246 EXPERIMENTAL FARMS 



4 GEORGE V., A. 19U 



of 95 per cent carbonate of lime, and some of these have been utilized in the manufac- 

 ture of cement. 



Of all the naturally-occurring sources of lime, marl is one of the most valuable 

 and the cheapest for agricultural purposes. It is not to be regarded as a fertilizer 

 (that term being now restricted to materials furnishing one or more of the following 

 essential elements — nitrogen, phosphoric acid and potash — in notable amounts), but 

 it is an amendment of very considerable importance. It may be used for the improve- 

 ment of many types of soil — clays, sandy loams and peaty soils. This it accomplishes, 

 first, by favourably altering their physical condition or texture. Especially is r 

 the case with heavy clay loams upon which lime (or carbonate of lime) has the effect 

 of destroying plasticity and rendering them more permeable to air and the passage 

 of water. Thus it is that liming or marling such soils makes them mellower, more 

 easily worked and affords the root system better facilities for rapid extension. 



Secondly, it furnishes lime in a form agreeable to crop growth. Lime is a normal 

 constituent of plant tissues, and crops need it for their development. It is for this 

 reason that no soil can be accounted at its best that does not contain an appreciable 

 amount of this element in an available form. Continued cropping reduces the store 

 of available lime (and many soils are, originally, but poorly supplied) and further, 

 in the course of time, washes down below the range of the feeding roots. We have in 

 these facts the explanation why an occasional liming or marling is frequently bene- 

 ficial, even on soils originally well furnished with this element. 



Again, through the loss of lime, or rather carbonate of lime, and imperfect 

 drainage, soils are apt to become sour, and it is generally recognized that soils only 

 slightly acid are not congenial to the majority of farm crops. Lime or marl or ground 

 limestone corrects this acidity and restores conditions favourable to plant growth. 

 Acidity of soil is one of the causes of failure of the clover crop, and thus it has fre- 

 quently been found that an application of lime, either as such or as marl or ground 

 limestone, has been sufficient to ensure a good growth of this valuable crop, where 

 before such could not be obtained. 



And, thirdly, the micro-organisms engaged in the nitrification of the organic 

 matter, which means the preparation or conversion of the inert nitrogen of the soil 

 into forms suitable for the use of crops, cannot perform their important function in 

 an acid soil, one which is deficient in available lime. This is also true of nitrogen- 

 fixing bacteria, those which have the ability to fix atmospheric nitrogen without the 

 aid of leguminous crops, as well as those associated with the legumes in this all- 

 ; mportant work. One of the vital factors towards the development and activity of 

 these organisms is a neutral or slightly alkaline soil, and it is in this we have the 

 explanation that an application of lime in some alkaline form may vastly mere 

 the productiveness of a soil, without having materially added to its store of plant 

 food. 



To sum up this discussion of the function of lime, as such or in the form of car- 

 nate, for it must be remembered that it is in the form of the bitter compound that 

 >laked or quick lime exists soon after its admixture with the soil, the presence of 

 carbonate of lime, then, whether supplied as lime, marl or finely-ground limestone. 

 Performs a very important triple role — physically, chemically and biologically — in 

 influencing for good a soil's productiveness. 



Physically, it is of value to all classes of soils, lightening and mellowing heavy 

 clays and cementing and giving 'body' to sandy loams. For the improvement of 

 texture it plays a most important part, especially in conjunction with efficient drain- 

 age, right culture and the supplying of organic matter. 



From the chemical standpoint, it is first to be regarded as plant fond, and hence 

 indispensible to the best results for all soils deficient in lime. This deficiency may 

 be due to the character of the rocks that formed the mineral basis of the soil or it may 

 have arisen through a long term of cropping and the leaching out of soluble lime 



