The Potash Development Association (PDA) is an independent organisation formed in 1984 to provide technical information and advice in the UK on soil fertility, plant nutrition and fertilizer use with particular emphasis on potash. See also www.pda.org.uk.

Note: Hardcopies of PDA’s publications are available only in the UK and Ireland.

Soil Analysis: Key to Nutrient Management. Revised November 2011. Comprehensive guide to soil sampling and interpretation of soil results including indispensable reference material not found in any other single source. Download a pdf file from the PDA website.

Balanced Nutrition Shown by Nitrogen: Sulphur Ratios. November 2011. The majority of the N and S in crops (other than the Brassicae, such as oilseed rape, cabbage, kale etc) is in combination in proteins, and as with most animal proteins the ratio of N to S (N:S) in plants is fairly consistently around 12:1. Read more on the PDA website.