

TYPES OF SOIL 37 



becomes whitened with incrustations of alkali in many places to 

 such an extent that it looks like a white mantle of snow. A large 

 part of the lands in the arid regions of the United States are 

 alkaline in their nature, and white alkaline incrustations may often 

 be seen along the banks of streams and of many of the irrigating 

 ditches found in this region. Such soils are often very fertile, as 

 they have not been leached out by heavy rains; consequently 

 they yield large returns when properly cultivated and sufficiently 

 irrigated. The Salt River Valley and the Gila Valley of Arizona, 

 the Pecos Valley of New Mexico, together with portions of Cali- 

 fornia, Colorado, and Nevada, are striking examples of this fact. 



Semiarid Lands. In northwestern Texas, and also in the 

 western portions of Oklahoma, Kansas, and Nebraska we find lands 

 that are only half watered and are designated as semiarid lands. 

 These soils are of a loose sandy nature and contain sufficient mois- 

 ture to insure a good growth of wild prairie grass and buffalo grass 

 during the greater portion of the year. The rainfall here varies 

 from five to twenty-five inches. 



Humid Soils. These are soils that have plenty of rain and 

 moisture. Vegetation of such soils is of rapid growth on account 

 of the moisture present, but they really contain much less plant 

 food than arid lands because the heavy rains wash away the nutri- 

 tive elements of the soil. Characteristic soils of this kind are found 

 in the Mississippi River Valley region and in many other parts of 

 the United States. In some portions of the State of Washington 

 the rainfall frequently is over one hundred inches per year. 



EXERCISES 



1. Secure a pint of sand, a pint of clay, and a pint of ordinary soil. 

 Weigh each and record your results. 



2. Heat each sample for some time and weigh again. Explain the re- 

 sults. 



3. Place each sample in a vessel and add much water. Drain off the 

 water not absorbed and weigh again. Note results and explain. 



4. Expose each sample to the action of the sun and wind. Note results 

 and explain. 



5. Plant some seed in each sample of soil and watch the growth rate and 

 development. 



6. Test the temperature of the samples of soil used above and compare the 

 temperatures. 



