666 PROCEEDINGS OF SECTION K. 



2. SOME PHYSICAL AND CHEMICAL FACTORS AFFECT- 

 ING SOIL FERTILITY AND THE GROWTH OF CROPS. 



By H. J. CoJhourn, Agricultural Expert and Chemist to the 

 Government of Tasmania. 



It is well known to the scientific agriculturist that the germina- 

 tion of the seed of any plant is dependent upon three principal 

 factors, viz., an adequate supply of oxygen, moisture, and warmth. 

 The growing plant continues to be dependent on these natural 

 agents, but when the reserve of food contained in the seed is done 

 with, it has to seek for food supplies in the soil which must offer as 

 little resistance as possible to the passage of its roots. Thorough 

 cultivation tends to bring about that texture of the soil which is 

 most favorable to plant growth. It is obvious, too, that a soil 

 once brought into good cultivation remains easier to work for a 

 good while to come ; hence the initial outlay may be spread over 

 a considerable period of time. Again, the presence of an abundant 

 supply of humus or decayed vegetable matter in the soil exerts a 

 very favorable effect upon its texture, and renders it less costly to 

 manipulate. This is a strong argument in favour of occasionally 

 ploughing in a green crop which, upon decay, furnishes much avail- 

 able plant food. Moreover, the production of carbonic acid, which 

 goes on during the process of decomposition, exerts a valuable in- 

 direct effect in liberating much mineral plant food from the re- 

 serve supplies of the soil. The green crop should be leguminous, if 

 jiossible, on account of the well-known property possessed by the 

 leguminous order of plants of gathering nitrogen from the atmo- 

 sphere, thus greatly enriching the soil with a valuable fertilizer. 

 A practical point worth noting in connexion with green manur- 

 ing is the liability of the soil after this treatment to be too hollow 

 for the crop that may be sown immediately afterwards. This con- 

 dition commonly occurs if dry weather sets in shortly after the 

 green crop is ploughed in, the result being the formation of air 

 cavities in the soil. This condition can be improved, or, perhaps, 

 remedied altogether by means of the roller, disc harrow, or other 

 suitable implement. The green crop during the early stages of its 

 decomposition in the soil sometimes develops an injurious degree of 

 sourness which, however, can be mitigated by applying a good 

 dressing of lime to the land at the time the ploughing in takes 

 place. 



Another important factor which concerns the amelioration of 

 the texture of soils is lime. This valuable substance acts both 

 chemically and physically upon the soil ; chemically, it promotes 

 nitrification, or the conversion of the crude nitrogen of the soil into 

 nitrate of lime — one of the best fertilizers ; it liberates potash 

 from its combinations, and renders it available for plant 

 food. To summarize matters — draining, liming, abundant 

 tillage, and the maintenance of a good supply of humus in the 

 soil are the chief factors in successful farming. Given these 

 a minimum amount of fertilizers is required, as so much of 



