The paper describes the results of over 300 factorial experiments carried out in each factory area in the years 1934–49 for the Sugar Beet Research and Education Committee of the Ministry of Agriculture as a result of co-operation between Rothamsted workers and the agriculturists and fieldmen attached to the beet factories. All the experiments tested the effects of levels of nitrogen, phosphate and potash, and rather more than half tested the effect of salt also.Except on fen soils, nitrogen gave substantial responses in all factory areas, especially in the presence of high levels of potash or salt. Large variations in response from season to season were closely associated with the rainfall of the preceding winter months, responses being greater after wet winters than dry ones.In spite of some selection of sites in favour of greater responses, the average net returns from phosphate were relatively small.The effect of potash was closely linked with the amount of nitrogen applied; in the presence of nitrogen, dressings well above the level of 1·2 cwt. K2O per acre tested in the experiments are likely to give a useful net return. Soils derived from the Chalky Boulder Clay seem to be exceptional in showing no response. Apart from this, there were only small variations in responses to nitrogen and potash between factory areas. The application of 5 cwt. salt gave substantial responses in almost all parts of the country, whether or not potash was also applied; on the other hand, responses to potash were usually small when salt was also applied.Whilst there was a general relationship between soil analysis for phosphate and potash (citric acid method) and crop response, adjustments to the optimal dressings according to soil analysis were not of sufficient reliability to be of much practical value.

Modern field experiments on the manorial values of sewage sludges began in the 1930's when Cranfield (1939) tested local sludges at centres in the Midlands, and Rothamsted Experimental Station (1938) had a factorial series of trials testing fermented town refuse and its interactions with fertilizer nutrients. This work was greatly stimulated by the wartime shortage of fertilizers and an elaborate series of field experiments was initiated at Rothamsted in 1940.Various types of sewage sludge, straw composts and town refuses were tested, and their interactions with fertilizers were examined on a range of crops andsoils. A brief report on this work, with a summary of the results then available, was made for the Ministry of Agriculture (Agricultural Research Council, 1948) and the detailed results of 100 of the full-scale experiments done on commercial farms has been published (Bunting, 1963). A simplified series testing similar organic materials on microplots, chiefly at rural schools, has also been reported (Garner, 1962). The parent experiment at Rothamsted was larger and lasted longer than any of the others; it also contained features, such as the inclusion of different farmyard manures made under standard conditions, and the assessment of residual effects, that could not be repeated elsewhere. This paper records some of the agricultural results of this experiment. EXPERIMENTAL Description of the experiments and the manures testedThe experiments were done yearly on different fields from 1940 to 1949 at Rothamsted on heavy loam that had carried a long sequence of arable crops. The manures were applied to potatoes in the first year, and the succeeding cereal crop measured residual effects. The chief organic manures tested were: 8 kinds of farmyard manure (FYM) made under controlled conditions, sewage sludge from 7 sources, sludge-straw composts from 4 sources, 5 types of town refuse, cut bracken stacked over winter, and peat.A 5 x 5 lattice square design tested 11 materials each at single and double rates, and 3 controls without organic manure. These 25 main plots were repeated in 3 blocks and each was divided into 4 subplots to test fertilizer N, P and K in all combinations, confounding the 3-factor interaction. There were therefore 300 subplots in each experiment. The rates of dressing at the single level were: (a) Farmyard manure: 8 tons per acre for fresh material made with 8 lb. of litter per beast per day; the other manures were applied in amounts corresponding to the quantity of feeding stuffs used to make the 8 tons of fresh FYM. Details of making the experimental manures are given later.(6) Sewage sludges supplying 5 tons of dry matter per acre.(c) Town refuses, sludge-straw composts, and rotted bracken at 8 tons/acre.(d) Peat at 2 tons/acre. The fertilizers tested supplied: 0-6 cwt. N per acre as ammonium sulphate; 0-6 cwt. P 2 O 6 per acre as superphosphate; 1-0 cwt. K 2 O per acre as muriate of potash. In 1940 and 1947 phosphate was not tested, but a basal dressing of superphosphate supplying 0-6 cwt. ...

Several town-refuse manures were compared with farmyard manure at Rothamsted and five other places between 1940 and 1947. The organic manures were used at 8 and 16 tons/acre with and without fertilizer nitrogen and potash. Direct and residual effects were measured on agricultural and horticultural crops.All organic manures improved yields in the year of application, FYM most and consistently. The average percentage increases in yield produced by the pulverized refuses tested, in relation to the increase from an equal weight of FYM, were: sugar beet 22, mangolds 83, carrots, 85, potatoes 51. The corresponding figures for screened dust were: sugar beet 40, mangolds 28, carrots 41; the dust slightly depressed potato yields. Averaging all sixteen experiments on root crops, the pulverized refuses had 64% of the first-year effect of FYM and the screened dust 25%.

Field experiments of modern design that included carrots were first made at Woburn in 1934, to compare the value of nitrogen in dried poultry manure with ammonium sulphate. The experiments were repeated at several centres and continued until 1939. Most other crops responded well to nitrogen but in only one of the five experiments containing carrots did ammonium sulphate at 3 cwt/acre increase the root yield, and in two it significantly depressed yield. Ammonium sulphate tended to lessen plant numbers, but it increased the yield of tops (Rothamsted Experimental Station, 1934)

Barley was grown on plots which had carried potatoes in the 26 years prior to 1901, and which had received no fertilizer since that date. Ammonium sulphate was applied during the war years, and yields of SO bushels per acre were obtained from plots which had received superphosphate or dung annually for many years before 1901, Control plots, which had not received superphosphate when potatoes were being grown, gave yields of 20–25 bushels per acre. Barley can thus benefit from the residual effect of phosphates in certain types of soil, after a lapse of nearly 50 years.