutrient contribution from the upper midwest contributes to the significant hypoxic or ‘dead zone’ in the US Gulf of Mexico. Eutrophication, or the nutrient enrichment of these water bodies causes excessive growth, and then excessive decomposition, which decreases oxygen in the water. Since organisms in the water need oxygen, this causes a collapse in the local ecosystem. Therefore, it is important to minimize loss from our soils and decrease impact on nearby water bodies.

Nutrient Reduction Strategy
Key Takeaways

Phosphorus is limiting in many environments and must be carefully managed to ensure successful plants and environmental quality.


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Introduction to Soil Science Copyright © 2023 by Amber Anderson is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.