New research is under way to check whether the current advice for maintaining phosphorus soil indices at two is applicable across all soil types.

The advice was based on research carried out by Rothamsted Research on only two soil types, explained Stuart Knight, director of crops and agronomy for NIAB TAG.

“But is that right for all soil types? And if you don’t, what level of yield loss do you get, and how often?” he asked.

The new four-year project would be trying to answer those two questions across a combinable crop rotation on six soil types ranging from heavy clay to sandy loams and shallow soils over chalk.

“With started with sites that are low in P, and then created a range of soil P indices on those fields using the same system as Rothamsted, which is involved in the project, did in the original research. The aim will be to find out what level of soil P is sub-optimal, and how often it limits yield.”