December, 1908.] 



563 



SCIENTIFIC AGRICULTURE. 



CONSERVATION OP SOIL 

 MOISTURE. 



To no country is the question of the 

 conservation of soil moisture more im- 

 portant than to India, where there are 

 large tracts of country on which the 

 crops are often limited in growth by the 

 inadequate supply of water available in 

 the soil. An article on the subject 

 which Mr. D. Milne, Economic Botanist 

 in the Punjab, contributes to the Agri- 

 cultural Journal of India, therefore, 

 should be read by all those interested 

 in the development of Scientific Agri- 

 culture in this country. There are 

 many cases, as Mr. Milne points out, 

 where the alert farmer might by skilful 

 farming in this direction reap a better 

 crop than his more careless neighbour. 

 It is well known that a soil on which 

 plants are growing loses much more 

 water by evaporation than does a bare 

 soil, and that on bare land which is 

 fairly firmly consolidated right to the 

 surface more moisture will be eventually 

 lost by evaporation thau on laud the 

 surface of which has been well pulverised 

 and kept stirred to the depth of a few 

 inches. Two things, therefore, are of 

 prime importance— to keep the land 

 rigorously clear of weeds and to 

 pulverise the surface of the soil simul- 

 taneously with the ploughing of the 

 land. There is a third way, to which 

 Mr. Milne refers, of conserving soil 

 moisture, which is often practised in 

 other countries— the process knoAvn as 

 "mulching." This consists in spreading 

 some fairly open or porous material such 

 as refuse litter, inferior grass, straw or 

 leaves, or other organic substance in a 

 thin layer over the surface of the land, 

 the idea being to form a layer of matter 

 which will retain a considerable volume 

 of air in the spaces between its com- 

 ponent particles and so retard the swift 

 exchange of the dry air of the atmo- 

 sphere for the more or less moist air that 

 is in contact with the soil surface. But 

 " mulching," though useful, is difficult 

 to carry out on large areas. Mr. Milne 

 discusses at length also the question of 

 the character of the implements used in 

 tillage operations in relation to the 

 conseivation of soil moisture, and seems 

 to think those in use in Europe have the 

 advantage in this respect. —Indian Agri- 

 culturist, October 1, 1908. 



NOTE ON A TOXIC SUBSTANCE 

 EXCRETED BY THE ROOTS OP 

 PLANTS. 



By P. Fletcher, m.a., b.sc, 



Deputy Director of Agriculture, Bombay 

 Presidency. 



It has more than once been suggested 

 that plants, like animals, excrete (from 

 their roots) material that is no longer of 

 use to them or that are bye-products of 

 the process of metabolism, and that such 

 substances are injurious to the kinds of 

 vegetation by which they are excreted. 

 Brugmans was apparently the first to 

 suggest this, and it has, at various 

 times, been affirmed by Plenk, Humbolt, 

 Cotta, De Candolle and others, denied 

 by Hedwier. Braconnot, Walser, Bous- 

 singgault, Unger, Meyen and others, and 

 has for long been considered as non- 

 existent except with regard to carbon 

 dioxide and possibly an acid phosphate 

 and formates. 



Again, Dr. Gyde (Trans-Highland and 

 Agricultural Society, 1845-47, pp. 273-92) 

 in water cultures obtained, on evaporat- 

 ing the residual liquid, a very small 

 amount of yellowish or brown substance, 

 or portion of which was organic in 

 character. He concluded that the 

 amount excreted was very small, and 

 that the substance was not injurious to 

 the plants that gave rise to it. 



From observations on crops growing 

 in the field, the writer some years ago 

 (while in Egypt) came to the conclusion 

 that certain phenomena could only be 

 explained on the theory of excretion. 

 This was especially the case with cotton 

 crops in which a grass was allowed to 

 grow as a Aveed. The cotton, grown 

 under irrigation, did not revive on appli- 

 cation of more water ; its poor state was 

 therefore not due to lack of moisture in 

 the soil. Manures likewise seemed to 

 have comparatively little effect towards 

 improvement ; appropriation by the 

 weed of food material was therefore not 

 the cause of the poor growth. Aeration 

 had as little effect as manure. 



Observations in the field were resumed 

 in India, and these tended to very 

 materially strengthen the view that 

 materials injurious to other crops were 

 excreted by the roots of certain common 

 crops in India ; this was especially the 

 case with sorghum. The system of 

 mixed crops very prevalent in the, un- 



