Soil phosphorus availability and transformations following biosolids applications
Date
2020
Authors
McDaniel, Jacob P., author
Butters, Gregory, advisor
Barbarick, Kenneth, advisor
Davis, Jessica, committee member
Frasier, Marshall, committee member
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Abstract
Land application of biosolids has many benefits such as providing nutrients for plant growth as well as adding organic matter to soil. However, there is the potential for negative impacts due to the high concentration of phosphorus (P) relative to nitrogen (N). Much work has been done looking at the effects of over application of P and best management practices for the application of biosolids in the eastern United States. However, little work has been done in the western United States where the environment is very different due to lower rainfall and higher soil pH and calcium (Ca) concentrations. This study was composed of four parts to help understand how P reacts in the western United States and to look at the implications for plant growth. These parts included: (1) fractionation of P in biosolids, (2) vertical distribution of P following long-term biosolids applications, (3) seasonal soil P cycling, and (4) plant uptake of P. The fractionation of P was designed to look at several biosolids and determine a method to be able to characterize the P that is present. This information would have the potential to aid in decision making about best managing the P from various sources. The vertical distribution of P following long-term application was designed to characterize the P in the soil profile. It is usually assumed that P is not mobile, but over long periods of time and with high application rates it can move. Seasonal changes of the different pools of P were studied to better understand how time of year affects the amount of P available in soil samples, and potentially to plants and the environment. The last study was designed to show how different sources of organic amendments supply different amount of P to a plant. The objective was to be able to better determine the amount of plant available P from an amendment. The results of the different studies begin to show the similarities and differences in the behavior of P in the western United States and in the east. The fractionation study found that the assumptions that are used for manure cannot be applied to all factions of P in biosolids and that a longer shaking time is needed. This study also found that there are differences among wastewater treatment plants that is mostly related to differences in treatment methods in an individual wastewater treatment plant. The vertical distribution of P study found that over time with repeated applications of P in dryland wheat (Triticum aestivum L.)-fallow rotations there is a significant effect on occluded P. Even with repeated applications most of the accumulations of P were limited to the plow layer and in a system where P chemistry is dominated by Ca, Fe still plays an important role. The seasonal change in the fractions of soil P study showed the changes in soil P were greatly affected by soil properties, water availability, climate, and application rates of biosolids. The high concentration of Ca in the soils favored the formation of Ca bound P, and saturated soils affected the forms of Fe bound P. The addition of organic matter and Fe with biosolids applications increased the concentration of soluble P, microbial biomass P, and Fe bound P. The plant uptake study found that there is a much larger effect of the soil on plant uptake than the source of the amendment. There is an inverse relationship between a soil's ability to adsorb P and the concentrations of plant tissue P when the plants are young. As the plants age and develop large root masses they can increase their tissue P concentrations. This work shows that in the western United States there is more of a need to focus on the soils than the biosolids being applied to be able to make the best management decision. All the studies that looked at the P after it had been added to soil found that Ca affects the transformations and uptake of P by plants. In the western United States, there are areas that have large amount of Ca in the soil and areas that do not. As a result, interactions of Ca and P need to be focused on and further studied to ensure adequate plant nutrition as well as being a steward of the environment.
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Subject
phosphorus
biosolids