20 FUNDAMENTALS OF AGRICULTURE. 



ration at the surface of the ground are therefore ques- 

 tions of the utmost importance.. The amount of cap- 

 illary water which the soil can hold is influenced by 

 the mechanical composition of the soil, its condition of 

 granulation, and the height of the surface above the 

 ground water table, or saturated portion of the subsoil. 

 Coarse sands are able to hold only a small amount of 

 capillary water so that coarse sandy soils often shortly 

 after rains will be found to have gained only from five 

 to ten per cent, by weight of water. Finer soils, such 

 as sandy loams and silt loams will retain from fifteen 

 to twenty-five per cent., while heavier clay soils retain 

 from thirty to forty or even fifty per cent, of water, 

 expressed in per cent, of the weight of water to that 

 of dry soil. Since, as previously stated, humus has a 

 large water-holding capacity, soils in which this sub- 

 stance is abundant retain much more water than those 

 in which it is small in amount. A large part of the 

 advantage which clay loam soils have over the sandy 

 soils is on account of their larger water-holding ca- 

 pacity. This is especially true with reference to the 

 growing of crops, such as grasses for pasture or hay 

 purposes. The grass growing throughout the season 

 requires a soil with a large water-holding capacity to 

 enable it to continue growing during the absence of 

 rain for a period of a few weeks. The grasses have 

 developed an extremely fine root system which enables 

 them to penetrate clay soils and so take advantage of 

 their large water-holding capacity. Such heavy clay 

 soils are, therefore, often spoken of as grass soils. 



Produce Soil Mulch by Frequent Shallow Cultiva- 

 tion. Since a great deal of the capillary water is lost 

 by soils on account of its being drawn up to the surface 

 and evaporated, it is important if possible to prevent 

 this evaporation. This may be done by producing a 

 soil mulch. It is a simple experiment to get a small 

 stream of water falling on a board to follow the path 

 made for it by drawing a wet finger over it and mak- 

 ing a moistened surface in a zigzag path. The water 



