June 1908.J 



549 



SCIENTIFIC AGRICULTURE. 



THE LOSS OF WATER PROM SOIL 

 DURING DRY WEATHER. 



On this important subject Dr. Leather, 

 Imperial Agricultural (Jnemiso in India, 

 has recently published a paper (Mem. 

 Dpi. Agri. iud., Ghein. Series I. 6. Feb. 

 1908). He begins by pointing ouo that 

 the ordinary explanation or movement 

 oJf water in the soil by simple capilaricy 

 is insufficient. If it begins to dry off 

 from tne top it will only move up from 

 the next particles at first, then from 

 others, and so on. 



The general conclusions to which he 

 comes from his experiments are that 

 during a dry period water moves up- 

 wards from a limited depth only, which 

 ac Fusa (rlengal) was about 3 feet ; thac 

 water evaporates at a rate depending on 

 tne amount of water present, the rate of 

 loss being much greater immediately 

 after rain than subsequently.— [Ed.] 



MEMORANDUM ON ALKALI AND 

 WATER-LOGGING IN IRRI- 

 GATED LANDS. 



By R. W. Smith. 



The general question of drainage in 

 cultivated laudo is one which, receives 

 attention, as a ride, only wnen it be- 

 comes an absolute necessiuy. Deep gra- 

 velly soils, wiiere cultivation is carried 

 on witn tne assistance of natural rain- 

 fall only, present no difficulties in tnis 

 respect. With a heavy retentive clay 

 sub-soil the case is different, and tne 

 water-plane, or '"surface of saturation, ' 

 approacnes more or less that of tne 

 ground surface. 



2. I believe it is a generally accepted 

 fact that witn a saturation of tne soil 

 approacmng i>U per cent, all ordinary 

 piant grow tii (leaving out of tne question 

 aquatic plants) is arrested, and if rhis 

 condition is continued, ordinary plants 

 cannot live. 



8. There are two distinct evils produced 

 by defective drainage, and tnese are 

 olten mistaken one lor the other. They 

 are (1) water-logging ; (2) alkali. The 

 tormer is by lar the most common, and 

 this is fortunate, as in ruaay cases it only 

 requires a little observation and coni- 

 monsense to minimize or remove the 

 evil. This is exactly the case in irrigated 

 Jahds, because the water supply is or 



ought to be under control. It is not so 

 with water-logged pasture lands in 

 Europe, for instauce, as the over-satur- 

 ation is brought about by excessive rain- 

 fall combined with impervious sub-soil, 

 both of which elements are beyond the 

 control of the cultivator. The result is 

 that the natural feeding grasses are 

 swamped out and have to give place to 

 others, such as rushes, sedge, &c., which 

 are useless. 



4. As about two-thirds of the area of 

 Ceylon are dependent mainly or alto- 

 gether on artificial water supplies in the 

 form of irrigation, it is generally easy to 

 avoid water-logging. The remedy is 

 simple. Turn less water on to the lands, 

 and none at all from artificial sources 

 when it is raining. The latter would 

 seem to be an obviously unnecessary 

 piece of advice, but it is nevertheless 

 needed in many cases. 



5. To those who live in the regions of 

 tropical rains, it may not appear remark- 

 able that natural lakes are seldom, if 

 ever, seen. The overllow of the heavy 

 Hood waters has had the effect of scour- 

 ing away the outlets of the natural 

 depressions where lakes might have form- 

 ed, and turn these depressions into 

 continuous valleys, each with its stream 

 beds or water-course. In a very few flat 

 places near the sea coast some natural 

 depressions or " villus " are found, taking 

 the form of, say, shallow lakes or swamps. 

 In these cases the water- plane has come 

 to the surface all round the perimeter of 

 the depressions. If an artificial water 

 supply, say an irrigative tank or channel, 

 is situated near the " villu," the surplus 

 waters— there ought not to be any— 

 from the field supplies find their way, 

 partly on the surface, partly below it to 

 the " villu," and the natural result is 

 that the water-plane is raised still higher 

 and more land becomes over-saturated 

 "or vvater-logged " and will not grow 

 crops. If the ordinary cultivator would 

 read the lesson very clearly taught by 

 this, he would see that he must not over- 

 step the margin which mai-ks the limits 

 of sufficient water supply and water- 

 logging. The only remedy for the case 

 of such lands as are thus unfortunately 

 situated in these natural depressions is 

 to be found inartificial drainage outlets- 

 and then it becomes a question as to 

 whether the lands are worth the cost. 

 The remedy for the partially water- 

 logged land situated between the •'villu" 

 and the higher ground is to be found in 

 not allowing surplus waters to fiow on 

 to them, 



