WHAT SOILS ARE BEST FOR AGRICULTURE? 



in the soil from passing out by evaporation. In some 

 places farmers can only grow one crop every other year 

 because of the small amount of water. In such cases, 

 the farmer keeps half of his land under cultivation, and 

 the other half covered with straw or a surface mulch so 

 as to allow it to accumulate water. Thus a crop is raised 

 every two years without the addition of more moisture 

 than the soil holds by reason of its mulch. 



Demonstration 4. To Show That Certain Mineral Substances Are 

 Needed for Plant Life. 



For this experiment use five wide-mouth bottles : one con- 

 taining a nutrient solution with all the necessary minerals, and 

 each of the other four containing a nutrient solution l lacking 



start tkef experiment) vih younfe 

 all about I the same 







either iron, calcium, potassium, or nitrogen. In these bottles 

 place young seedlings, and allow them to grow for several weeks. 

 Note the results. What mineral substances are necessary for 

 the growth of green plants? 



1 The control nutrient solution is made up as follows : 



Distilled water 1000 to 1500 grams 



Potassium nitrate 1.0 gram 



Magnesium sulphate 0.5 gram 



Calcium sulphate 0.5 gram 



Calcium or potassium phosphate . . . 0.5 gram 

 To this solution a trace of some iron salt, as ferric phosphate, should be 

 added. 



If you do not have the facilities for making the solutions needed, have 

 a druggist weigh out the required amounts of the several different substances 

 and add to distilled water, as suggested in the experiment. 

 H. & w. sci. i 17 



