Scientific Agriculture. 



178 



cotton from such selected plants when ordinary Sea Island was selling for half this 

 price. We are quite aware that such a system of selection is entirely beyond what 

 can be expected in Egypt, but it has been given here to indicate to Egyptian culti- 

 vators what steps are taken not only to keep up, but to improve the staple of Sea 

 Island cotton. If such a system cannot be realised in this country by individual 

 growers it shoidd be put into practise on their behalf, that is to say seed areas should 

 be set apart for the purpose and the grain placed at the disposal of careful cultiva- 

 tors who would in their turn produce seed for general use." — B. (7. African Gazette. 



EFFECT OF PLANT-GROWTH, AND OF MANURES, UPON 

 CARBONATE OF LIME IN THE SOIL. 

 An interesting paper upon the changes which take place in the amount of 

 carbonate of lime (chalk), which are brought about by natural agencies, by manur- 

 ing, and particularly by the growth of plants, has been contributed to the Royal 

 Society's Proceedings by Messrs. A. D. Hall, m.a., and Or. N. H. J. Miller, of the 

 Rothamsted Experiment Station. Since Cavendish discovered that carbonate of 

 lime dissolves in rain-water charged with carbonic acid, and ascertained the 

 presence of bicarbonate of lime in many natural waters, it has been recognised that 

 the carbonate of lime (chalk) present in most soils must be subject to regular loss. 



As the soils of the Rothamsted experimental plots and the drainage waters 

 collected from the plots afford peculiar facilities for the study of this important 

 question, they have naturally formed the foundation of the investigations by the 

 authors. The natural surface soil on the Rothamsted Estate, and in Hertfordshire 

 generally, contains little or no earbouate of lime, but during the eighteenth century 

 and earlier very large quantities we re applied artificially until it formed 5 per cent, 

 or so of the surface soil. The method adopted was to sink pits through the clay to 

 the chalk, which was then lifted and spread in considerable quantities. And the 

 most experienced Hertfordshire farmers agree that chalking of lands so circumstanced 

 is the best mode of culture they are capable of receiving. This carbonate of lime is 

 being gradually dissolved out by the rain water percolating through the soil, anj 

 the loss will amount to about 800 lbs. to 1,000 lbs. per acre per annum. 



The rate of loss is increased by the use of sulphate of ammonia, and is 

 diminished by the use of nitrate of soda or organic debris like farmyard manure. 

 The normal growth of crops tends to restore a certain amount of carbonate of 

 lime and other bases to the soil, because the plant in feeding upon the neutral salts 

 dissolved in the soil water takes more of their acids than of their bases, leaving 

 behind a basic residue combined with carbonic acid excreted from the plant roots. 



With ordinary agricultural and horticultural crops the restoration of bases 

 must be considerable, probably supplying sufficient base for the nitrification process 

 which is always going on. This explains why many soils containing little or no 

 carbonate of lime (chalk) remain healthy under ordinary cultivation, provided that 

 acid manures like sulphate of ammonia or superphosphate (especially the lower 

 grades) are not used on them. 



These researches also explain one or two other points which have been 

 observed in connection with the use of nit rate of soda as a manure. It has long been 

 noticed that the continued use of nitrate of soda is very destructive to the texture 

 of a clay soil, intensifying all the clay properties, rendering the soil persistently 

 unworkable when wet, and forming hard and intractable clods when dry. The 

 ultimate cause of such an effect is the " deflocculation" of the fine particles compo- 

 sing the soil ; they are no longer bound together in loose aggregates, but are 

 separated so as to give the soil its most finely grained character. The deflocculation 

 is much diminished where superphosphate (an acid manure) is used in con juction with 

 the nitrate of soda.— The Gardenrs Chronicle. 



