and their attention was thus attracted to the manurial problems to which this deficiency gives rise. Many of these problems were of local interest but that of nitrogen deficiency was found to be common to all provinces. The work done at Pusa and Cawnpore demonstrated the very considerable loss of nitrates by drainage during periods of heavy rainfall, and the deductions drawn from the records of the drain gauges maintained there were amply confirmed by quantitative estimates made in the field under very varied conditions of cultivation, cropping, manuring and rainfall. For several well defined tracts, it is now possible to state the conditions which must be satisfied if the loss due to this and other causes is to be reduced to a minimum, but further research is necessary before generalisations applicable to India as a whole can be formulated. The work of recent investigators at Pusa and Nagpur points to the conclusion that the gains and losses of nitrates from Indian soils may be very much greater than those occurring in temperate climates. At Pusa, for example, losses of 60 to 150 lbs. of nitric nitrogen per acre per annum may occur on cultivated fallow land, the actual loss varying with the soil and character of the monsoon. At Nagpur, a loss of as much as 160 lbs. of nitric nitrogen per acre per annum has been recorded from unirrigated black cotton soil. In comparison with the quantities lost through drainage and denitrification, the amounts of nitrate removed from soils by most crops are very small.

Although but little of the nitrogen removed is returned to the soil in the form of manure, there is no definite evidence that the cropping values of Indian soils are diminishing. That they are maintained at a low but stable level of fertility as a result of the large annual increments of nitrogen which accrue from natural recuperative processes in the soil has been established by work done in all provinces, and quantitative estimates of these increments have been made in Bombay, the Central Provinces and the Punjab. It has also been established that these increments. vary widely owing to the operation of causes which have not as yet been clearly defined. Further research in this direction is urgently required to determine with greater precision the causes involved and to enable practical measures for accelerating the natural recuperative processes. under varying conditions of soil and rainfall to be devised. Many phases of the problem are of a biological character but the lack of suitably trained research workers has prevented the biological aspect from receiving the attention it deserves. In particular, little work has hitherto been done on the recuperative processes in the extensive areas in which rice is grown under swamp conditions and in which the agricultural conditions and practices differ in a very marked degree from those obtaining in the rest of India.

The low humus content of Indian soils is, to some extent, due to the fact that organic manures are so little used. Its primary cause is, however, the very rapid decomposition of the organic matter in the soil which takes place in tropical and sub-tropical conditions and which makes it difficult to maintain a sufficiently high proportion cf humus. The experiments with various forms of organic manures which have been carried out by the agricultural departments have shown that the amount