February, 1910.] 



127 



SCIENTIFIC AGRICULTURE. 



CULTIVATION AND FERTILITY. 



(From the Agricultural News, Vol. 

 VIII., No, 184, May 15, 1909.) 

 Thorough and judicious cultivation is 

 essential for a soil to give its best results 

 as a crop-producing medium. Providing 

 a soil is well-drained, the more deeply 

 it is cultivated, the more extensive is 

 the area through which the plants can 

 forage in search of food, and thus it is 

 that improvement in tillage methods 

 which result in deepening the soil and 

 promoting nitrification, tend to have 

 the same effect as applications of 

 manure. 



The advantages of a deep soil, as com- 

 pared with a shallow soil, are obvious, 

 and — expressed concisely— these may be 

 said to consist in the fact that when 

 land is ploughed to a depth of no more 

 than 3 inches, the plants growing 

 thereon have 3 inches of food, while 

 when the land is ploughed 6 inches deep 

 the land has access to 6 inches of food, 

 and so on. The lower portions of the 

 soil are not so rich in available plant 

 food as the upper portions, but this 

 may be remedied to a large extent by 

 suitable cultivation, which results in 

 admitting air, moisture, and heat, the 

 necessary conditions under which ferti- 

 lity is developed. 



It need hardly be pointed out, how- 

 ever, that any deliberate attempt to 

 lower the line of division between the 

 soil and subsoil by deeper ploughing 

 should be carried out gradually and 

 with caution, and the most judicious 

 plan is to extend the operation over 

 several years, i.e., to plough just a 

 little deeper each season than was done 

 in the previous year. Many instances are 

 on record in which the fertility of land 

 remarkable for its crop-producing capa- 

 city has suffered enormously as the 

 result of lowering the depth of plough- 

 ing 2 or 3 inches below the normal level 

 in one season. This is because the sur- 

 face soil containing the organisms which 

 are responsible for the breaking down 

 of plant food has been buried, and 

 a heavy, raw, infertile subsoil brought 

 to the top. 



Another important point in connexion 

 with the capacity of the soil to return 

 large crops is its ability to retain mois- 

 ture. This power is greatest when the 

 land contains a good proprooion of 

 humus, is well tilled, thoroughly 

 pulverised, the subsoil firm, and the 



oil kept in the form of a loose mulch 



t the surface, 



As the result of all these conditions, 

 absorption of rain water takes place 

 readily, and this is retained instead of 

 rapidly drawing away. Water in a 

 cultivated soil is held in the form of thin 

 surface films enclosing each separate 

 particle. It is obvious, therefore, 

 that the more thoroughly the land is 

 pulverised by cultivation, the greater 

 will be the number of soil particles, and 

 the greater the capacity of the land to 

 retain moisture. The presence of 

 humus increases this storage capacity 

 and reduces evaporation. It has been 

 estimated by agricultural physicists 

 that a ton of humus will store over 

 seven times as much moisture as a 

 ton of sand, and further, that sand 

 loses its water by evaporation from 

 three to four times as rapidly as the 

 humus. Clay soils store only about one- 

 fourth as much moisture as humus, and 

 lose it by evaporation about twice as 

 rapidly. 



THE STERILISATION OF SOIL. 



(From the Gardeners' Chronicle, Vol. 

 XLVI, October 23, 1909.) 



Ever since it began to be realised that 

 the soil is the home of a great number of 

 minute organisms— bacteria and fungi — 

 as well as of larger organisms like 

 infusoria and eelworms, there have not 

 been wanting experiments in which at- 

 tempts were made to grow plants in soil 

 which had been deprived of these living 

 agencies. The results, however, that 

 have been reported have been contra- 

 dictory and difficult of explanation, and 

 when also of late years certain gardeners 

 began to use sterilised soil on a practical 

 scale there has been a similar conflict of 

 evidence as to the value of the treat- 

 ment. The gardener has tried soil 

 sterilisation, nearly always by heat, for 

 various reasons ; in the first place, he 

 hoped to get rid of the seeds of weeds 

 and the spores of the mosses and liver- 

 worts which encrust the surface of seed- 

 pans whenever germination is long 

 delayed ; again, he hoped to kill off the 

 spores of certain fungoid diseases which 

 harbour in the soil, and the eelworms 

 and similar organisms which often do so 

 much harm to cultures under glass. 

 Any process of sterilisation by heat, 

 involving the heating of the soil, either 

 wet or dry, to the temperature of boil- 

 ing water, must be expensive, but 

 whether it may prove to be commer- 

 cially profitable or not, it is only very 

 recently that we have learnt what sort 



