sooby said:" ...
The clay minerals generally have a negative charge so they would attract the positively charged ions (cations). That's why nitrogen in nitrate form tends to leach more (negative charge) than ammonium nitrogen (positive charge). The major cations would be potassium, calcium, magnesium and sodium. Phosphorus has a negative charge as does sulfur. The micronutrients are a mix of positive and negative.
Good point, Sue. Clay is probably only a good buffer for
negatively positively charged plant nutrients. {Edited to change "negatively" to "positively"}
As to pH, clay mostly reflects what has been in solution around it recently. You can make it more acid or more basic.
But as a buffer, it RESISTS pH CHANGE much more than sandy soils. That might be partly the huge surface area of clay: its particles are just 1-5 microns in diameter, so they're "all surface area" compared to sand or even silt. Solid particles that don't dissolve only contribute to chemistry what's on their surface. A bag of big rocks has very little surface area on those rocks, compared to a bag of sand or a bag of clay.
So when a New Englander limes his soil with Dolomite lime, he lays it on pretty thick since he has rather acid, very clayey soil. If someone with sandy soil had acid soil (perhaps from acid rain), she would use around 1/8th as much lime as a clay-bound gardener would. Clay is a string pH buffer. Sand has almost no buffering.
