Phosphate leaching
I understand why phosphate leaching from the soil is seldom a problem but can't seem to find when it would become a problem. Any hints?
OK, here is a hint: Phosphate leaching does not commonly occur because of the phosphate fixation. Phosphate fixation is caused by either Fe& Al (in acidic soils), Ca (in alkaline soils) or silicate clays (in neutral pH soils). So, can you think of a soil type (mentioned in this course) that does not have either Fe, Al, Ca, and silicate clay minerals. In that soil type, phosphate leaching can be an issue especially if phosphate fertilizers are applied in large quantities (which on its own can lead to phosphate leaching)
is the answer is none? is there any soil other than those 3 types?
thank you
no, there is a soil type (actually the whole soil order) in which phosphate leaching will happen, since that soil does not have silicate clay minerals (or any other mineral particles) nor Fe/Al or Ca ions........ Do not think about soil pH, but what causes phosphate fixation....
Regosolic order?..
Also, soil that has abundant negative charges, like montmorillonite will repel anion like phosphate, which will lead to phosphate leaching. Am I correct?...
Thank you.
Sorry, but no. It is not a Regosol. Regosol being a mineral soil could potentially have Fe/Al or Ca ions which all contribute to phosphate fixation
I'm confused... Is it organtic soil?
And also at the review session you mentioned that soil that's has abundance of negative charge will also lead to phosphate leaching.. Or did I hear it wrong?
Thank you.
Yes, it is Organic soil, since in Organic soil there is a very limited (or no) amount of either Fe, Al, and Ca ions that are all responsible for phosphate fixation. Organic soil also has a very limited (or no) amount of silicate clay minerals. In addition, Organic soil tend to have a large number of negative charges (organic matter has pH-dependent charge, and Organic soils tend to have very acidic pH due to various organic acids being released in their limited decomposition), which in turn leads to electrostatic repulsion of phosphate anions, keeping them in soil solution and making them susceptible to leaching.