160 PRACTICAL FARM CHEMISTRY. 



substances named in small quantities at a reason- 

 ably cheap figure. Even without actual trial of 

 chemical fertilizers, however, we can get an estimate 

 of the needs of the soil by the appearance of the 

 plants. If all our crops, under fair, atmospheric 

 conditions, come up with a rich, dark green color, 

 and grow luxuriantly, we may be sure that the soil 

 is well provided with nitrogen. If they are yellow 

 and sickly from the start, this element, most likely, 

 is in scant supply. Nitrate of soda, in such case, 

 will usually make a great improvement, and this 

 very promptly. Clover is less dependent on a sur- 

 plus of available nitrogen, and should it refuse to 

 grow thriftily, we may make up our mind that the 

 soil is deficient in potash. The same conclusion 

 would be justified, should potatoes grow plenty of 

 top and little tuber. Still with this crop full success 

 depends on so many other conditions, that we might 

 well call it fickle, and hesitate to base too much 

 confidence upon its behavior. The failure of wheat 

 and corn to produce grain on well developed straw^ 

 or stalks would lead us to suspect scarcity of phos- 

 phoric acid as the chief cause. Observation and 

 good judgment in all these things have to come to 

 our aid in making a correct soil diagnosis. 



