378 THE SMALL GRAINS 



was on the ground (Guthrie and Helms, 1902, p. 5). 

 In northern Victoria, superphosphates were applied in 

 3-years trials on the demonstration farms, in connec- 

 tion both with continuous cropping of wheat and wheat 

 following summer fallow. The average results on the 

 3 farms for the third year, 1903, showed 6 bushels 

 to an acre more wheat on plats with superphosphates 

 than on plats not manured, under continuous cropping. 

 On summer fallow, the difference was about 6^ bushels in 

 favor of superphosphate fertilizers. The average rainfall 

 at one of these farms for three years was. about 12 inches, 

 but was 19 inches in 1903 (Howell, 1904, pp. 31-39). 



407. Humus is, without doubt, the greatest need in 

 soils of the Western area. The term humus is not cor- 

 rectly applied to all organic matter of the soil, as often 

 supposed, but only to a peculiar product of the partial 

 decay of such matter accomplished in a warm, moist 

 soil, in the presence of lime. Ordinarily fresh or coarse 

 organic matter only loosens the soil, sometimes injuriously, 

 and does not furnish nitrogen and mineral foods until 

 humified. 



Humus is of value to the soil in a number of ways: 

 (1) It improves the texture somewhat as lime does by 

 causing aggregation or flocculation of the clay particles 

 into a granular condition, and so favors aeration, warmth, 

 and easier cultivation; (2) prevents crusting of the soil 

 surface ; (3) absorbs water and water vapor ; (4) renders 

 mineral plant-foods available; (5) is the most reliable 

 source of nitrogen, which is kept in reserve and gradually 

 furnished to the roots of plants when most needed through 

 the action of bacteria; (6) contains small quantities of 

 mineral plant-foods that are considered to be immedi- 

 ately available. 



