Project properties
Title Help us to improve efficient P fertilization!
Group Soil Chemistry and Chemical Soil Quality
Project type thesis
Credits 36
Supervisor(s) Hendrik Holwerda (PhD student) and Gerwin Koopmans
Examiner(s) Prof. Rob Comans
Contact info Hendrik Holwerda (hendrik.holwerda@wur.nl)
Begin date 2024/09/01
End date 2025/07/01
Description Goal: Acquire a better understanding of the effect of soil physical properties on phosphorus uptake.

Why: Assessing soil P availability for crop growth is currently purely based upon the chemical P availability of soil. This is tested by a wet chemical P extraction called a soil P test (SPT). In current Dutch P fertilization recommendations critical SPT values for optimal crop yields are not specified for soil type. However, in two long term field experiments we found that the required SPT value to get optimal crop yields was three times lower on a calcareous loamy soil than a sandy soil! Assuming the same critical SPT value for each soil type likely leads to unnecessary high P application on some soils but yield limitations on others. A more accurate estimation of the critical SPT value helps to reduce overapplication of non-renewable P fertilizer.
To improve recommendations, we need to determine which soil properties lead to relatively high or low critical SPT values. For the two experiments we used, we suspect that the difference in critical SPT value is caused by soil physical properties that relate to (pore) water holding capacity and tortuosity (real pathway of molecule divided by straight line distance). A better water holding capacity and lower tortuosity may cause a higher P diffusion rate on the loamy soil than on the sandy soil.

What will you do: You will perform a pot experiment with loamy and sandy soil with different soil water contents to test how this affects P limitation to crop growth on both soils. Depending on time and interest you can try standardized experimental procedures to measure P diffusion in soil and link difference to soil properties. Your results can help us to give a clearer idea how to incorporate soil properties in fertilization recommendations.

During your thesis you will be supervised by Hendrik Holwerda (PhD student) and Gerwin Koopmans.

Interested in this topic? Please contact Hendrik Holwerda (hendrik.holwerda@wur.nl).
Used skills Literature research, lab skills, data processing and analysis, scientific writing and reporting, presentation skills
Requirements As a requirement, we ask for 12 credits of SOC/SBL-courses in the form of at least one course from the following list: SBL-21806 Soil Quality, SOC-21306 Soil Pollution and Soil Protection, SOC-40806 Field Training Soil-Vegetation-Atmosphere Interactions, and SOC-33806 Environmental Analytical Techniques. Furthermore, you have completed at least one course from this list: SBL-35306 The Soil Carbon Dilemma, SOC-36306 Biogeochemical Cycles and Climate Change Mitigation, and SOC-34806 Applications in Soil and Water Chemistry.