Thirty-eight experiments were made on commercial farms to determine the fertilizer requirement of sugar beet grown with farmyard manure (F.Y.M.). They were in two groups; the first (1961–3), with uniformly applied F.Y.M., tested the value of additional fertilizer—nitrogen, phosphate and potash, with and without agricultural salt (crude sodium chloride). The second (1964–7) tested the value of fertilizer N and agricultural salt with and without F.Y.M.

The average economic optimum dressings of fertilizers with F.Y.M. were 0·6 cwt/acre N, 0·3 cwt/acre P2O5, 0·5 cwt/acre K2O, with agricultural salt which largely replaced the need for potash. Chemical analyses of samples of F.Y.M. used in the second group of experiments gave no reliable guide to the requirement of additional nitrogen or sodium. With adequate P2O5 and K2O, the F.Y.M. increased sugar yield at all except one site, on average equivalent to the increase from 0·3 cwt/acre N. Agricultural salt increased yield economically at most sites except on the silts round the Humber and the Wash. No clear relationship was found between soil analysis for sodium and sugar yield response to agricultural salt, but where the exchangeable soil sodium was less than 25 ppm Na, a response was likely.