OREGON FARMER 47 



the possession of a soil cover of unusual natural fertility and great 

 endurance under cropping. Great natural fertility or "strength" 

 of soil is the most valuable agricultural asset a country may possess. 

 The soils of the state may be roughly divided into four great 

 classes, which in order of importance are as follows: 



The Silt Loams. This is the most widespread and most important 

 soil class. The silt loams are found in large areas in practically 

 every county in the state. For total production; for adaption to 

 the widest variety of crops; for natural fertility and for most other 

 desirable farming qualities; this class of soils is the most valuable 

 in Oregon. While the silt loams vary in composition in different 

 parts of the state, their important qualities remain fairly constant. 

 They are universally of high plant food content, particularly in 

 total potassium and phosphorus^ yet their greatest claim to product- 

 iveness is their physical character. The average Oregon silt loams 

 are a happy medium between the sandy loam on the one hand and 

 the clay loam on the other, having the bad qualities of neither and 

 the good qualities of both. Often called "volcanic ash" soils, 

 particularly in Eastern Oregon, because of their origin and uniformly 

 fine, powdery texture they are derived largely from the volcanic 

 basalt, a fine grained dark gray rock high in the mineral plant food 

 elements. The weathered products of this rock, alluvially deposited 

 and mixed with organic matter hi greater or less degree, according 

 to the precipitation of the region, form the soil cover of the great 

 valley floors of Western Oregon, the rolling plateau lands of the 

 Columbia Basin, and the inter-mountain valleys of Eastern Oregon. 



As their name implies, the chief component of the soils of this 

 class is silt, which is intermediate in texture or size of particles 

 between the clay component on the one hand and the finest grade 

 of sand on the other. Analyses of many samples of Oregon silt 

 loams show their general composition to be, roughly, as shown in 

 table, page 46. 



As shown, they are a very uniformly fine grained powdery soil 

 having the desirable qualities of clay for the retention of moisture 

 and plant foods and large surface area for the breaking down of 

 plant foods through chemical and bacterial activities and for feeding 

 plant roots, but because of the relatively small amount of the clay 

 component contained as compared with the amount of silt, these 

 soils drain quickly, warm up and become mellow earlier and handle 

 more easily through a longer working and growing season than the 

 clay loam type. The cold slowness, puddling, clodding, baking, 

 and cracking qualities common to clay soils are absent. On the 

 other hand, they contain little sand and do not dry out during drouth 

 or leach of plant foods as do the sandy loams. Physically this class 

 of soil requires for its maintenance in the highest state of fertility 

 additions of (1) humus forming material through good rotations 

 and (2)fampleJ cultivation. To both extra humus additions and 

 extra tillage, silt loams respond quick and generously. The 



