The salts of the soil, when in excess, are chlorides and sulphates of soda: the carbonates are present in very small quantities indeed.
The following selection from a paper by Mr. Lang Anderson in the December 1903 number of the Journal of the Khedivial Agricultural Society is interesting.
“Voelcker’s analyses of the two samples of soil taken from the drained bed of what was Lake Edku near Alexandria give the following results:—
| No. 1. | No. 2. | ||
|---|---|---|---|
| Oxide of iron | 11·69 | 11·04 | |
| Iron pyrites | 0·08 | 0·11 | |
| Aluminium | 6·36 | 10·88 | |
| Lime | 2·08 | 7·73 | |
| Magnesia | 1·79 | 0·93 | |
| Soda | 0·79 | .. | |
| Sodium chloride | 8·11 | 8·56 | |
| Potash | 0·65 | 1·23 | |
| Sulphuric acid | 2·23 | 2·56 | |
| Carbonic acid | 0·19 | 4·75 | |
| Phosphoric acid | 0·16 | 0·19 | |
| Insoluble silicates and sand | 62·23 | 45·81 | |
| Organic matter | 3·64 | 6·21 | |
| Total | 100·00 | 100·00 | |
| Containing nitrogene | 0·035 | 0·070 | |
| „ ammonia | 0·042 | 0·079 | ” |
28. Basin irrigation.
—Considering the times of flood and low supply, the climate of Egypt, the turbidity of the Nile flood, and the deltaic formation of the Nile valley, no better system than basin irrigation as practiced in Egypt could possibly have been devised. If the flood had come in April and May and been followed by a burning summer, or if the actual autumn floods had been followed by the frozen winters of Europe or the warm winters of the Sudan, basin irrigation would have been a failure or a very moderate success; but, given the Egyptian climate, basin irrigation has stood without a rival for 7000 years.
Basin irrigation, as it has been practised in Egypt for thousands of years, is the most efficacious method of utilising existing means of irrigation which the world has witnessed. It can be started by the sparsest of populations. It will support in wealth a multitude of people. King Menes made his first dyke when the Egyptian nation was in its infancy. Egypt, in Roman times, supported a population twice as dense as that of to-day. The direct labour of cultivation is reduced to an absolute minimum.
Shakespeare’s genius has crystallised the system for all time:—
“They take the flow o’ the Nile
By certain scales in the Pyramid; they know,
By the height, the lowness, or the mean, if dearth
Or foizon follow: the higher Nilus swells,
The more it promises: as it ebbs, the seedsman
Upon the slime and ooze scatters his grain,
And shortly comes to harvest.”
If we cast back our view to the dawn of Egyptian history, we can picture the Nile Valley as consisting of arid plains, sand dunes, and marshy jungles, with reclaimed enclosures on all the highest lands. Every eight or ten years the valley was swept by a mighty inundation. The seeds of future success lay in the resolve of King Menes’ engineers to confine their attention to one bank of the river alone. It was the left bank of the river which history tells us was first reclaimed. A longitudinal dyke was run parallel to the stream, and cross dykes tied it to the Lybian hills. Into these basins or compartments the turbid waters of the flood were led by natural water-courses and artificial canals and allowed to deposit their rich mud and thoroughly saturate the soil; and meantime the whole of the right bank and the trough of the river itself were allowed to be swept by the floods. It must have been on this wild eastern bank that were conducted all the hippopotamus hunts which are crowded on the wall pictures of buildings of the early dynasties. In all probability, the first six dynasties contented themselves with developing the left bank of the Nile. As, however, the population increased, and with it the demand for new lands, it became necessary to reclaim the right bank of the river as well. The task now was doubly difficult, as the river had to be confined to its own trough. This masterful feat was performed by the great Pharaohs of the XIIth Dynasty, the Amenemhats and the Usartsens, who, under the name of Sesostris, usurped the place of Menes in the imagination of the ancient world. They were too well advised to content themselves with repeating on the right bank what Menes had done on the left. By suddenly confining the river they would have exposed the low-lying lands of Memphis and Lower Egypt to disastrous inundations. To obviate this, they widened and deepened the natural channel which led to the Fayoum depression in the Lybian hills, and converted it into a powerful escape to carry off the excess waters of high floods; and so successful were they in their undertakings that the conversion of the Fayoum depression into Lake Mœris was long considered by the ancient world as one of its greatest wonders. They led the flood into the depression when it was dangerously high, and provided for its return to the river when the inundation had come to an end. By this means, they insured the lake against being at a high level during a period of flood. The gigantic dykes of entry and exit were only cut in times of emergency, and were reconstructed again at an expense of labour which even an Egyptian Pharaoh considered excessive. To understand how capable Lake Mœris was to control the floods, and turn a dangerous into a beneficial inundation, I should recommend a study of Sir Hanbury Brown’s “Fayoum and Lake Mœris.” As years rolled on the Nile widened and deepened its own trough, to which it was now confined; and, eventually, the time came when Lake Mœris could be dispensed with without danger. It was gradually reclaimed and converted into the Fayoum with its 350,000 acres of cultivated land.