328 ANNUAL REPORT OF THE Off. Doc. 



the desired effe<'t until theiH' is a liberal applieaiion of lime. Limiug 

 should be recommended more for its value iu improAing the physi- 

 cal condition of verv heavy soils than for its action iu liberating 

 plant food. Whenever the soil is rendered flocculent by lime and 

 the addition of vegetable matter, then commercial fertilizers will be 

 niorc effective and the important woii; of the bacteria of the soil 

 Avill be greatly augmented. 



Again, the j)hysical properties of \ery sandy or gravelly soils are 

 not conducive to the growth of large crops, and the tiller should 

 consider how he might economically increase the supply of organic 

 matter instead of simj)ly the amount of the various elements of 

 plant food. 



HUMUS. 



The great problem before the American farmer is, how to main- 

 tain and increase the sujjply of humus in cultivated soils. Were 

 il simply a matter of preserving the supply of available food ele- 

 ments, the question would be greatly simplified. We would then 

 purchase in available forms the food elements needed. We would 

 not need to concern ourselves about manure, clover, cow peas and 

 green crops as means of increasing the fertility of the soil. 



The value of humus as a factor of soil fertility is not disputed, 

 t^oils rich in decaying vegetable matter are, as a rule, highly pro- 

 ductive, it was the enormous supply of humus in the western 

 prairie lands that induced farmers to seek those soils. It is the 

 large store of organic matter still found there that makes it possi- 

 ble to produce such large crops of cereals, and this accounts for the 

 very limited use of commercial fertilizers on western farms. 



It is diilicult to comprehend the full value of humus in the feeding 

 of jdants. All the factors of soil fertility are more or less influenced 

 by the supply of decaying vegetable matter. Soils rich in humus 

 are dark in color, and this means a warm soil, as dark colors ab- 

 sorb more heat than light ones. Chemical changes and bacterial 

 life are more active in warm soils, hence, plants iu such soils grow 

 rapidly on accoimt of the available supj)ly of plant food. This fact 

 is especially recognized by market gardeners whose profits are 

 largely determined by the early maturity of their crops. Humus, 

 when added in sufficient quantity, impi'oves the tilth of the soil, 

 making it lighter and more friable, thus decreasing the labor ner- 

 essary for tillage. Humus renders the particles of stiff soils less 

 resistant to root growth. Humus absorbs and holds water to a 

 gi-eater extent than any other soil ingredient, iliimns l)inds to- 

 gether the loose particles of sandy and gravelly soils, rendering 

 tluni more retentive of moisture and i)lant food. Humus aids in 

 the decom])osition of the miiienil mutters of the soil by whi<-ii un- 



