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published in a memorandum (A.R.C. 10011) dated 27th April, 1948, which was extensively used by both the Drainage League and the Drainage Board in support of the various submissions made by them. The conclusions are as follows : (a) Sewage sludge has a moderate manurial value as a source of slowly available nitrogen and phosphate. It provides very little potash. In general, the crop-producing power of sludge taken from drying-beds is much less than that of an equal weight of farmyard manure. The physical effects of sewage sludge on the soil are less pronounced and of a different kind from those of farmyard manure because sewage sludge lacks the coarse fibrous ingredients derived from straw and other plant residues. (b) Only sludges in a comparatively dry state (less than about 50 per cent, moisture) are- convenient for transport and spreading. As they must be applied at heavy rates and are sometimes difficult and unpleasant to distribute, their use must depend on economic and local considerations so that no general statement can be made on their agricultural value. (c) Digestion improves the physical condition of sludge and the availability of its nitrogen. These improvements are still more evident when the digested sludges are shed-dried and pulverized. (d) Certain sludges from sewages of industrial origin contain metallic and other wastes which may render their phosphate unavailable and may sometimes be harmful to crops in heavy dressings. Such sludges and also those to which iron salts have been added in the course of treatment at the sewage works should be tested on a small scale before they are used extensively. (e) Satisfactory rotting of straw takes place in compost heaps prepared with about one and a half parts of sludge dry matter to one part of straw, provided the heap is satisfactorily wetted and aerated. Field trials have shown that such composts are better than sewage sludge alone because they supply some potash and have better physical effects on the land. Although composts of sludge and straw have proved somewhat inferior to equal quantities of farmyard manure in field trials, they provide convenient methods of adding bulky organic manures to market garden soils. Only a limited number of field experiments have been carried out on composts of sewage sludge and town refuse ; some of these have given useful results. (/) No instance is known in which the use of sewage sludge as a manure for a crop for human consumption has led to an outbreak of typhoid or dysentery infection, but special precautions should be taken in using sludge for salad and other crops to be eaten raw. Wet sewage sludges should never be used for such crops, and sewage sludges from drying-beds only when they can be applied to the land some months before these crops are to be sown. (4) It will also be useful to refer to a manual entitled " The Utilization, of Sewage Sludge as Fertilizer " which was published in the year 1916 by the Federation of Sewage Works Associations of the United States. In this manual the use of sewage sludge in many places in the United States under many different climati.c and economic conditions is reviewed, and its conclusions regarding the properties of the different kinds of sludge may be conveniently summarized as follows : (a) Raw primary sludge is not usually used because (i) it is odorous, (ii) it has. a higher grease content than digested or activated sludge, (iii) it causes soil acidity, (iv) it may contain toxic substances from trade wastes, and (v) it is a potential carrier of pathogenic bacteria. {b) Liquid digested sludge is seldom used in the United States and only occasionally in England. (c) " Dewatered " digested sludge (i) has less bulk, (ii) can be applied more easily at required rates, (iii) has a minimum of odour, (iv) has a better appearance, (v) can be more easily stored, (vi) has a reduced bacteriological content with less risk of transmitting disease, (vii). has a reduced (by digestion) grease content, and (viii) is humified during digestion. i(d) The drying of digested sludge by heat is rarely attempted because of the low content of plant-food which results. .(e) Heat-dried activated sludge is the best type for agricultural use, whether used by itself or mixed with other fertilizer, because (i) it has greatly reduced bulk, (ii) it can be applied easily, especially when pulverized, (iii) it has a minimum odour, (iv) it contains more nitrogen than digested sludge, (v) it can be applied as top-dressing, (vi) it has a grease content which is greatly reduced by digestion, and (vii) it is believed to be free from harmful bacteria.

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