a1 Reader in Agricultural Chemistry, Assistant Chemist, Agricultural Department, Cambridge University.
Summarising the above comparisons between soil analyses and results of manuring, the following conclusions are arrived at:
That except in extreme cases the determination of the percentages of “total” nitrogen, phosphoric acid, potash, and lime, in a soil does not give reliable indications as to the possibility of improving the pasture by manuring.
That determination of the percentage of phosphoric acid soluble in 1 per cent, citric acid solution does generally give reliable indications as to the probable success of phosphatic manuring, provided that for pasture soils the limit below which “available“ phosphoric acid may be considered as deficient is fixed as high as 0·02 per cent.
That potash manuring is suggested as likely to give distinct results if the soil contains not more than 0·01 per cent, of potash soluble in 1 per cent, citric acid solution.
That liming is not indicated as likely to be profitable unless the soil contains certainly less than 0·25 per cent, of chalk.