138 EXPERIMENTAL FARMS. 



CLOVERS AS GREEN MANURKS. 



■ THE FACTORS OP SOIL FERTILITY. 



A high degree of soil fertility or crop-producing power is one of the fundamental 

 factors in profitable farming. It, therefore, becomes of the greatest, indeed of paramount, 

 importance to understand the nature of what constitutes fertility in a soil. 



First, the soil must contain at least certain minimum amounts of mineral matter, 

 such as potash, phosphoric acid and lime, and these constituents, or rather a certain 

 percentage of them, must be in a more or less readily assimilable condition ; for in this 

 connection it is well to point out that by far the larger proportion of the fertilizing 

 elements present in a soil is in locked-up or insoluble combinations. Plant food from 

 the soil is absorbed and appropriated by crops in the form of a solution, and conse- 

 quently such compounds as are insoluble, or are not capable of solution by the soil water 

 or the exudations of plant rootlets, are valueless from an agricultural standpoint. 



Secondly, a soil to be fertile must be possessed of nitrogen and humus. The latter 

 term is applied to semi-decomposed organic matter, arising from the partial decay of 

 roots and vegetable tissues generally. The nitrogen is in combination with this organic 

 matter and is converted into forms useful to plants (nitrates) by a process known as 

 nitrification. This conversion is the work of certain microbes, or microscopic plants 

 which live on humus. Their development is in a large measure regulated by the 

 amount of humus present, the degree of soil moisture, the soil's temperature, and the 

 percentage of salifiable bases, such as lime and potash, present to combine with the 

 nitric acid as formed. Permeability of the soil to air is also necessary. 



Thirdly, fertility depends upon a right mechanical condition of the soil. This is 

 sometimes known as tilth. It should be such that air may readily permeate and rain 

 easily penetrate the soil. Roots and rootlets should be able to find an easy passage in 

 foraging for food. Drainage and good cultural methods are essential in bringing about 

 good tilth. 



Fourth, certain conditions of climate are necessary for the best results. Warmth, 

 sunshine and rainfall are all potent influences on crop production. 



GREEN MANURING FOR INCREASING SOIL FERTILITY. 



The system of green manuring, as practised by turning under a green crop of clover, 

 increases fertility in a greater or less degree by the means named in the first three 

 counts. While it does not add to the total amount of mineral plant food in the soil, the 

 growth of the clover converts a large portion of such into compounds which, upon decay 

 or rotting of the crop, are more readily assimilable for future use. This is certainly of 

 no small value. 



The feature of special importance, however, is that the decay of the clover enriches 

 the soil in nitrogen and organic matter — a distinct gain, since all the elements of the 

 latter, and the greater portion of the former, have been appropriated by the clover plant 

 from the atmosphere. This organic nitrogen, as it may be termed, is readily transformed, 

 in the presence of lime or potash and under favourable conditions of climate, into 

 nitrates, the compounds which ordinary farm crops draw upon for their supply of 

 nitrogen. As much nitrogen can be furnished per acre by ploughing down a crop of 

 clover as would be furnished by an application of 10 to 15 tons of barn-yard manure. 

 Again, the addition of the large amount of humus by a crop of clover vastly improves 

 the texture of the soil, opening up and making warmer a clay loam and rendering a 

 sandy soil more absorptive. 



There are other benefits accruing from this system of manuring, but, in addition to 

 those just discussed, attention need now only be directed to the following : — During 

 the hot months of summer the process of nitrification goes on rapidly. The nitrates so 



