Why the MLSN project has a minimum soil pH of 5.5

Below a soil pH of 5.5, soluble aluminum can rapidly increase. That soluble aluminum can be toxic to roots. Soil microbial activity, and consequently the decomposition of thatch, can also be inhibited at low soil pH. Those are the two reasons the MLSN calculations are made for a set of soil samples with soil pH (1:1 dilution with deionized water) greater than 5.5. The image at right shows both of these effects, in an unlimed plot at the Park Grass…