87 REPORT II.

riELI) EXPEEIMENTS IN THE KHAETOUM DISTEICT.

ERIC SLATER, Farm Manager.

The Central Research Farm is situated on the right bank of the main Nile two miles north of the junction of the Blue and White Niles, and comprises in all 230 feddans of irrigable land. In conformation and soil characters it is fairly representative of the narrow belt of cultivation which extends almost continuously along the river banks through the Khartoum and Berber Provinces. The rainfall throughout this area is negligible, and crops are dependent on artificial irrigation effected by means of the primitive Persian water wheel, or " sakia," and recently in certain districts by modern steam pumps.

Irrigation is facilitated by the e:istence of a flood bank, built up by the river to a higher level than that of the adjacent areas, providing a natural slope inland. An explanation for this almost universal feature is found in the following note from a report by the Government Geologists, Messrs. Grabham and Dunn.* As the stream widens its bed by cutting into one bank, a sand-bank is often formed on the opposite side, and if conditions are suitable, subsequent floods build up this bank until vegetation is able to maintain a footing on it all the year round. As soon as plants get a hold they aid the flood water to deposit silt, which forms a surface soil. The accretion of sand and silt takes place more' rapidly on the river-side edge of the bank, as that is the region where the velocity of the silt laden water of the parent stream is checked. The consequence is that the edge of the alluvium is built up to the level of the highest flood, while a depression is left between it and the original river bank behind.

Demarcation.—The chemical features of the farm soils and their bearing upon the crops grown has been dealt with in another report. The following extracts from Mr. S. C. Dunn's preliminary report on the site will explain the manner in which the farm has been partitioned : The soil of the Central Research Farm may be roughly divided into three parts : (1) The strip adjoining the river bank. This is loamy in nature, patchy in quality, with areas containing marked quantities of salts scattered over it. The soil from the sagia-land on the river bank has been washed over this area causing a difference between the superficial coating of surface soil and the silt subsoil already in situ. Further, this portion has from time to time been built on by natives, and the low mounds representing the sites of their houses have been levelled, thus increasing the probable variety of the surfa-ce soil and adding to the salt content of the whole.

* " Report on the Sennar District."